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L_0294 | saturn | T_1647 | Most of Saturns moons are very small, and only seven are large enough for gravity to have made them spherical. Only Titan is larger than Earths Moon at about 1.5 times its size. Titan is even larger than the planet Mercury. Scientists are interested in Titan because its atmosphere is similar to what Earths was like before life developed. Nitrogen is dominant and methane is the second most abundant gas. Titan may have a layer of liquid water and ammonia under a layer of surface ice. Lakes of liquid methane (CH4 ) and ethane (C2 H6 ) are found on Titans surface. Although conditions are similar enough to those of early Earth for scientists to speculate that extremely A color-exaggerated mosaic of Saturn and its rings taken by Cassini as Saturn eclipses the Sun. A close-up of Saturns outer C ring show- ing areas with higher particle concentra- tion and gaps. This composite image compares Saturns largest moon, Titan (right) to Earth (left). Click image to the left or use the URL below. URL: | text | null |
L_0294 | saturn | T_1647 | Most of Saturns moons are very small, and only seven are large enough for gravity to have made them spherical. Only Titan is larger than Earths Moon at about 1.5 times its size. Titan is even larger than the planet Mercury. Scientists are interested in Titan because its atmosphere is similar to what Earths was like before life developed. Nitrogen is dominant and methane is the second most abundant gas. Titan may have a layer of liquid water and ammonia under a layer of surface ice. Lakes of liquid methane (CH4 ) and ethane (C2 H6 ) are found on Titans surface. Although conditions are similar enough to those of early Earth for scientists to speculate that extremely A color-exaggerated mosaic of Saturn and its rings taken by Cassini as Saturn eclipses the Sun. A close-up of Saturns outer C ring show- ing areas with higher particle concentra- tion and gaps. This composite image compares Saturns largest moon, Titan (right) to Earth (left). Click image to the left or use the URL below. URL: | text | null |
L_0299 | scientific models | T_1662 | Scientific models are useful tools in science. Earths climate is extremely complex, with many factors that are dependent on one another. Such a system is impossible for scientists to work with as a whole. To deal with such complexity, scientists may create models to represent the system that they are interested in studying. Scientists must validate their ideas by testing. A model can be manipulated and adjusted far more easily than a real system. Models help scientists understand, analyze, and make predictions about systems that would be impossible to study as a whole. If a scientist wants to understand how rising CO2 levels will affect climate, it will be easier to model a smaller portion of that system. For example, he may model how higher levels of CO2 affect plant growth and the effect that will have on climate. | text | null |
L_0299 | scientific models | T_1663 | How can scientists know if a model designed to predict the future is likely to be accurate, since it may not be possible to wait long enough to see if the prediction comes true? One way is to run the model using a time in the past as the starting point see if the model can accurately predict the present. A model that can successfully predict the present is more likely to be accurate when predicting the future. Many models are created on computers because only computers can handle and manipulate such enormous amounts of data. For example, climate models are very useful for trying to determine what types of changes we can expect as the composition of the atmosphere changes. A reasonably accurate climate model would be impossible on anything other than the most powerful computers. | text | null |
L_0299 | scientific models | T_1664 | Since models are simpler than real objects or systems, they have limitations. A model deals with only a portion of a system. It may not predict the behavior of the real system very accurately. But the more computing power that goes into the model and the care with which the scientists construct the model can increase the chances that a model will be accurate. | text | null |
L_0299 | scientific models | T_1665 | Physical models are smaller and simpler representations of the thing being studied. A globe or a map is a physical model of a portion or all of Earth. Conceptual models tie together many ideas to explain a phenomenon or event. Mathematical models are sets of equations that take into account many factors to represent a phenomenon. Mathematical models are usually done on computers. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0300 | seafloor spreading hypothesis | T_1666 | Harry Hess was a geology professor and a naval officer who commanded an attack transport ship during WWII. Like other ships, Hesss ship had echo sounders that mapped the seafloor. Hess discovered hundreds of flat-topped mountains in the Pacific that he gave the name guyot. He puzzled at what could have formed mountains that appeared to be eroded at the top but were more than a mile beneath the sea surface. Hess also noticed trenches that were as much as 7 miles deep. Meanwhile, other scientists like Bruce Heezen discovered the underwater mountain range they called the Great Global Rift. Although the rift was mostly in the deep sea, it occasionally came close to land. These scientists thought the rift was a set of breaks in Earths crust. The final piece that was needed was the work of Vine and Matthews, who had discovered the bands of alternating magnetic polarity in the seafloor symmetrically about the rift. | text | null |
L_0300 | seafloor spreading hypothesis | T_1667 | The features of the seafloor and the patterns of magnetic polarity symmetrically about the mid-ocean ridges were the pieces that Hess needed. He resurrected Wegeners continental drift hypothesis and also the mantle convection idea of Holmes. Hess wrote that hot magma rose up into the rift valley at the mid-ocean ridges. The lava oozed up and forced the existing seafloor away from the rift in opposite directions. Since magnetite crystals point in the direction of the magnetic north pole as the lava cools, the different stripes of magnetic polarity revealed the different ages of the seafloor. The seafloor at the ridge is from the Brunhes normal; beyond that is basalt from the Matuyama reverse; and beyond that from the Gauss normal. Hess called this idea seafloor spreading. As oceanic crust forms and spreads, moving away from the ridge crest, it pushes the continent away from the ridge axis. If the oceanic crust reaches a deep sea trench, it sinks into the trench and is lost into the mantle. The oldest crust is coldest and lies deepest in the ocean because it is less buoyant than the hot new crust. Hess could also use seafloor spreading to explain the flat topped guyots. He suggested that they were once active volcanoes that were exposed to erosion above sea level. As the seafloor they sat on moved away from the ridge, the crust on which they sat become less buoyant and the guyots moved deeper beneath sea level. | text | null |
L_0300 | seafloor spreading hypothesis | T_1668 | Seafloor spreading is the mechanism for Wegeners drifting continents. Convection currents within the mantle take the continents on a conveyor-belt ride of oceanic crust that, over millions of years, takes them around the planets surface. The spreading plate takes along any continent that rides on it. Click image to the left or use the URL below. URL: | text | null |
L_0301 | seasons | T_1669 | A common misconception is that the Sun is closer to Earth in the summer and farther away from it during the winter. Instead, the seasons are caused by the 23.5o tilt of Earths axis of rotation relative to its plane of orbit around the Sun (Figure 1.1). Solstice refers to the position of the Sun when it is closest to one of the poles. At summer solstice, June 21 or 22, Earths axis points toward the Sun and so the Sun is directly overhead at its furthest north point of the year, the Tropic of Cancer (23.5o N). During the summer, areas north of the Equator experience longer days and shorter nights. In the Southern Hemi- sphere, the Sun is as far away as it will be and so it is their winter. Locations will have longer nights and shorter days. The opposite occurs on winter solstice, which begins on December 21. More about seasons can be found in the Atmospheric Processes chapter. | text | null |
L_0301 | seasons | T_1670 | Different parts of the Earth receive different amounts of solar radiation. Which part of the planet receives the most solar radiation? The Suns rays strike the surface most directly at the Equator. Different areas also receive different amounts of sunlight in different seasons. What causes the seasons? The seasons are caused by the direction Earths axis is pointing relative to the Sun. The Earth revolves around the Sun once each year and spins on its axis of rotation once each day. This axis of rotation is tilted 23.5o relative to its plane of orbit around the Sun. The axis of rotation is pointed toward Polaris, the North Star. As the Earth orbits the Sun, the tilt of Earths axis stays lined up with the North Star. | text | null |
L_0301 | seasons | T_1671 | The North Pole is tilted towards the Sun and the Suns rays strike the Northern Hemisphere more directly in summer (Figure 1.2). At the summer solstice, June 21 or 22, the Suns rays hit the Earth most directly along the Tropic of Cancer (23.5o N); that is, the angle of incidence of the Suns rays there is zero (the angle of incidence is the deviation in the angle of an incoming ray from straight on). When it is summer solstice in the Northern Hemisphere, it is winter solstice in the Southern Hemisphere. | text | null |
L_0301 | seasons | T_1672 | Winter solstice for the Northern Hemisphere happens on December 21 or 22. The tilt of Earths axis points away from the Sun (Figure 1.3). Light from the Sun is spread out over a larger area, so that area isnt heated as much. With fewer daylight hours in winter, there is also less time for the Sun to warm the area. When it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere. | text | null |
L_0301 | seasons | T_1673 | Halfway between the two solstices, the Suns rays shine most directly at the Equator, called an equinox (Figure 1.4). The daylight and nighttime hours are exactly equal on an equinox. The autumnal equinox happens on September 22 or 23 and the vernal, or spring, equinox happens March 21 or 22 in the Northern Hemisphere. Summer solstice in the Northern Hemisphere. Click image to the left or use the URL below. URL: | text | null |
L_0302 | seawater chemistry | T_1674 | Remember that H2 O is a polar molecule, so it can dissolve many substances (Figure 1.1). Salts, sugars, acids, bases, and organic molecules can all dissolve in water. | text | null |
L_0302 | seawater chemistry | T_1675 | Where does the salt in seawater come from? As water moves through rock and soil on land it picks up ions. This is the flip side of weathering. Salts comprise about 3.5% of the mass of ocean water, but the salt content, or salinity, is different in different locations. What would the salinity be like in an estuary? Where seawater mixes with fresh water, salinity is lower than average. What would the salinity be like where there is lots of evaporation? Where there is lots of evaporation but little circulation of water, salinity can be much higher. The Dead Sea has 30% salinity nearly nine times the average salinity of ocean water (Figure 1.2). Why do you think this water body is called the Dead Sea? In some areas, dense saltwater and less dense freshwater mix, and they form an immiscible layer, just like oil and water. One such place is a "cenote", or underground cave, very common in certain parts of Central America. Ocean water is composed of many sub- stances, many of them salts such as sodium, magnesium, and calcium chlo- ride. Because of the increased salinity, the wa- ter in the Dead Sea is very dense, it has such high salinity that people can easily float in it! | text | null |
L_0302 | seawater chemistry | T_1675 | Where does the salt in seawater come from? As water moves through rock and soil on land it picks up ions. This is the flip side of weathering. Salts comprise about 3.5% of the mass of ocean water, but the salt content, or salinity, is different in different locations. What would the salinity be like in an estuary? Where seawater mixes with fresh water, salinity is lower than average. What would the salinity be like where there is lots of evaporation? Where there is lots of evaporation but little circulation of water, salinity can be much higher. The Dead Sea has 30% salinity nearly nine times the average salinity of ocean water (Figure 1.2). Why do you think this water body is called the Dead Sea? In some areas, dense saltwater and less dense freshwater mix, and they form an immiscible layer, just like oil and water. One such place is a "cenote", or underground cave, very common in certain parts of Central America. Ocean water is composed of many sub- stances, many of them salts such as sodium, magnesium, and calcium chlo- ride. Because of the increased salinity, the wa- ter in the Dead Sea is very dense, it has such high salinity that people can easily float in it! | text | null |
L_0302 | seawater chemistry | T_1676 | With so many dissolved substances mixed in seawater, what is the density (mass per volume) of seawater relative to fresh water? Water density increases as: salinity increases temperature decreases pressure increases Differences in water density are responsible for deep ocean currents, as will be discussed in the "Deep Ocean Currents" concept. Click image to the left or use the URL below. URL: | text | null |
L_0303 | sedimentary rock classification | T_1677 | Rock Conglomerate Breccia Sandstone Siltstone Shale Sediment Size Large Large Sand-sized Silt-sized, smaller than sand Clay-sized, smallest Other Features Rounded Angular When sediments settle out of calmer water, they form horizontal layers. One layer is deposited first, and another layer is deposited on top of it. So each layer is younger than the layer beneath it. When the sediments harden, the layers are preserved. Sedimentary rocks formed by the crystallization of chemical precipitates are called chemical sedimentary rocks. As discussed in the concepts on minerals, dissolved ions in fluids precipitate out of the fluid and settle out, just like the halite in Figure 1.1. The evaporite, halite, on a cobble from the Dead Sea, Israel. Biochemical sedimentary rocks form in the ocean or a salt lake. Living creatures remove ions, such as calcium, magnesium, and potassium, from the water to make shells or soft tissue. When the organism dies, it sinks to the ocean floor to become a biochemical sediment, which may then become compacted and cemented into solid rock (Figure 1.2). Table 1.2 shows some common types of sedimentary rocks. Breccia Clastic Sandstone Clastic Siltstone Clastic Shale Clastic Rock Salt Chemical precipitate Dolostone Chemical precipitate Limestone Bioclastic (sediments from organic materials, or plant or animal re- mains) Coal Organic Click image to the left or use the URL below. URL: | text | null |
L_0303 | sedimentary rock classification | T_1677 | Rock Conglomerate Breccia Sandstone Siltstone Shale Sediment Size Large Large Sand-sized Silt-sized, smaller than sand Clay-sized, smallest Other Features Rounded Angular When sediments settle out of calmer water, they form horizontal layers. One layer is deposited first, and another layer is deposited on top of it. So each layer is younger than the layer beneath it. When the sediments harden, the layers are preserved. Sedimentary rocks formed by the crystallization of chemical precipitates are called chemical sedimentary rocks. As discussed in the concepts on minerals, dissolved ions in fluids precipitate out of the fluid and settle out, just like the halite in Figure 1.1. The evaporite, halite, on a cobble from the Dead Sea, Israel. Biochemical sedimentary rocks form in the ocean or a salt lake. Living creatures remove ions, such as calcium, magnesium, and potassium, from the water to make shells or soft tissue. When the organism dies, it sinks to the ocean floor to become a biochemical sediment, which may then become compacted and cemented into solid rock (Figure 1.2). Table 1.2 shows some common types of sedimentary rocks. Breccia Clastic Sandstone Clastic Siltstone Clastic Shale Clastic Rock Salt Chemical precipitate Dolostone Chemical precipitate Limestone Bioclastic (sediments from organic materials, or plant or animal re- mains) Coal Organic Click image to the left or use the URL below. URL: | text | null |
L_0304 | sedimentary rocks | T_1678 | Sandstone is one of the common types of sedimentary rocks that form from sediments. There are many other types. Sediments may include: fragments of other rocks that often have been worn down into small pieces, such as sand, silt, or clay. organic materials, or the remains of once-living organisms. chemical precipitates, which are materials that get left behind after the water evaporates from a solution. Rocks at the surface undergo mechanical and chemical weathering. These physical and chemical processes break rock into smaller pieces. Mechanical weathering simply breaks the rocks apart. Chemical weathering dissolves the less stable minerals. These original elements of the minerals end up in solution and new minerals may form. Sediments are removed and transported by water, wind, ice, or gravity in a process called erosion (Figure 1.1). Much more information about weathering and erosion can be found in the chapter Surface Processes and Landforms. Streams carry huge amounts of sediment (Figure 1.2). The more energy the water has, the larger the particle it can carry. A rushing river on a steep slope might be able to carry boulders. As this stream slows down, it no longer has the energy to carry large sediments and will drop them. A slower moving stream will only carry smaller particles. Water erodes the land surface in Alaskas Valley of Ten Thousand Smokes. Sediments are deposited on beaches and deserts, at the bottom of oceans, and in lakes, ponds, rivers, marshes, and swamps. Landslides drop large piles of sediment. Glaciers leave large piles of sediments, too. Wind can only transport sand and smaller particles. The type of sediment that is deposited will determine the type of sedimentary rock that can form. Different colors of sedimentary rock are determined by the environment where they are deposited. Red rocks form where oxygen is present. Darker sediments form when the environment is oxygen poor. Click image to the left or use the URL below. URL: | text | null |
L_0304 | sedimentary rocks | T_1678 | Sandstone is one of the common types of sedimentary rocks that form from sediments. There are many other types. Sediments may include: fragments of other rocks that often have been worn down into small pieces, such as sand, silt, or clay. organic materials, or the remains of once-living organisms. chemical precipitates, which are materials that get left behind after the water evaporates from a solution. Rocks at the surface undergo mechanical and chemical weathering. These physical and chemical processes break rock into smaller pieces. Mechanical weathering simply breaks the rocks apart. Chemical weathering dissolves the less stable minerals. These original elements of the minerals end up in solution and new minerals may form. Sediments are removed and transported by water, wind, ice, or gravity in a process called erosion (Figure 1.1). Much more information about weathering and erosion can be found in the chapter Surface Processes and Landforms. Streams carry huge amounts of sediment (Figure 1.2). The more energy the water has, the larger the particle it can carry. A rushing river on a steep slope might be able to carry boulders. As this stream slows down, it no longer has the energy to carry large sediments and will drop them. A slower moving stream will only carry smaller particles. Water erodes the land surface in Alaskas Valley of Ten Thousand Smokes. Sediments are deposited on beaches and deserts, at the bottom of oceans, and in lakes, ponds, rivers, marshes, and swamps. Landslides drop large piles of sediment. Glaciers leave large piles of sediments, too. Wind can only transport sand and smaller particles. The type of sediment that is deposited will determine the type of sedimentary rock that can form. Different colors of sedimentary rock are determined by the environment where they are deposited. Red rocks form where oxygen is present. Darker sediments form when the environment is oxygen poor. Click image to the left or use the URL below. URL: | text | null |
L_0305 | seismic waves | T_1679 | Energy is transmitted in waves. Every wave has a high point called a crest and a low point called a trough. The height of a wave from the center line to its crest is its amplitude. The distance between waves from crest to crest (or trough to trough) is its wavelength. The parts of a wave are illustrated in Figure 1.1. | text | null |
L_0305 | seismic waves | T_1680 | The energy from earthquakes travels in waves. The study of seismic waves is known as seismology. Seismologists use seismic waves to learn about earthquakes and also to learn about the Earths interior. One ingenious way scientists learn about Earths interior is by looking at earthquake waves. Seismic waves travel outward in all directions from where the ground breaks and are picked up by seismographs around the world. Two types of seismic waves are most useful for learning about Earths interior. | text | null |
L_0305 | seismic waves | T_1681 | P-waves and S-waves are known as body waves because they move through the solid body of the Earth. P-waves travel through solids, liquids, and gases. S-waves only move through solids (Figure 1.2). Surface waves only travel along Earths surface. In an earthquake, body waves produce sharp jolts. They do not do as much damage as surface waves. P-waves (primary waves) are fastest, traveling at about 6 to 7 kilometers (about 4 miles) per second, so they arrive first at the seismometer. P-waves move in a compression/expansion type motion, squeezing and S-waves (secondary waves) are about half as fast as P-waves, traveling at about 3.5 km (2 miles) per second, and arrive second at seismographs. S-waves move in an up and down motion perpendicular to the direction of wave travel. This produces a change in shape for the Earth materials they move through. Only solids resist a change in shape, so S-waves are only able to propagate through solids. S-waves cannot travel through liquid. | text | null |
L_0305 | seismic waves | T_1681 | P-waves and S-waves are known as body waves because they move through the solid body of the Earth. P-waves travel through solids, liquids, and gases. S-waves only move through solids (Figure 1.2). Surface waves only travel along Earths surface. In an earthquake, body waves produce sharp jolts. They do not do as much damage as surface waves. P-waves (primary waves) are fastest, traveling at about 6 to 7 kilometers (about 4 miles) per second, so they arrive first at the seismometer. P-waves move in a compression/expansion type motion, squeezing and S-waves (secondary waves) are about half as fast as P-waves, traveling at about 3.5 km (2 miles) per second, and arrive second at seismographs. S-waves move in an up and down motion perpendicular to the direction of wave travel. This produces a change in shape for the Earth materials they move through. Only solids resist a change in shape, so S-waves are only able to propagate through solids. S-waves cannot travel through liquid. | text | null |
L_0305 | seismic waves | T_1682 | By tracking seismic waves, scientists have learned what makes up the planets interior (Figure 1.4). P-waves slow down at the mantle core boundary, so we know the outer core is less rigid than the mantle. S-waves disappear at the mantle core boundary, so we know the outer core is liquid. | text | null |
L_0305 | seismic waves | T_1683 | Surface waves travel along the ground, outward from an earthquakes epicenter. Surface waves are the slowest of all seismic waves, traveling at 2.5 km (1.5 miles) per second. There are two types of surface waves. The rolling motions of surface waves do most of the damage in an earthquake. | text | null |
L_0306 | short term climate change | T_1684 | Short-term changes in climate are common and they have many causes (Figure 1.1). The largest and most important of these is the oscillation between El Nio and La Nia conditions. This cycle is called the ENSO (El Nio Southern Oscillation). The ENSO drives changes in climate that are felt around the world about every two to seven years. | text | null |
L_0306 | short term climate change | T_1685 | In a normal year, the trade winds blow across the Pacific Ocean near the Equator from east to west (toward Asia). A low pressure cell rises above the western equatorial Pacific. Warm water in the western Pacific Ocean raises sea levels by half a meter. Along the western coast of South America, the Peru Current carries cold water northward, and then westward along the Equator with the trade winds. Upwelling brings cold, nutrient-rich waters from the deep sea. | text | null |
L_0306 | short term climate change | T_1686 | In an El Nio year, when water temperature reaches around 28o C (82o F), the trade winds weaken or reverse direction and blow east (toward South America) (Figure 1.2). Warm water is dragged back across the Pacific Ocean and piles up off the west coast of South America. With warm, low-density water at the surface, upwelling stops. Without upwelling, nutrients are scarce and plankton populations decline. Since plankton form the base of the food web, fish cannot find food, and fish numbers decrease as well. All the animals that eat fish, including birds and humans, are affected by the decline in fish. By altering atmospheric and oceanic circulation, El Nio events change global climate patterns. Some regions receive more than average rainfall, including the west coast of North and South America, the southern United States, and Western Europe. Drought occurs in other parts of South America, the western Pacific, southern and northern Africa, and southern Europe. An El Nio cycle lasts one to two years. Often, normal circulation patterns resume. Sometimes circulation patterns bounce back quickly and extremely (Figure 1.3). This is a La Nia. | text | null |
L_0306 | short term climate change | T_1686 | In an El Nio year, when water temperature reaches around 28o C (82o F), the trade winds weaken or reverse direction and blow east (toward South America) (Figure 1.2). Warm water is dragged back across the Pacific Ocean and piles up off the west coast of South America. With warm, low-density water at the surface, upwelling stops. Without upwelling, nutrients are scarce and plankton populations decline. Since plankton form the base of the food web, fish cannot find food, and fish numbers decrease as well. All the animals that eat fish, including birds and humans, are affected by the decline in fish. By altering atmospheric and oceanic circulation, El Nio events change global climate patterns. Some regions receive more than average rainfall, including the west coast of North and South America, the southern United States, and Western Europe. Drought occurs in other parts of South America, the western Pacific, southern and northern Africa, and southern Europe. An El Nio cycle lasts one to two years. Often, normal circulation patterns resume. Sometimes circulation patterns bounce back quickly and extremely (Figure 1.3). This is a La Nia. | text | null |
L_0306 | short term climate change | T_1687 | In a La Nia year, as in a normal year, trade winds moves from east to west and warm water piles up in the western Pacific Ocean. Ocean temperatures along coastal South America are colder than normal (instead of warmer, as in El Nio). Cold water reaches farther into the western Pacific than normal. Other important oscillations are smaller and have a local, rather than global, effect. The North Atlantic Oscillation mostly alters climate in Europe. The Mediterranean also goes through cycles, varying between being dry at some times and warm and wet at others. Click image to the left or use the URL below. URL: | text | null |
L_0311 | solar energy on earth | T_1708 | Most of the energy that reaches the Earths surface comes from the Sun (Figure 1.1). About 44% of solar radiation is in the visible light wavelengths, but the Sun also emits infrared, ultraviolet, and other wavelengths. | text | null |
L_0311 | solar energy on earth | T_1709 | Of the solar energy that reaches the outer atmosphere, ultraviolet (UV) wavelengths have the greatest energy. Only about 7% of solar radiation is in the UV wavelengths. The three types are: UVC: the highest energy ultraviolet, does not reach the planets surface at all. UVB: the second highest energy, is also mostly stopped in the atmosphere. UVA: the lowest energy, travels through the atmosphere to the ground. | text | null |
L_0311 | solar energy on earth | T_1710 | The remaining solar radiation is the longest wavelength, infrared. Most objects radiate infrared energy, which we feel as heat. Some of the wavelengths of solar radiation traveling through the atmosphere may be lost because they are absorbed by various gases (Figure 1.2). Ozone completely removes UVC, most UVB, and some UVA from incoming sunlight. O2 , CO2 , and H2 O also filter out some wavelengths. An image of the Sun taken by the SOHO spacecraft. The sensor is picking up only the 17.1 nm wavelength, in the ultraviolet wavelengths. Atmospheric gases filter some wave- lengths of incoming solar energy. Yel- low shows the energy that reaches the top of the atmosphere. Red shows the wavelengths that reach sea level. Ozone filters out the shortest wavelength UV and oxygen filters out most infrared. Click image to the left or use the URL below. URL: | text | null |
L_0311 | solar energy on earth | T_1710 | The remaining solar radiation is the longest wavelength, infrared. Most objects radiate infrared energy, which we feel as heat. Some of the wavelengths of solar radiation traveling through the atmosphere may be lost because they are absorbed by various gases (Figure 1.2). Ozone completely removes UVC, most UVB, and some UVA from incoming sunlight. O2 , CO2 , and H2 O also filter out some wavelengths. An image of the Sun taken by the SOHO spacecraft. The sensor is picking up only the 17.1 nm wavelength, in the ultraviolet wavelengths. Atmospheric gases filter some wave- lengths of incoming solar energy. Yel- low shows the energy that reaches the top of the atmosphere. Red shows the wavelengths that reach sea level. Ozone filters out the shortest wavelength UV and oxygen filters out most infrared. Click image to the left or use the URL below. URL: | text | null |
L_0312 | solar power | T_1711 | Energy from the Sun comes from the lightest element, hydrogen, fusing together to create the second lightest element, helium. Nuclear fusion on the Sun releases tremendous amounts of solar energy. The energy travels to the Earth, mostly as visible light. The light carries the energy through the empty space between the Sun and the Earth as radiation. | text | null |
L_0312 | solar power | T_1712 | Solar energy has been used for power on a small scale for hundreds of years, and plants have used it for billions of years. Unlike energy from fossil fuels, which almost always come from a central power plant or refinery, solar power can be harnessed locally (Figure 1.1). A set of solar panels on a homes rooftop can be used to heat water for a swimming pool or can provide electricity to the house. Societys use of solar power on a larger scale is just starting to increase. Scientists and engineers have very active, ongoing research into new ways to harness energy from the Sun more efficiently. Because of the tremendous amount of incoming sunlight, solar power is being developed in the United States in southeastern California, Nevada, and Arizona. Solar panels supply power to the Interna- tional Space Station. Solar power plants turn sunlight into electricity using a large group of mirrors to focus sunlight on one place, called a receiver (Figure 1.2). A liquid, such as oil or water, flows through this receiver and is heated to a high temperature by the focused sunlight. The heated liquid transfers its heat to a nearby object that is at a lower temperature through a process called conduction. The energy conducted by the heated liquid is used to make electricity. This solar power plant uses mirrors to focus sunlight on the tower in the center. The sunlight heats a liquid inside the tower to a very high temperature, producing energy to make electricity. | text | null |
L_0312 | solar power | T_1712 | Solar energy has been used for power on a small scale for hundreds of years, and plants have used it for billions of years. Unlike energy from fossil fuels, which almost always come from a central power plant or refinery, solar power can be harnessed locally (Figure 1.1). A set of solar panels on a homes rooftop can be used to heat water for a swimming pool or can provide electricity to the house. Societys use of solar power on a larger scale is just starting to increase. Scientists and engineers have very active, ongoing research into new ways to harness energy from the Sun more efficiently. Because of the tremendous amount of incoming sunlight, solar power is being developed in the United States in southeastern California, Nevada, and Arizona. Solar panels supply power to the Interna- tional Space Station. Solar power plants turn sunlight into electricity using a large group of mirrors to focus sunlight on one place, called a receiver (Figure 1.2). A liquid, such as oil or water, flows through this receiver and is heated to a high temperature by the focused sunlight. The heated liquid transfers its heat to a nearby object that is at a lower temperature through a process called conduction. The energy conducted by the heated liquid is used to make electricity. This solar power plant uses mirrors to focus sunlight on the tower in the center. The sunlight heats a liquid inside the tower to a very high temperature, producing energy to make electricity. | text | null |
L_0312 | solar power | T_1713 | Solar energy has many benefits. It is extremely abundant, widespread, and will never run out. But there are problems with the widespread use of solar power. Sunlight must be present. Solar power is not useful in locations that are often cloudy or dark. However, storage technology is being developed. The technology needed for solar power is still expensive. An increase in interested customers will provide incentive for companies to research and develop new technologies and to figure out how to mass-produce existing technologies (Figure 1.3). Solar panels require a lot of space. Fortunately, solar panels can be placed on any rooftop to supply at least some of the power required for a home or business. This experimental car is one example of the many uses that engineers have found for solar energy. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0313 | star classification | T_1714 | Think about how the color of a piece of metal changes with temperature. A coil of an electric stove will start out black, but with added heat will start to glow a dull red. With more heat, the coil turns a brighter red, then orange. At extremely high temperatures the coil will turn yellow-white, or even blue-white (its hard to imagine a stove coil getting that hot). A stars color is also determined by the temperature of the stars surface. Relatively cool stars are red, warmer stars are orange or yellow, and extremely hot stars are blue or blue-white (Figure 1.1). | text | null |
L_0313 | star classification | T_1715 | Color is the most common way to classify stars. Table 1.1 shows the classification system. The class of a star is given by a letter. Each letter corresponds to a color, and also to a range of temperatures. Note that these letters dont match the color names; they are left over from an older system that is no longer used. Class O B A F G K M Color Blue Blue-white White Yellowish-white Yellow Orange Red Temperature Range 30,000 K or more 10,000-30,000 K 7,500-10,000 K 6,000-7,500 K 5,500-6,000 K 3,500-5,000 K 2,000-3,500 K Sample Star Zeta Ophiuchi Rigel Altair Procyon A Sun Epsilon Indi Betelgeuse, Proxima Cen- tauri For most stars, surface temperature is also related to size. Bigger stars produce more energy, so their surfaces are hotter. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0314 | star constellations | T_1716 | When you look at the sky on a clear night, you can see dozens, perhaps even hundreds, of tiny points of light. Almost every one of these points of light is a star, a giant ball of glowing gas at a very, very high temperature. Stars differ in size, temperature, and age, but they all appear to be made up of the same elements and to behave according to the same principles. | text | null |
L_0314 | star constellations | T_1717 | People of many different cultures, including the Greeks, identified patterns of stars in the sky. We call these patterns constellations. Figure 1.1 shows one of the most easily recognized constellations. Why do the patterns in constellations and in groups or clusters of stars, called asterisms, stay the same night after night? Although the stars move across the sky, they stay in the same patterns. This is because the apparent nightly motion of the stars is actually caused by the rotation of Earth on its axis. The patterns also shift in the sky with the seasons as Earth revolves around the Sun. As a result, people in a particular location can see different constellations in the winter than in the summer. For example, in the Northern Hemisphere Orion is a prominent constellation in the winter sky, but not in the summer sky. This is the annual traverse of the constellations. | text | null |
L_0314 | star constellations | T_1718 | Although the stars in a constellation appear close together as we see them in our night sky, they are not at all close together out in space. In the constellation Orion, the stars visible to the naked eye are at distances ranging from just 26 light-years (which is relatively close to Earth) to several thousand light-years away. Click image to the left or use the URL below. URL: | text | null |
L_0314 | star constellations | T_1719 | There is no reason to think that the alignment of the stars has anything to do with events that happen on Earth. The constellations were defined by people who noticed that patterns could be made from stars, but the patterns do not reflect any characteristics of the stars themselves. When scientific tests are done to provide evidence in support of astrological ideas, the tests fail. When a scientific idea fails, it is abandoned or modified. Astrologers do not change or abandon their ideas. Click image to the left or use the URL below. URL: | text | null |
L_0315 | star power | T_1720 | The Sun is Earths major source of energy, yet the planet only receives a small portion of its energy. The Sun is just an ordinary star. Many stars produce much more energy than the Sun. The energy source for all stars is nuclear fusion. | text | null |
L_0315 | star power | T_1721 | Stars are made mostly of hydrogen and helium, which are packed so densely in a star that in the stars center the pressure is great enough to initiate nuclear fusion reactions. In a nuclear fusion reaction, the nuclei of two atoms combine to create a new atom. Most commonly, in the core of a star, two hydrogen atoms fuse to become a helium atom. Although nuclear fusion reactions require a lot of energy to get started, once they are going they produce enormous amounts of energy (Figure 1.1). In a star, the energy from fusion reactions in the core pushes outward to balance the inward pull of gravity. This energy moves outward through the layers of the star until it finally reaches the stars outer surface. The outer layer of the star glows brightly, sending the energy out into space as electromagnetic radiation, including visible light, heat, ultraviolet light, and radio waves (Figure 1.2). | text | null |
L_0315 | star power | T_1722 | In particle accelerators, subatomic particles are propelled until they have attained almost the same amount of energy as found in the core of a star (Figure 1.3). When these particles collide head-on, new particles are created. This process simulates the nuclear fusion that takes place in the cores of stars. The process also simulates the conditions A diagram of a star like the Sun. that allowed for the first helium atom to be produced from the collision of two hydrogen atoms in the first few minutes of the universe. The SLAC National Accelerator Lab in California can propel particles a straight 2 mi (3.2 km). The CERN Particle Accelerator presented in this video is the worlds largest and most powerful particle accelerator. The accelerator can boost subatomic particles to energy levels that simulate conditions in the stars and in the early history of the universe before stars formed. Click image to the left or use the URL below. URL: | text | null |
L_0315 | star power | T_1722 | In particle accelerators, subatomic particles are propelled until they have attained almost the same amount of energy as found in the core of a star (Figure 1.3). When these particles collide head-on, new particles are created. This process simulates the nuclear fusion that takes place in the cores of stars. The process also simulates the conditions A diagram of a star like the Sun. that allowed for the first helium atom to be produced from the collision of two hydrogen atoms in the first few minutes of the universe. The SLAC National Accelerator Lab in California can propel particles a straight 2 mi (3.2 km). The CERN Particle Accelerator presented in this video is the worlds largest and most powerful particle accelerator. The accelerator can boost subatomic particles to energy levels that simulate conditions in the stars and in the early history of the universe before stars formed. Click image to the left or use the URL below. URL: | text | null |
L_0316 | states of water | T_1723 | Water is simply two atoms of hydrogen and one atom of oxygen bonded together (Figure 1.1). The hydrogen ions are on one side of the oxygen ion, making water a polar molecule. This means that one side, the side with the hydrogen ions, has a slightly positive electrical charge. The other side, the side without the hydrogen ions, has a slightly negative charge. Despite its simplicity, water has remarkable properties. Water expands when it freezes, has high surface tension (because of the polar nature of the molecules, they tend to stick together), and others. Without water, life might not be able to exist on Earth and it certainly would not have the tremendous complexity and diversity that we see. | text | null |
L_0316 | states of water | T_1724 | Water is the only substance on Earth that is present in all three states of matter - as a solid, liquid or gas. (And Earth is the only planet where water is abundantly present in all three states.) Because of the ranges in temperature in specific locations around the planet, all three phases may be present in a single location or in a region. The three phases are solid (ice or snow), liquid (water), and gas (water vapor). See ice, water, and clouds (Figure 1.2). (a) Ice floating in the sea. Can you find all three phases of water in this image? (b) Liquid water. (c) Water vapor is invisible, but clouds that form when water vapor condenses are not. Click image to the left or use the URL below. URL: | text | null |
L_0316 | states of water | T_1724 | Water is the only substance on Earth that is present in all three states of matter - as a solid, liquid or gas. (And Earth is the only planet where water is abundantly present in all three states.) Because of the ranges in temperature in specific locations around the planet, all three phases may be present in a single location or in a region. The three phases are solid (ice or snow), liquid (water), and gas (water vapor). See ice, water, and clouds (Figure 1.2). (a) Ice floating in the sea. Can you find all three phases of water in this image? (b) Liquid water. (c) Water vapor is invisible, but clouds that form when water vapor condenses are not. Click image to the left or use the URL below. URL: | text | null |
L_0318 | stratosphere | T_1729 | There is little mixing between the stratosphere, the layer above the troposphere, and the troposphere below it. The two layers are quite separate. Sometimes ash and gas from a large volcanic eruption may burst into the stratosphere. Once in the stratosphere, it remains suspended there for many years because there is so little mixing between the two layers. | text | null |
L_0318 | stratosphere | T_1730 | In the stratosphere, temperature increases with altitude. What is the heat source for the stratosphere? The direct heat source for the stratosphere is the Sun. The ozone layer in the stratosphere absorbs high energy ultraviolet radiation, which breaks the ozone molecule (3-oxygens) apart into an oxygen molecule (2-oxygens) and an oxygen atom (1- oxygen). In the mid-stratosphere there is less UV light and so the oxygen atom and molecule recombine to from ozone. The creation of the ozone molecule releases heat. Because warmer, less dense air sits over cooler, denser air, air in the stratosphere is stable. As a result, there is little mixing of air within the layer. There is also little interaction between the troposphere and stratosphere for this reason. | text | null |
L_0318 | stratosphere | T_1731 | The ozone layer is found within the stratosphere between 15 to 30 km (9 to 19 miles) altitude. The ozone layer has a low concentration of ozone; its just higher than the concentration elsewhere. The thickness of the ozone layer varies by the season and also by latitude. Ozone is created in the stratosphere by solar energy. Ultraviolet radiation splits an oxygen molecule into two oxygen atoms. One oxygen atom combines with another oxygen molecule to create an ozone molecule, O3 . The ozone is unstable and is later split into an oxygen molecule and an oxygen atom. This is a natural cycle that leaves some ozone in the stratosphere. The ozone layer is extremely important because ozone gas in the stratosphere absorbs most of the Suns harmful ultraviolet (UV) radiation. Because of this, the ozone layer protects life on Earth. High-energy UV light penetrates cells and damages DNA, leading to cell death (which we know as a bad sunburn). Organisms on Earth are not adapted to heavy UV exposure, which kills or damages them. Without the ozone layer to absorb UVC and UVB radiation, most complex life on Earth would not survive long. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: | text | null |
L_0319 | streams and rivers | T_1732 | Streams are bodies of water that have a current; they are in constant motion. Geologists recognize many categories of streams depending on their size, depth, speed, and location. Creeks, brooks, tributaries, bayous, and rivers are all streams. In streams, water always flows downhill, but the form that downhill movement takes varies with rock type, topography, and many other factors. Stream erosion and deposition are extremely important creators and destroyers of landforms. Rivers are the largest streams. People have used rivers since the beginning of civilization as a source of water, food, transportation, defense, power, recreation, and waste disposal. With its high mountains, valleys and Pacific coastline, the western United States exhibits nearly all of the features common to rivers and streams. The photos below are from the western states of Montana, California and Colorado. | text | null |
L_0319 | streams and rivers | T_1733 | A stream originates at its source. A source is likely to be in the high mountains where snows collect in winter and melt in summer, or a source might be a spring. A stream may have more than one source. Two streams come together at a confluence. The smaller of the two streams is a tributary of the larger stream (Figure 1.1). The confluence between the Yellowstone River and one of its tributaries, the Gar- diner River, in Montana. The point at which a stream comes into a large body of water, like an ocean or a lake, is called the mouth. Where the stream meets the ocean or lake is an estuary (Figure 1.2). The mouth of the Klamath River creates an estuary where it flows into the Pacific Ocean in California. The mix of fresh and salt water where a river runs into the ocean creates a diversity of environments where many different types of organisms create unique ecosystems. | text | null |
L_0319 | streams and rivers | T_1733 | A stream originates at its source. A source is likely to be in the high mountains where snows collect in winter and melt in summer, or a source might be a spring. A stream may have more than one source. Two streams come together at a confluence. The smaller of the two streams is a tributary of the larger stream (Figure 1.1). The confluence between the Yellowstone River and one of its tributaries, the Gar- diner River, in Montana. The point at which a stream comes into a large body of water, like an ocean or a lake, is called the mouth. Where the stream meets the ocean or lake is an estuary (Figure 1.2). The mouth of the Klamath River creates an estuary where it flows into the Pacific Ocean in California. The mix of fresh and salt water where a river runs into the ocean creates a diversity of environments where many different types of organisms create unique ecosystems. | text | null |
L_0319 | streams and rivers | T_1734 | As a stream flows from higher elevations, like in the mountains, towards lower elevations, like the ocean, the work of the stream changes. At a streams headwaters, often high in the mountains, gradients are steep (Figure 1.3). The stream moves fast and does lots of work eroding the stream bed. Headwaters of the Roaring Fork River in Colorado. As a stream moves into lower areas, the gradient is not as steep. Now the stream does more work eroding the edges of its banks. Many streams develop curves in their channels called meanders (Figure 1.4). As the river moves onto flatter ground, the stream erodes the outer edges of its banks to carve a floodplain, which is a flat, level area surrounding the stream channel (Figure 1.5). Base level is where a stream meets a large body of standing water, usually the ocean, but sometimes a lake or pond. Streams work to down cut in their stream beds until they reach base level. The higher the elevation, the farther the stream is from where it will reach base level and the more cutting it has to do. The ultimate base level is sea level. | text | null |
L_0319 | streams and rivers | T_1734 | As a stream flows from higher elevations, like in the mountains, towards lower elevations, like the ocean, the work of the stream changes. At a streams headwaters, often high in the mountains, gradients are steep (Figure 1.3). The stream moves fast and does lots of work eroding the stream bed. Headwaters of the Roaring Fork River in Colorado. As a stream moves into lower areas, the gradient is not as steep. Now the stream does more work eroding the edges of its banks. Many streams develop curves in their channels called meanders (Figure 1.4). As the river moves onto flatter ground, the stream erodes the outer edges of its banks to carve a floodplain, which is a flat, level area surrounding the stream channel (Figure 1.5). Base level is where a stream meets a large body of standing water, usually the ocean, but sometimes a lake or pond. Streams work to down cut in their stream beds until they reach base level. The higher the elevation, the farther the stream is from where it will reach base level and the more cutting it has to do. The ultimate base level is sea level. | text | null |
L_0319 | streams and rivers | T_1735 | A divide is a topographically high area that separates a landscape into different water basins (Figure 1.6). Rain that falls on the north side of a ridge flows into the northern drainage basin and rain that falls on the south side flows into the southern drainage basin. On a much grander scale, entire continents have divides, known as continental divides. A green floodplain surrounds the Red Rock River as it flows through Montana. (a) The divides of North America. In the Rocky Mountains in Colorado, where does a raindrop falling on the western slope end up? How about on the eastern slope? (b) At Triple Divide Peak in Montana water may flow to the Pacific, the Atlantic, or Hudson Bay depending on where it falls. Can you locate where in the map of North America this peak sits? | text | null |
L_0319 | streams and rivers | T_1735 | A divide is a topographically high area that separates a landscape into different water basins (Figure 1.6). Rain that falls on the north side of a ridge flows into the northern drainage basin and rain that falls on the south side flows into the southern drainage basin. On a much grander scale, entire continents have divides, known as continental divides. A green floodplain surrounds the Red Rock River as it flows through Montana. (a) The divides of North America. In the Rocky Mountains in Colorado, where does a raindrop falling on the western slope end up? How about on the eastern slope? (b) At Triple Divide Peak in Montana water may flow to the Pacific, the Atlantic, or Hudson Bay depending on where it falls. Can you locate where in the map of North America this peak sits? | text | null |
L_0320 | supervolcanoes | T_1736 | Supervolcano eruptions are extremely rare in Earths history. Its a good thing because they are unimaginably large. A supervolcano must erupt more than 1,000 cubic km (240 cubic miles) of material, compared with 1.2 km3 for Mount St. Helens or 25 km3 for Mount Pinatubo, a large eruption in the Philippines in 1991. Not surprisingly, supervolcanoes are the most dangerous type of volcano. | text | null |
L_0320 | supervolcanoes | T_1737 | The exact cause of supervolcano eruptions is still debated. However, scientists think that a very large magma chamber erupts entirely in one catastrophic explosion. This creates a huge hole or caldera into which the surface collapses (Figure 1.1). The caldera at Santorini in Greece is so large that it can only be seen by satellite. | text | null |
L_0320 | supervolcanoes | T_1738 | The largest supervolcano in North America is beneath Yellowstone National Park in Wyoming. Yellowstone sits above a hotspot that has erupted catastrophically three times: 2.1 million, 1.3 million, and 640,000 years ago. Yellowstone has produced many smaller (but still enormous) eruptions more recently (Figure 1.2). Fortunately, current activity at Yellowstone is limited to the regions famous geysers. Click image to the left or use the URL below. URL: The Yellowstone hotspot has produced enormous felsic eruptions. The Yellowstone caldera collapsed in the most recent super eruption. | text | null |
L_0320 | supervolcanoes | T_1739 | A supervolcano could change life on Earth as we know it. Ash could block sunlight so much that photosynthesis would be reduced and global temperatures would plummet. Volcanic eruptions could have contributed to some of the mass extinctions in our planets history. No one knows when the next super eruption will be. Interesting volcano videos are seen on National Geographic Videos, Environment Video, Natural Disasters, Earth- quakes: One interesting one is Mammoth Mountain, which explores Hot Creek and the volcanic area it is a part of in California. Click image to the left or use the URL below. URL: | text | null |
L_0321 | surface features of the sun | T_1740 | The Suns surface features are quite visible, but only with special equipment. For example, sunspots are only visible with special light-filtering lenses. | text | null |
L_0321 | surface features of the sun | T_1741 | The most noticeable surface features of the Sun are cooler, darker areas known as sunspots (Figure 1.1). Sunspots are located where loops of the Suns magnetic field break through the surface and disrupt the smooth transfer of heat from lower layers of the Sun, making them cooler, darker, and marked by intense magnetic activity. Sunspots usually occur in pairs. When a loop of the Suns magnetic field breaks through the surface, a sunspot is created where the loop comes out and where it goes back in again. Sunspots usually occur in 11-year cycles, increasing from a minimum number to a maximum number and then gradually decreasing to a minimum number again. | text | null |
L_0321 | surface features of the sun | T_1742 | There are other types of interruptions of the Suns magnetic energy. If a loop of the Suns magnetic field snaps and breaks, it creates solar flares, which are violent explosions that release huge amounts of energy (Figure 1.2). A strong solar flare can turn into a coronal mass ejection. A solar flare or coronal mass ejection releases streams of highly energetic particles that make up the solar wind. The solar wind can be dangerous to spacecraft and astronauts because it sends out large amounts of radiation that can harm the human body. Solar flares have knocked out entire power grids and disturbed radio, satellite, and cell phone communications. (a) Sunspots. (b) A close-up of a sunspot taken in ultraviolet light. | text | null |
L_0321 | surface features of the sun | T_1742 | There are other types of interruptions of the Suns magnetic energy. If a loop of the Suns magnetic field snaps and breaks, it creates solar flares, which are violent explosions that release huge amounts of energy (Figure 1.2). A strong solar flare can turn into a coronal mass ejection. A solar flare or coronal mass ejection releases streams of highly energetic particles that make up the solar wind. The solar wind can be dangerous to spacecraft and astronauts because it sends out large amounts of radiation that can harm the human body. Solar flares have knocked out entire power grids and disturbed radio, satellite, and cell phone communications. (a) Sunspots. (b) A close-up of a sunspot taken in ultraviolet light. | text | null |
L_0321 | surface features of the sun | T_1743 | Another highly visible feature on the Sun are solar prominences. If plasma flows along a loop of the Suns magnetic field from sunspot to sunspot, it forms a glowing arch that reaches thousands of kilometers into the Suns atmosphere. Prominences can last lengths of time ranging from a day to several months. Prominences are also visible during a total solar eclipse. Most of the imagery comes from SDOs AIA instrument; different colors represent different temperatures, a common technique for observing solar features. SDO sees the entire disk of the Sun in extremely high spatial and temporal resolution, allowing scientists to zoom in on notable events such as flares, waves, and sunspots. | text | null |
L_0321 | surface features of the sun | T_1744 | The video above was taken from the SDO, the most advanced spacecraft ever designed to study the Sun. During its five-year mission, SDO will examine the Suns magnetic field and also provide a better understanding of the role the Sun plays in Earths atmospheric chemistry and climate. Since just after its launch on February 11, 2010, SDO is providing images with clarity 10 times better than high-definition television and will return more comprehensive science data faster than any other solar-observing spacecraft. The Solar Dynamics Observatory is a NASA spacecraft launched in early 2010 is obtaining IMAX-like images of the Sun every second of the day, generating more data than any NASA mission in history. The data will allow researchers to learn about solar storms and other phenomena that can cause blackouts and harm astronauts. Click image to the left or use the URL below. URL: | text | null |
L_0323 | sustainable development | T_1750 | Can society change and get on a sustain- able path? A topic generating a great deal of discussion these days is sustainable development. The goals of sustainable development are to: help people out of poverty. protect the environment. use resources no faster than the rate at which they are regenerated. Science can be an important part of sustainable development. When scientists understand how Earths natural systems work, they can recognize how people are impacting them. Scientists can work to develop technologies that can be used to solve problems wisely. An example of a practice that can aid sustainable development is fish farming, as long as it is done in environmentally sound ways. Engineers can develop cleaner energy sources to reduce pollution and greenhouse gas emissions. Citizens can change their behavior to reduce the impact they have on the planet by demanding products that are produced sustainably. When forests are logged, new trees should be planted. Mining should be done so that the landscape is not destroyed. People can consume less and think more about the impacts of what they do consume. And what of the waste products of society? Will producing all that we need to keep the population growing result in a planet so polluted that the quality of life will be greatly diminished? Will warming temperatures cause problems for human populations? The only answer to all of these questions is, time will tell. Click image to the left or use the URL below. URL: | text | null |
L_0326 | testing hypotheses | T_1757 | How do you test a hypothesis? In this example, we will look into the scientific literature to find data in studies that were done using scientific method. To test Hypothesis 1 from the concept "Development of Hypotheses," we need to see if the amount of CO2 gas released by volcanoes over the past several decades has increased. There are two ways volcanoes could account for the increase in CO2 : There has been an increase in volcanic eruptions in that time. The CO2 content of volcanic gases has increased over time globally. To test the first hypothesis, we look at the scientific literature. We see that the number of volcanic eruptions is about constant. We also learn from the scientific literature that volcanic gas compositions have not changed over time. Different types of volcanoes have different gas compositions, but overall the gases are the same. Another journal article states that major volcanic eruptions for the past 30 years have caused short-term cooling, not warming! Hypothesis 1 is wrong! Volcanic activity is not able to account for the rise in atmospheric CO2 . Remember that science is falsifiable. We can discard Hypothesis 1. | text | null |
L_0326 | testing hypotheses | T_1758 | Hypothesis 2 states that the increase in atmospheric CO2 is due to the increase in the amount of fossil fuels that are being burned. We look into the scientific literature and find this graph in the Figure 1.1. Global carbon dioxide emissions from fos- sil fuel consumption and cement produc- tion. The black line represents all emis- sion types combined, and colored lines show emissions from individual fossil fu- els. Fossil fuels have added an increasing amount of carbon dioxide to the atmosphere since the beginning of the Industrial Revolution in the mid 19th century. Hypothesis 2 is true! Click image to the left or use the URL below. URL: | text | null |
L_0327 | the hertzsprung russell diagra | T_1759 | The Hertzsprung-Russell diagram (often referred to as the H-R diagram) is a scatter graph that shows various classes of stars in the context of properties such as their luminosity, absolute magnitude, color, and effective temperature. Created around 1910 by Ejnar Hertzsprung and Henry Norris Russell, the diagram provided a great help in understanding stellar evolution. There are several forms of the Hertzsprung-Russell diagram, and the nomenclature is not very well defined. The original diagram displayed the spectral type of stars on the horizontal axis and the absolute magnitude on the vertical axis. The form below shows Kelvin temperature along the horizontal axis going from high temperature on the left to low temperature on the right and luminosity on the vertical axis. We can think of the luminosity as brightness in multiples of the Sun. A luminosity of 100 on the axis would mean 100 times as bright as the Sun. Most of the stars occupy a region in the diagram along a line called the Main Sequence. During that stage, stars are fusing hydrogen into helium in their cores. The position of the Sun in the main sequence is shown in the diagram. You should note that the axial scales for this diagram are not linear. The vertical scale is logarithmic, each line is 100 times greater than the previous line. On the horizontal axis, as we move to the right, the temperature reduces by between 1,000 and 10,000 degrees K between each line. If all other factors were the same, the highest temperature stars would also be the most luminous (the brightest). In the main sequence of stars, we see that as the temperature increases to the left, the luminosity also increases, demonstrating that the hottest stars in this grouping are also the brightest. There are stars, however, that are less bright than their temperature would predict. This group of stars is called white dwarfs. These stars are less bright than expected because of their very small size. These dwarf stars are only one one-thousandth the size of stars in the main sequence. There are also stars that are much brighter than their temperature would predict. This group of stars are called red giants. They are brighter than their temperature would predict because they are much larger than stars in the main sequence. These stars have expanded to several thousand times the size of stars in the main sequence. Stars that are reddish in color are cooler than other stars while stars that are bluish in color are hotter than other stars. A white dwarf is a stellar remnant that is very dense. A white dwarfs mass is comparable to the Sun and its volume is comparable to that of Earth. The very low brightness of a white dwarf comes from the emission of stored heat energy. White dwarfs are thought to be the final evolutionary state of any star whose mass is not great enough to become a neutron star. Approximately 97% of the stars in our galaxy will become neutron stars. After the hydrogen-fusing lifetime of a main-sequence star of low or medium mass ends, it will expand to a red giant which fuses helium to carbon and oxygen in its core. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon, around 1 billion K, an inert mass of carbon and oxygen will build up at its center. After blowing off its outer layers to form a planetary nebula, the core will be left behind to form the remnant white dwarf. White dwarfs are composed of carbon and oxygen. A white dwarf is very hot when it is formed, but since it has no source of energy (no further fusion reactions), it will gradually radiate away its energy and cool down. Over a very long time, a white dwarf will cool to temperatures at which it will no longer emit significant light, and it will become a cold black dwarf. A red giant star is a star with a mass like the Sun that is in the last phase of its life, when Hydrogen fusion reactions in the core decrease due to the lack of fuel. With the gravitational collapse of the core, the fusion reactions now occur in a shell surrounding the core. The outer layer of the star expands enormously up to 1000 times the size of the Sun. When the Sun becomes a red giant, its volume will include the orbit of Mercury and Venus and maybe even Earth. The increased size increases the luminosity even though the outer layer cools to only 3000 K or so. The cooler outer layer causes it to be a red star. After a few more million years, the star evolves into a white dwarf-planetary nebula system. | text | null |
L_0328 | the history of astronom | T_1761 | The Astronomy of the ancient Greeks was linked to mathematics, and Greek astronomers sought to create geomet- rical models that could imitate the appearance of celestial motions. This tradition originated around the 6th century BCE, with the followers of the mathematician Pythagoras (~580 - 500 BCE). Pythagoras believed that everything was related to mathematics and that through mathematics everything could be predicted and measured in rhythmic patterns or cycles. He placed astronomy as one of the four mathematical arts, the others being arithmetic, geometry and music. While best known for the Pythagorean Theorem, Pythagoras did have some input into astronomy. By the time of Pythagoras, the five planets visible to the naked eye - Mercury, Venus, Mars, Jupiter and Saturn - had long been identified. The names of these planets were initially derived from Greek mythology before being given the equivalent Roman mythological names, which are the ones we still use today. The word planet is a Greek term meaning wanderer, as these bodies move across the sky at different speeds from the stars, which appear fixed in the same positions relative to each other. For part of the year Venus appears in the eastern sky as an early morning object before disappearing and reappearing a few weeks later in the evening western sky. Early Greek astronomers thought this was two different bodies and assigned the names Phosphorus and Hesperus to the morning and evening apparitions respectively. Pythagoras is given credit for being the first to realize that these two bodies were in fact the same planet, a notion he arrived at through observation and geometrical calculations. Pythagoras was also one of the first to think that the Earth was round, a theory that was finally proved around 330 BCE by Aristotle. (Although, as you are probably aware, many people in 1642 CE still believed the earth to be flat.) Aristotle (384 BCE - 322 BCE) demonstrates in his writings that he knew we see the moon by the light of the sun, how the phases of the moon occur, and understood how eclipses work. He also knew that the earth was a sphere. Philosophically, he argued that each part of the earth is trying to be pulled to the center of the earth, and so the earth would naturally take on a spherical shape. He then pointed out observations that support the idea of a spherical earth. First, the shadow of the earth on the moon during a lunar eclipse is always circular. The only shape that always casts a circular shadow is a sphere. Second, as one traveles more north or south, the positions of the stars in the sky change. There are constellations visible in the north that one cannot see in the south and vice versa. He related this to the curvature of the earth. Aristotle talked about the work of earlier Greeks, who had developed an earth centered model of the planets. In these models, the center of the earth is the center of all the other motions. While it is not sure if the earlier Greeks actually thought the planets moved in circles, it is clear that Aristotle did. Aristotle rejected a moving earth for two reasons. Most importantly he didnt understand inertia. To Aristotle, the natural state for an object was to be at rest. He believed that it takes a force in order for an object to move. Using Aristotles ideas, if the earth were moving through space, if you tripped, you would not be in contact with the earth, and so would get left behind in space. Since this obviously does not happen, the earth must not move. This misunderstanding of inertia confused scientists until the time of Galileo. A second, but not as important, reason Aristotle rejected a moving earth is that he recognized that if the earth moved and rotated around the sun, there would be an observable parallax of the stars. One cannot see stellar parallax with the naked-eye, so Aristotle concluded that the earth must be at rest. (The stars are so far away, that one needs a good telescope to measure stellar parallax, which was first measured in 1838.) Aristotle believed that the objects in the heavens are perfect and unchanging. Since he believed that the only eternal motion is circular with a constant speed, the motions of the planets must be circular. This came to be called The Principal of Uniform Circular Motion. Aristotle and his ideas became very important because they became incorporated into the Catholic Churchs theology in the twelfth century by Thomas Aquinas. In the early 16th century, the Church banned new interpretations of scripture and this included a ban on ideas of a moving earth. Claudius Ptolemy (90 - 168 CE) was a citizen of Egypt which was under Roman rule during Ptolemys lifetime. During his lifetime he was a mathematician, astronomer, and geographer. His theories dominated the worlds understanding of astronomy for over a thousand years. While it is known that many astronomers published works during this time, only Ptolemys work The Almagest survived. In it, he outlined his geometrical reasoning for a geocentric view of the Universe. As outlined in the Almagest, the Universe according to Ptolemy was based on five main points: 1) the celestial realm is spherical, 2) the celestial realm moves in a circle, 3) the earth is a sphere, 4) the celestial realm orbit is a circle centered on the earth, and 5) earth does not move. Ptolemy also identified eight circular orbits surrounding earth where the other planets existed. In order, they were the moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn, and the sphere of fixed stars. A serious problem with the earth-centered system was the fact that at certain times in their orbits, some of the planets appeared to move in the opposite direction of their normal movement. This reverse direction movement is referred to as retrograde motion. If the earth was to remain motionless at the center of the system, some very intricate designs were necessary to explain the movement of the retrograde planets. In the Ptolemaic system, each retrograde planet moved by two spheres. The Ptolemaic system had circles within circles that produced epicycles. In the sketch above on the left, the red ball moved clockwise in its little circle while the entire orbit also orbited clockwise around the big circle. This process produced a path like that shown in the sketch above on the right. As the red ball moved around its path, at some times it would be moving clockwise and then for a short period, it would move counterclockwise. This motion was able to explain the retrograde motion noted for some planets. | text | null |
L_0328 | the history of astronom | T_1762 | It was not until 1543, when Copernicus (1473 - 1543) introduced a sun-centered design (heliocentric), that Ptolemys astronomy was seriously questioned and eventually overthrown. Copernicus studied at the University of Bologna, where he lived in the same house as the principal astronomer there. Copernicus assisted the astronomer in some of his observations and in the production of the annual astrological forecasts for the city. It is at Bologna that he probably first encountered a translation of Ptolemys Almagest that would later make it possible for Copernicus to successfully refute the ancient astronomer. Later, at the University of Padua, Copernicus studied medicine, which was closely associated with astrology at that time due to the belief that the stars influenced the dispositions of the body. Returning to Poland, Copernicus secured a teaching post at Wroclaw, where he primarily worked as a medical doctor and manager of Church affairs. In his spare time, he studied the stars and the planets (decades before the telescope was invented), and applied his mathematical understanding to the mysteries of the night sky. In so doing, he developed his theory of a system in which the Earth, like all the planets, revolved around the sun, and which simply and elegantly explained the curious retrograde movements of the planets. Copernicus wrote his theory in De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Orbs). The book was completed in 1530 or so, but it wasnt published until the year he died, 1543. It has been suggested that Copernicus knew the publication would incur the wrath of the Catholic church and he didnt want to deal with problems so he didnt publish his theory until he was on his death bed. Legend has it that a copy of the printers proof was placed in his hands as he lay in a coma, and he woke long enough to recognize what he was holding before he died. Tycho Brahe (1546 - 1601) was born in a part of southern Sweden that was part of Denmark at the time. While attending the university to study law and philosophy, he became interested in astronomy and spent most evenings observing the stars. One of Tycho Brahes first contributions to astronomy was the detection and correction of several serious errors in the standard astronomical tables. Then, in 1572, he discovered a supernova located in the constellation of Cassiopeia. Tycho built his own instruments and made the most complete and accurate observations available without the use of a telescope. Eventually, his fame led to an offer from King Frederick II of Denmark & Norway to fund the construction of an astronomical observatory. The island of Van was chosen and in 1576, construction began. Tycho Brahe spent twenty years there, making observations on celestial bodies. During his life, Tycho Brahe did not accept Copernicus model of the universe. He attempted to combine it with the Ptolemaic model. As a theoretician, Tycho was a failure but his observations and the data he collected was far superior to any others made prior to the invention of the telescope. After Tycho Brahes death, his assistant, Johannes Kepler used Tycho Brahes observations to calculate his own three laws of planetary motion. In 1600, Johannes Kepler (1571 - 1630) began working as Tychos assistant. They recognized that neither the Ptolemaic (geocentric) or Copernican (heliocentric) models could predict positions of Mars as accurately as they could measure them. Tycho died in 1601 and after that Kepler had full access to Tychos data. He analyzed the data for 8 years and tried to calculate an orbit that would fit the data, but was unable to do so. Kepler later determined that the orbits were not circular but elliptical. | text | null |
L_0328 | the history of astronom | T_1763 | 1. The orbits of the planets are elliptical. 2. An imaginary line connecting a planet and the sun sweeps out equal areas during equal time intervals. (Therefore, the earths orbital speed varies at different times of the year. The earth moves fastest in its orbit when closest to the sun and slowest when farthest away.) Keplers Second Law of Planetary Motion was calculated for Earth, then the hypothesis was tested using data for Mars, and it worked! 3. Keplers Third Law of Planetary Motion showed the relationship between the size of a planets orbit radius, R ( 12 the major axis), and its orbital period, T . R2 = T 3 This law is true for all planets if you use astronomical units (that is, distance in multiples of earths orbital radium and time in multiples of earth years). Keplers three laws replaced the cumbersome epicycles to explain planetary motion with three mathematical laws that allowed the positions of the planets to be predicted with accuracies ten times better than Ptolemaic or Copernican models. | text | null |
L_0328 | the history of astronom | T_1764 | Galileo Galilei (1564-1642) was a very important person in the development of modern astronomy, both because of his contributions directly to astronomy, and because of his work in physics. He provided the crucial observations that proved the Copernican hypothesis, and also laid the foundations for a correct understanding of how objects moved on the surface of the earth and of gravity. One could, with considerable justification, view Galileo as the father both of modern astronomy and of modern physics. Galileo did not invent the telescope, but he was the first to turn his telescope toward the sky to study the heavens systematically. His telescope was poorer than even a cheap modern amateur telescope, but what he observed in the heavens showed errors in Aristotles opinion of the universe and the worldview that it supported. Observations through Galileos telescope made it clear that the earth-centered and earth doesnt move solar system of Aristotle was incorrect. Since church officials had made some of Aristotles opinions a part of the religious views of the church, proving Aristotles views to be incorrect also pointed out flaws in the church. Galileo observed four points of light that changed their positions around the planet Jupiter and he concluded that these were moons in orbit around Jupiter. These observations showed that there were new things in the heavens that Aristotle and Ptolemy had known nothing about. Furthermore, they demonstrated that a planet could have moons circling it that would not be left behind as the planet moved around its orbit. One of the arguments against the Copernican system had been that if the moon were in orbit around the Earth and the Earth in orbit around the Sun, the Earth would leave the Moon behind as it moved around its orbit. Galileo used his telescope to show that Venus, like the moon, went through a complete set of phases. This observation was extremely important because it was the first observation that was consistent with the Copernican system but not the Ptolemaic system. In the Ptolemaic system, Venus should always be in crescent phase as viewed from the Earth because the sun is beyond Venus, but in the Copernican system Venus should exhibit a complete set of phases over time as viewed from the Earth because it is illuminated from the center of its orbit. It is important to note that this was the first empirical evidence (coming almost a century after Copernicus) that allowed a definitive test of the two models. Until that point, both the Ptolemaic and Copernican models described the available data. The primary attraction of the Copernican system was that it described the data in a simpler fashion, but here finally was conclusive evidence that not only was the Ptolemaic universe more complicated, it also was incorrect. As each new observation was brought to light, increasing doubt was cast on the old views of the heavens. It also raised the credibility issue: could the authority of Aristotle and Ptolemy be trusted concerning the nature of the Universe if there were so many things in the Universe about which they had been unaware and/or incorrect? Galileos challenge of the Churchs authority through his refutation of the Aristotelian concept of the Universe eventually got him into deep trouble. Late in his life he was forced, under threat of torture, to publicly recant his Copernican views and spent his last years under house arrest. Galileos life is a sad example of the conflict between the scientific method and unquestioned authority. Sir Isaac Newton (1642-1727), who was born the same year that Galileo died, would build on Galileos ideas to demonstrate that the laws of motion in the heavens and the laws of motion on the earth were the same. Thus Galileo began, and Newton completed, a synthesis of astronomy and physics in which astronomy was recognized as but a part of physics, and that the opinions of Aristotle were almost completely eliminated from both. Many scientists consider Newton to be a peer of Einstein in scientific thinking. Newtons accomplishments had even greater scope than those of Einstein. The poet Alexander Pope wrote of Newton: Nature and Natures laws lay hid in night; God said, Let Newton be! and all was light. In terms of astronomy, Newton gave reasons for and corrections to Keplers Laws. Kepler had proposed three Laws of Planetary motion based on Tycho Brahes data. These Laws were supposed to apply only to the motions of the planets. Further, they were purely empirical, that is, they worked, but no one knew why they worked. Newton changed all of that. First, he demonstrated that the motion of objects on the Earth could be described by three new Laws of motion, and then he went on to show that Keplers three Laws of Planetary Motion were but special cases of Newtons three Laws when his gravitational force was postulated to exist between all masses in the Universe. In fact, Newton showed that Keplers Laws of planetary motion were only approximately correct, and supplied the quantitative corrections that with careful observations proved to be valid. | text | null |
L_0328 | the history of astronom | T_1765 | The Big Bang Theory is the dominant and highly supported theory of the origin of the universe. It states that the universe began from an initial point which has expanded over billions of years to form the universe as we now know it. In 1922, Alexander Friedman found that the solutions to Einsteins general relativity equations resulted in an expanding universe. Einstein, at that time, believed in a static, eternal universe so he added a constant to his equations to eliminate the expansion. Einstein would later call this the biggest blunder of his life. In 1924, Edwin Hubble was able to measure the distance to observed celestial objects that were thought to be nebula and discovered that they were so far away they were not actually part of the Milky Way (the galaxy containing our sun). He discovered that the Milky Way was only one of many galaxies. In 1927, Georges Lemaitre, a physicist, suggested that the universe must be expanding. Lemaitres theory was supported by Hubble in 1929 when he found that the galaxies most distant from us also had the greatest red shift (were moving away from us with the greatest speed). The idea that the most distance galaxies were moving away from us at the greatest speed was exactly what was predicted by Lemaitre. In 1931, Lemaitre went further with his predictions and by extrapolating backwards, found that the matter of the universe would reach an infinite density and temperature at a finite time in the past (around 15 billion years). This meant that the universe must have begun as a small, extremely dense point of matter. At the time, the only other theory that competed with Lemaitres theory was the Steady State Theory of Fred Hoyle. The steady state theory predicted that new matter was created which made it appear that the universe was expanding but that the universe was constant. It was Hoyle who coined the term Big Bang Theory which he used as a derisive name for Lemaitres theory. George Gamow (1904 - 1968) was the major advocate of the Big Bang theory. He predicted that cosmic microwave background radiation should exist throughout the universe as a remnant of the Big Bang. As atoms formed from sub-atomic particles shortly after the Big Bang, electromagnetic radiation would be emitted and this radiation would still be observable today. Gamow predicted that the expansion of the universe would cool the original radiation so that now the radiation would be in the microwave range. The debate continued until 1965 when two Bell Telephone scientists stumbled upon the microwave radiation with their radio telescope. | text | null |
L_0329 | thermosphere and beyond | T_1766 | The density of molecules is so low in the thermosphere that one gas molecule can go about 1 km before it collides with another molecule. Since so little energy is transferred, the air feels very cold (See opening image). | text | null |
L_0329 | thermosphere and beyond | T_1767 | Within the thermosphere is the ionosphere. The ionosphere gets its name from the solar radiation that ionizes gas molecules to create a positively charged ion and one or more negatively charged electrons. The freed electrons travel within the ionosphere as electric currents. Because of the free ions, the ionosphere has many interesting characteristics. At night, radio waves bounce off the ionosphere and back to Earth. This is why you can often pick up an AM radio station far from its source at night. | text | null |
L_0329 | thermosphere and beyond | T_1768 | The Van Allen radiation belts are two doughnut-shaped zones of highly charged particles that are located very high the atmosphere in the magnetosphere. The particles originate in solar flares and fly to Earth on the solar wind. Once trapped by Earths magnetic field, they follow along the fields magnetic lines of force. These lines extend from above the Equator to the North Pole and also to the South Pole, then return to the Equator. | text | null |
L_0329 | thermosphere and beyond | T_1769 | When massive solar storms cause the Van Allen belts to become overloaded with particles, the result is the most spectacular feature of the ionosphere the nighttime aurora (Figure 1.1). The particles spiral along magnetic field lines toward the poles. The charged particles energize oxygen and nitrogen gas molecules, causing them to light up. Each gas emits a particular color of light. (a) Spectacular light displays are visible as the aurora borealis or northern lights in the Northern Hemisphere. (b) The aurora australis or southern lights encircles Antarctica. What would Earths magnetic field look like if it were painted in colors? It would look like the aurora! This QUEST video looks at the aurora, which provides clues about the solar wind, Earths magnetic field and Earths atmosphere. Click image to the left or use the URL below. URL: | text | null |
L_0329 | thermosphere and beyond | T_1770 | There is no real outer limit to the exosphere, the outermost layer of the atmosphere; the gas molecules finally become so scarce that at some point there are no more. Beyond the atmosphere is the solar wind. The solar wind is made of high-speed particles, mostly protons and electrons, traveling rapidly outward from the Sun. | text | null |
L_0331 | tides | T_1779 | Tides are the daily rise and fall of sea level at any given place. The pull of the Moons gravity on Earth is the primary cause of tides and the pull of the Suns gravity on Earth is the secondary cause (Figure 1.1). The Moon has a greater effect because, although it is much smaller than the Sun, it is much closer. The Moons pull is about twice that of the Suns. To understand the tides it is easiest to start with the effect of the Moon on Earth. As the Moon revolves around our planet, its gravity pulls Earth toward it. The lithosphere is unable to move much, but the water is pulled by the gravity and a bulge is created. This bulge is the high tide beneath the Moon. On the other side of the Earth, a high tide is produced where the Moons pull is weakest. These two water bulges on opposite sides of the Earth aligned with the Moon are the high tides. The places directly in between the high tides are low tides. As the Earth rotates beneath the Moon, a single spot will experience two high tides and two low tides approximately every day. High tides occur about every 12 hours and 25 minutes. The reason is that the Moon takes 24 hours and 50 minutes to rotate once around the Earth, so the Moon is over the same location every 24 hours and 50 minutes. Since high tides occur twice a day, one arrives each 12 hours and 25 minutes. What is the time between a high tide and the next low tide? The gravity of the Sun also pulls Earths water towards it and causes its own tides. Because the Sun is so far away, its pull is smaller than the Moons. Some coastal areas do not follow this pattern at all. These coastal areas may have one high and one low tide per day or a different amount of time between two high tides. These differences are often because of local conditions, such as the shape of the coastline that the tide is entering. The gravitational attraction of the Moon to ocean water creates the high and low tides. | text | null |
L_0331 | tides | T_1780 | The tidal range is the difference between the ocean level at high tide and the ocean level at low tide (Figure 1.2). The tidal range in a location depends on a number of factors, including the slope of the seafloor. Water appears to move a greater distance on a gentle slope than on a steep slope. | text | null |
L_0331 | tides | T_1781 | If you look at the diagram of high and low tides on a circular Earth above, youll see that tides are waves. So when the Sun and Moon are aligned, what do you expect the tides to look like? Waves are additive, so when the gravitational pull of both bodies is in the same direction, the high tides are higher and the low tides lower than at other times through the month (Figure 1.3). These more extreme tides, with a greater tidal range, are called spring tides. Spring tides dont just occur in the spring; they occur whenever the Moon is in a new-moon or full-moon phase, about every 14 days. Neap tides are tides that have the smallest tidal range, and they occur when the Earth, the Moon, and the Sun form a 90o angle (Figure 1.4). They occur exactly halfway between the spring tides, when the Moon is at first or last quarter. How do the tides add up to create neap tides? The Moons high tide occurs in the same place as the Suns low tide and the Moons low tide in the same place as the Suns high tide. At neap tides, the tidal range is relatively small. The tidal range is the difference between the ocean level at high tide and low tide. Studying ocean tides rhythmic movements helps scientists understand the ocean and the Sun/Moon/Earth system. This QUEST video explains how tides work, and visits the oldest continually operating tidal gauge in the Western Hemisphere. Click image to the left or use the URL below. URL: | text | null |
L_0331 | tides | T_1781 | If you look at the diagram of high and low tides on a circular Earth above, youll see that tides are waves. So when the Sun and Moon are aligned, what do you expect the tides to look like? Waves are additive, so when the gravitational pull of both bodies is in the same direction, the high tides are higher and the low tides lower than at other times through the month (Figure 1.3). These more extreme tides, with a greater tidal range, are called spring tides. Spring tides dont just occur in the spring; they occur whenever the Moon is in a new-moon or full-moon phase, about every 14 days. Neap tides are tides that have the smallest tidal range, and they occur when the Earth, the Moon, and the Sun form a 90o angle (Figure 1.4). They occur exactly halfway between the spring tides, when the Moon is at first or last quarter. How do the tides add up to create neap tides? The Moons high tide occurs in the same place as the Suns low tide and the Moons low tide in the same place as the Suns high tide. At neap tides, the tidal range is relatively small. The tidal range is the difference between the ocean level at high tide and low tide. Studying ocean tides rhythmic movements helps scientists understand the ocean and the Sun/Moon/Earth system. This QUEST video explains how tides work, and visits the oldest continually operating tidal gauge in the Western Hemisphere. Click image to the left or use the URL below. URL: | text | null |
L_0331 | tides | T_1781 | If you look at the diagram of high and low tides on a circular Earth above, youll see that tides are waves. So when the Sun and Moon are aligned, what do you expect the tides to look like? Waves are additive, so when the gravitational pull of both bodies is in the same direction, the high tides are higher and the low tides lower than at other times through the month (Figure 1.3). These more extreme tides, with a greater tidal range, are called spring tides. Spring tides dont just occur in the spring; they occur whenever the Moon is in a new-moon or full-moon phase, about every 14 days. Neap tides are tides that have the smallest tidal range, and they occur when the Earth, the Moon, and the Sun form a 90o angle (Figure 1.4). They occur exactly halfway between the spring tides, when the Moon is at first or last quarter. How do the tides add up to create neap tides? The Moons high tide occurs in the same place as the Suns low tide and the Moons low tide in the same place as the Suns high tide. At neap tides, the tidal range is relatively small. The tidal range is the difference between the ocean level at high tide and low tide. Studying ocean tides rhythmic movements helps scientists understand the ocean and the Sun/Moon/Earth system. This QUEST video explains how tides work, and visits the oldest continually operating tidal gauge in the Western Hemisphere. Click image to the left or use the URL below. URL: | text | null |
L_0334 | tree rings ice cores and varves | T_1789 | In locations where summers are warm and winters are cool, trees have a distinctive growth pattern. Tree trunks display alternating bands of light-colored, low density summer growth and dark, high density winter growth. Each light-dark band represents one year. By counting tree rings it is possible to find the number of years the tree lived (Figure 1.1). The width of these growth rings varies with the conditions present that year. A summer drought may make the tree grow more slowly than normal and so its light band will be relatively small. These tree-ring variations appear in all trees in a region. The same distinctive pattern can be found in all the trees in an area for the same time period. Scientists have created continuous records of tree rings going back over the past 2,000 years. Wood fragments from old buildings and ancient ruins can be age dated by matching up the pattern of tree rings in the wood fragment in Cross-section showing growth rings. question and the scale created by scientists. The outermost ring indicates when the tree stopped growing; that is, when it died. The tree-ring record is extremely useful for finding the age of ancient structures. | text | null |
L_0334 | tree rings ice cores and varves | T_1790 | Besides tree rings, other processes create distinct yearly layers that can be used for dating. On a glacier, snow falls in winter but in summer dust accumulates. This leads to a snow-dust annual pattern that goes down into the ice (Figure gather allows them to determine how the environment has changed as the glacier has stayed in its position. Analyses of the ice tell how concentrations of atmospheric gases changed, which can yield clues about climate. The longest cores allow scientists to create a record of polar climate stretching back hundreds of thousands of years. | text | null |
L_0334 | tree rings ice cores and varves | T_1791 | Lake sediments, especially in lakes that are located at the end of glaciers, also have an annual pattern. In the summer, the glacier melts rapidly, producing a thick deposit of sediment. These alternate with thin, clay-rich layers deposited in the winter. The resulting layers, called varves, give scientists clues about past climate conditions (Figure 1.3). A warm summer might result in a very thick sediment layer while a cooler summer might yield a thinner layer. | text | null |
L_0335 | troposphere | T_1792 | The temperature of the troposphere is highest near the surface of the Earth and decreases with altitude. On average, the temperature gradient of the troposphere is 6.5o C per 1,000 m (3.6o F per 1,000 ft) of altitude. Earths surface is the source of heat for the troposphere. Rock, soil, and water on Earth absorb the Suns light and radiate it back into the atmosphere as heat, so there is more heat near the surface. The temperature is also higher near the surface because gravity pulls in more gases. The greater density of gases causes the temperature to rise. Notice that in the troposphere warmer air is beneath cooler air. This condition is unstable since warm air is less dense than cool air. The warm air near the surface rises and cool air higher in the troposphere sinks, so air in the troposphere does a lot of mixing. This mixing causes the temperature gradient to vary with time and place. The rising and sinking of air in the troposphere means that all of the planets weather takes place in the troposphere. | text | null |
L_0335 | troposphere | T_1793 | Sometimes there is a temperature inversion, in which air temperature in the troposphere increases with altitude and warm air sits over cold air. Inversions are very stable and may last for several days or even weeks. Inversions form: Over land at night or in winter when the ground is cold. The cold ground cools the air that sits above it, making this low layer of air denser than the air above it. Near the coast, where cold seawater cools the air above it. When that denser air moves inland, it slides beneath the warmer air over the land. Since temperature inversions are stable, they often trap pollutants and produce unhealthy air conditions in cities (Figure 1.1). Smoke makes a temperature inversion visible. The smoke is trapped in cold dense air that lies beneath a cap of warmer air. At the top of the troposphere is a thin layer in which the temperature does not change with height. This means that the cooler, denser air of the troposphere is trapped beneath the warmer, less dense air of the stratosphere. Air from the troposphere and stratosphere rarely mix. Click image to the left or use the URL below. URL: | text | null |
L_0336 | tsunami | T_1794 | Tsunami are deadly ocean waves from the sharp jolt of an undersea earthquake. Less frequently, these waves can be generated by other shocks to the sea, like a meteorite impact. Fortunately, few undersea earthquakes, and even fewer meteorite impacts, generate tsunami. | text | null |
L_0336 | tsunami | T_1795 | Tsunami waves have small wave heights relative to their long wavelengths, so they are usually unnoticed at sea. When traveling up a slope onto a shoreline, the wave is pushed upward. As with wind waves, the speed of the bottom of the wave is slowed by friction. This causes the wavelength to decrease and the wave to become unstable. These factors can create an enormous and deadly wave. Landslides, meteorite impacts, or any other jolt to ocean water may form a tsunami. Tsunami can travel at speeds of 800 kilometers per hour (500 miles per hour). | text | null |
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