Where in the solar system is the most viable place to put my colonists, after Mars and Luna?

Question: Mars and Earth's moon already feature in a lot of fiction about space colonization. After these two planets, and assuming that other solar systems are too far away, what is the best place within this solar system to colonize?
Comment: It seems to me, that after the Moon, the next best option is to create artificial satellites and space stations. I don't see any of the other planets (including Mars) as being viable options unless there is some giagantic leap forward in spacecraft. There would be long periods of time when the Sun is between the earth and the other planet.
Comment: By far the most viable place for colonisation within our solar system is **Earth**.
Comment: [Here is an interesting article](http://www.citylab.com/tech/2014/07/the-surprisingly-strong-case-for-colonizing-venus/373560/) about colonising Venus.
Comment: While I think we can get there, my concern is that Mars and Earth are cut off from each other for certain stretches of time. It would make sense, that going to Mars will work best AFTER Earth has "passed" Mars in orbit and vice versa. These windows would be available around every 26 months. That is a long time to leave people alone on the red planet. Which isn't to say it isn't worth starting. But colonizing the planet I would think needs technology to quickly move between planets no matter where they are.
Comment: @JamesRyan No, the sun is not large enough to go nova. According to our current understanding, though, it's going to turn into a red giant in somewhere around 5e9 years, and might well grow in size perhaps enough to engulf Earth's (current) orbit. But no place is perfect.
Comment: @Pink You've obviously not read about Mars Direct. (http://en.wikipedia.org/wiki/Mars_Direct) We don't need *that* large of a leap- more of a normal-sized step, really.
Comment: What, no love for **THE** spacefaring sci-fi series? The _Space Odyssey_ series has humans colonizing Ganymede and Callisto, with an aquatic species evolving on Europa with the Monolith's help.
Comment: In English, it's called "the Moon".  (Likewise, that star we orbit is "the Sun".)
Comment: but Earth is already ''colonized'' by mankind
Comment: The best place for colonisation would be outside our solar system because the sun is going to blow up.
Comment: At the risk of being cheeky, but totally honest, I would propose next colonizing a place we have not colonized in our solar system: Underwater on Earth.  Would it be downvoted, if I explained why, since there is a 'space' tag?
Comment: @Mikey thinking out-of-the-box is a good thing, IMO. Why not Antartica, then?
Comment: @Mikey that being said… developing a colony outside of Earth is something that will help us in a distant future should the Earth itself have… "problems". And this isn't solved by colonizing a new place on the Earth itself.
Comment: @Lohoris agreed, but we will have already two well-established colonies (Mars & Luna).
Comment: See also [this later question](http://worldbuilding.stackexchange.com/questions/56243/order-of-solar-system-colonization)
Answer: The Asteroid belt.

It has similar requirements for life-support systems as the moon. With the additional need perhaps for some areas with simulated gravity.
It is next closest in terms of energy required to get to and from the orbits.
It is still close enough to the sun that collecting solar energy is workable (the farthest out we have used solar panels is Jupiter - on the Juno mission).
The cost of landing and launching from an asteroid are reduced thanks to the low gravity. This makes them attractive as way stations to inner and outer locations, as well as making it easier to deliver supplies or to collect produce.
It is thought that some asteroids will be worth mining for rare elements.
Yet other asteroids contain water ice or other volatile compounds, potentially useful fuel or raw materials for production or organic feedstock.
Collisions are much rarer than you might believe from science-fiction staple of spaceships dodging rocks in a dogfight. Typically you would only see one asteroid at a time, maybe a few others could be seen as sunlight-reflecting dots many thousands of kilometres away.
Comment: Additionally, there are ice asteroids, which can provide a source of water.
Comment: @Zxyrra: Comments are not a place to debate this properly - perhaps ask a separate question. It will depend on purpose, but the cost is much less to change between different asteroid orbits than to go between other more distant orbits. Like order-of-magnitude different. If you include the gravitational well for other starting locations (such as Earth or Moon), you can probably multiply in another order of of magnitude or two. Costs of space travel are highly variable and location is super important.
Comment: You might even be able to propel the smaller asteroids and fly like a spaceship as happened in the 1950s radio serial Journey into Space http://en.wikipedia.org/wiki/Journey_into_Space#The_World_in_Peril
Comment: I'd also think the asteroid belt would be the initial startings of a Dyson sphere (ring?) setup.
Comment: Additionally, because work(Watt) depends on gravity and asteroids barely have any gravity you'd get much more work done out of sources of energy not generated on the asteroid. Ie: If a crane lift up a 100 kg rock on earth it must have enough energy to lift up 980 newtons worth of mass. On an asteroid the same rock would be worth 11 newton so you could lift 89 asteroid stones for the same price as 1 on Earth.
Comment: However, unlike popular fiction portrayals, it's extremely sparsely populated - so it has no real value over parking in empty stellar space unless you have the energy to track down lonely asteroids.
Comment: @Zxyrra: The difference between parking a spaceship and using an asteroid as a base is going to be significant because of access to raw materials. The cost of sending millions of tons of metals to a solar orbit higher than Earth's is very high. If they are already there, and you have a use for them (additional habitat, or constructing larger vessels that will remain in high orbit), then the cost benefit is also high.
Comment: @NeilSlater But those resources may not be worth it. I'm just thinking that traveling thousands of miles to reach each small, isolated pocket of barren rock is less cost effective that staying stationary on or near an actual planet, where you may need less fuel to get to more material that isn't rapidly propelled through space relative to your ship.
Comment: @NeilSlater If the cost of sending material into orbit once is high, surely the cost of sending it to the asteroid belt and changing direction constantly, while mining at every location, is higher.
Answer: My choices: Ganymede and Callisto (and maybe Titan)
This is perhaps a bit of a buzzkill, but I honestly would not recommend colonizing much in the solar system besides the Moon and Mars. Here's why I would take a lot of bodies off the table:

Mercury - Too hot on its sunny side for colonization (up to 700K) and too cold on its dark side (down to 100K). Solar power on its sunny side would be tricky as parts of the solar array could melt. Also not too special resources-wise.
Venus - Generally a hellish place to be. High atmospheric pressure means spacecraft can (and have been) completely crushed. A runaway greenhouse effect means temperatures are extremely high (737 K), and clouds of sulfuric acid make rainy days pretty bad.
Asteroid Belt - A lot of small bodies. Hard to track smaller asteroids because of the concentration. Not a lot of collisions, but there's always the possibility. Low-gravity means that you won't have a substitute for terra firma anywhere.
Jupiter - obviously not a good place to land a spacecraft. Fairly far away, which means that "Houston, we have [had] a problem" will go unheard for a couple minutes. The one thing in its favor is that many of its moons are fairly large. From here on out, solar power becomes less feasible.
Saturn - Same issues as Jupiter. This would actually be, in my opinion, the best of the bunch, because you could find raw materials in its rings. It, too, has a lot of moons, but they really aren't big enough to support a proper colony.
Uranus - same issues as Jupiter. Also, we the voyage here would take a long time.
Neptune - same issues as Uranus.
Beyond - You have the Kuiper Belt and the Oort Cloud as you get beyond Neptune. There are lot of small, rocky and icy bodies here, such as comets, and a few dwarf planets. Again, travel time and communication time are issues, and there's not a lot of gravity to make a large-scale colony. You could get some water here, but it would be in the form of ice. There could also be minerals, but, once again, it's pretty far away. Its cousin, the asteroid belt, is a better option.

Here's why the Moon and Mars are much better targets:

The Moon - Very close to home. Easy to get to and easy to send messages to. We've already been there, and have proven we can land there and even drive around.
Mars - Not too far away. We've sent a lot of landers there. Good gravity, so it would be easy to adapt to. Terraforming is also an option.

The Moons
You can thank durron597 and cHao for this little section. I did not address the moons of the solar system in my answer - in fact, I may have unfairly written them off - and so I'll add a little bit about them here.

Moons of Mars - Mars has two moons, Deimos and Phobos. They're fairly small, and are most likely former asteroids. I hope we can all agree that they're not fantastic targets for colonization - in fact, Phobos is expected to enter Mars' Roche limit at some time in the far future, and be broken into a small ring. This of course doesn't stop near-term colonization. Their size is an issue, though.
Moons of Jupiter - Jupiter has at least 67 moons, the most of any planet in the solar system. The biggest four are the Galilean moons - Io, Europa, Ganymede, and Callisto. They rival (or surpass) Mercury in size. Europa is famous for its icy oceans, and has been considered (by others in this question) as a good place to colonize. I would put that destination on hold until we know more about it, but it has merit. Io has many volcanoes, which could prove detrimental to any intrepid Jovian lunar explorers. Ganymede is larger than Mercury (good) but is much less massive (bad). This might be the most promising of all the Jovian moons, especially since it has a thin atmosphere of oxygen. It also has a magnetosphere. It would be one of my two picks to colonize. That said, Callisto also has some promise. It has a thin atmosphere and is about the size of Mercury - though much less massive. It has also been well-explored, and has water on the form of ice. Therefore, I would nominate it, alongside Ganymede, for a target of human colonization.
Moons of Saturn - Saturn has 62 moons, the most famous of which is Titan. Like Ganymede and Callisto, it is about the size of Mercury, but, like them, is much less massive. It has hydrocarbon lakes and a nitrogen atmosphere. It does have some water ice but also rains of methane. It could supported life in the past (or could now), but any such creatures would have different metabolisms than us, and be based on different chemicals. I wouldn't rule out Titan as a target, but its methane lakes worry me a little. The nitrogen atmosphere is really good, though. Saturn's other moons are less prominent, although not to be ignored. The ring system could also be a decent target. I'd rank Titan as my third choice, after Ganymede and Callisto.
Moons of Uranus - Uranus has a measly 27 moons, most of which are named after Shakespearean characters. Most are much smaller than Earth's moon. Many may have water in the form of ice buried inside them. The downside to colonizing Uranian moons is the travel time - it would take years to get to Uranus. But again, the ring system could provide some good materials.
Moons of Neptune - Neptune's 14 moons are, like Neptune, fairly far away. Once again, we have the travel/communication problem. Triton, the largest, most likely has a lot of water - again, in the form of ice. It also has nitrogen, although its atmosphere is much less dense than Earth.
Comment: @HDE226868: On the other hand, methane is also a possible fuel source, if you can scrounge up some oxygen somewhere.
Comment: @Lohoris My objection to Europa was that we really don't know what's below the ice.
Comment: Underground facilities might be possible for the moon of Jupiter, but the radiation from the planet's magnetic field is lethal on the surface. It's been compared to standing in a nuclear reactor.
Comment: @ValekHalfHeart, more precisely: like standing in very large cyclotron. Gives Cancerman superpower in no time.
Comment: Phobos is closer to Mars's surface in delta-V terms, which, again, is the only thing making it particularly interesting. Think of it as the shipping terminal for the Mars colony.
Comment: @durron597 You can expect an update later. But the methane on Titan seems like it could be detrimental to colonization, and Europa is relatively unexplored. But I'll update it later, when I have time.
Comment: @cHao Good point. I'll have a lot or work to do later. (Sigh).
Comment: @durron597 I changed a little.
Comment: @cHao I changed a little.
Comment: @HDE226868 I don't agree with your writeoff of Europa (obviously) but I can see why you disagree; +1 for effort/completeness.
Comment: @durron597 Same reason I gave you +1 for Europa. I haven't completely put Europa off, but there's just so much we don't know about it - yet.
Comment: I don't understand why you rule out Europa but include Ganymede and Callisto. Do you claim that we don't know enough about Europa, _but_ we _do_ know enough about the other two? If that's so, it's not clear. If it isn't so, no clue.
Comment: A lot more comprehensive now.  And i'm a sucker for good space pictures. :)  +1
Comment: @ValekHalfHeart sure, the radiation may be lethal, but on the flipside it may be a goldmine of mutant and/or superpowers.  It's worth the gamble.
Comment: @HDE226868, there is very few sulphuric acid in the Venus atmosphere. Real problem is gazillion tons of plain old carbon dioxide. Also, Mercury might be mineral resource rich.
Comment: Phobos is interesting as a staging area for Mars exploration or colonization, not so much as a destination of its own. It takes less delta-V to reach than the surface of the moon, and almost nothing to take off from into Mars orbit.
Comment: @RussellBorogove True, but the low surface gravity means that any maneuvering before a landing would be tricky, and it wouldn't hold much promise except as a stopping point to Mars - and you still have to go down there, eventually.
Comment: I think 5mm/s^2 surface gravity means you're docking, not landing. The first landings would have to be done with active harpoon and hold-down thrusters, like Philae, then you dig out a docking bay...
Comment: @RussellBorogove Is there really anything on Phobos that's of much interest, though? The point of colonization is to have a destination; if Mars is the target, you're probably better off just going down there in the first place. I *can* see Phobos being an interesting secondary target, though. Out of curiosity, why didn't you mention Deimos?
Comment: +1 For the Roche Limit link!!! Did not know about that, super interesting read!!!!
Answer: Venus but not the surface.  In some ways Venus is much better than Mars for a colonization target.  It has better gravity for humans (.9G vs .38G for Mars). It is closer than Mars(40 million Km vs 55 million Km). At 50 km above the surface the temp is 0-50 C and the atmospheric pressure is the same as Earth's(no need for pressurized suits, no explosive decompression). The atmosphere is largely made of carbon dioxide so it would be possible to produce oxygen. Being closer to the sun means solar power would be quite usable. The biggest draw back would be the clouds made of sulfuric acid.
Incidentally this Wikipedia page covers pretty much every where in the solar system we might try to colonize.
Comment: Came here to give venus some love, nice to see someone already beat me to it. Venus is a *better* destination than Mars
Comment: It gets even easier if you push some metal rich asteroids into orbit - these will probably be easier to extract solid materials from than the surface of the planet!

That being said, I'm all for Venus, too. It's not BETTER than Mars because of how difficult it would be to extract materials for use, but it's at least going to protect you from stellar radiation better than many of the moons on offer here.
Answer: Europa
http://en.wikipedia.org/wiki/Europa_(moon)
Pros:

Lots of water, and all the advantages that brings

Narrow range of temperature (even though it's still -171 °C)
Relatively easy power source (fusion, assuming we have effective fusion by the time we're colonizing Europa)
Raw materials we can use to build things like hydroponics bays

Lots of oxygen in the atmosphere
Gravity only slightly less than Luna
Close to Jupiter, for when we start mining Jupiter's atmosphere for fuel

Cons:

Really really cold
Low gravity still a problem, but by the time we're colonizing Europa, we should have solved this problem on Luna.
Jupiter's radiation (thanks Michael Kjörling in the comments)
Comment: Jupiter's radiation also poses a potentially serious problem, though I don't know exactly how serious. It should absolutely go on the "cons" side, though.
Comment: If we have fusion, we could use it anywhere. Good for you for showing the cons of your idea, though. +1.
Comment: @HDE226868 You still need to bring the fuel with you to places like Luna or Mercury. That's the advantage of Europa
Comment: @HDE226868 2H2O -> 2H2 + O2 is a very well studied process. And once you have the hydrogen, you can (relatively) easily refine out Deuterium and Tritium. This is a lot easier than, say, extracting hydrocarbons from rock or locating a fissionable material.
Comment: Lots is a stretch - it's low pressure. It's still a good source of oxygen though, nice spot.
Comment: @durron597 Because there's enough refined nuclear fuel on Europa waiting to be accessed? I doubt it would be easy to use.
Comment: @durron597 Well-studied, yes. But not easy, by any standards.
Comment: @HDE226868 I strongly doubt we are going to be making colonies beyond Luna and Mars without figuring out how to capitalize on fusion power. Bringing fuel with you is just too expensive.
Comment: @durron597 True, I hadn't considered that.
Comment: Let's not forget the race of sentient robots inhabiting it.   (reference to a certain movie :P )
Comment: @MichaelKjörling A very serious problem indeed. Jupiter's radiation belts are a million times stronger than the Van Allen belts around Earth, which are already hazardous to astronauts. (http://www.astrobio.net/news-exclusive/hiding-from-jupiters-radiation/) And they encompass all the major moons. Ganymede does have a weak magnetic field that provides some protection, but I don't know how close it is to sufficient.
Comment: @MarkFoskey Callisto is outside of Jupiter's radiation belts and receives very low amounts of radiation.
Answer: Why so little love for Ganymede?
I feel that if we had already colonized the Moon due to proximity, Mars due to being close and similar enough (and heavily studied), we'd probably be ready to take on other worlds. However, picking a planet like Venus seems like what you'd do in game for challenge (see Eve) - Venus is hell; it's hot, it's thick and probably has raging storms all the time. It would be dangerous to try to poke through the atmosphere. Mercury on the other hand is way too close to the Sun - while it has a strong magnetic field, getting to it would require a lot of fuel. It just doesn't seem cost-effective to try colonizing these two, not even for scientific research which can be done through probes.
Jupiter's moons however are a lot calmer. While they may have issues with heat cycles, day-night cycles and radiation, if we've colonized the Moon and Mars, we'd already have solved these issues - the radiation on the either would be too high for humans and we'd need some very effective systems to prevent problems. The Moon is also tidally locked, so we'd have solved this already.
Jupiter's moons have the advantage of being both closer than the other gas giants and being part of a system that resembles the inner solar system's terrestrial planet group. As you can tell, I've got my eye on Ganymede. Here's why it's awesome:

Has a differentiated inner structure, so we get a magnetic field (it's the only moon known to have one, so if Mercury is out, this is the best place to go to find one)
Seems to have oceans, which is great for terraforming
Isn't too far or too close to Jupiter (it'll feel like home, with Io and Europa oribiting closer and Callisto behind it).
Has no atmosphere, but we've already dealt with that on the Moon, right?

Callisto is too barren and cold and Europa is little more than an ice moon. If I was asked, I'd recommend Ganymede.
Comment: Jupiter's radiation belts are far more severe than anywhere else in the solar system. The Juno space probe has a thick aluminum box to protect its electronics, and it's only in the belts for a small fraction of its orbit. And it's not human. I'm pretty sure no spacecraft could get humans to the moons before they would get a serious, maybe fatal, dose of radiation - shielding would be mass prohibitive.
Comment: Callisto is outside those radiation belts of Jupiter and so would be more suitable in that regard.  Still likely has oceans, though an undifferentiated core.  Add as much atmosphere as humans can handle, say 3 to 4 atm pressure, including chloroflorocarbons for a strong greenhouse effect and you might get closer to a colonizable body.  Which with it's lower gravity will take significantly more atmosphere to achieve.  Unfortunately if get you passed the freezing point of water on a regular basis you will melt the ground beneath you but the creative mind can find a way.  (House boat habitats?)
Answer: I'm not sure about after Mars and the Moon, but there's a place I'd take before them: Earth orbit. Low Earth orbit is pretty compelling: easy access to all existing human civilization, radiation protection, fairly easy access to space resources and a good launching point for other locations.
High Earth orbit or Lunar orbit are both also very good. They are preferable to the Moon's surface because we can make custom gravity and day lengths via rotation and shutters, taking off from them is a lot easier than a surface launch, there's more sunlight available, and they are just physically closer to Earth, where everybody is going to want to be coming and going for the near future, among other things.
I'd prefer orbit to a planet's surface even if space colonies were very well established and proximity/ease of access to Earth wasn't important anymore!
Read more about them here:
http://en.wikipedia.org/wiki/Space_habitat
http://space.mike-combs.com/spacsetl.htm
Comment: This is my choice for the same reasons, but you need to come up with the materials for your space colonies. Learning how to mine the asteroids will take some time, and we can't build a space elevator today. LEO has a nasty problem of atmospheric drag, its a bummer when your colony returns to Earth.
Answer: Mercury, but with a major and rather obvious caveat - not in the direct sunlight.
Possibly subsurface at the poles or within some of the deep craters that are always in shadow.  There would be almost limitless energy provided from the sun.  The extremely low axial tilt means that the areas of shade would remain relatively consistent during the Mercurian year.
Low gravity, very similar to the value for Mars (see link above) and no appreciable atmosphere making transport easier.
Would provide a very stable base for solar observation and power generation.
Comment: Borrowing liberally from [Wikipedia](https://en.wikipedia.org/wiki/Mercury_%28planet%29#Research_with_space_probes): "Mercury has an orbital speed of 48 km/s, whereas Earth's orbital speed is 30 km/s. Thus the spacecraft must make a large change in velocity (delta-v) to enter a Hohmann transfer orbit that passes near Mercury, as compared to the delta-v required for other planetary missions. ... requiring another large delta-v change to do anything other than rapidly pass by Mercury. ... A trip to Mercury requires more rocket fuel than that required to escape the Solar System completely."
Comment: That can be said for any of the propositions.
Comment: One problem I see, mercury is incredibly difficult to reach and get away from due to being so far into the gravity well of the sun.
Comment: True, however, by the time colonisation has reached that far, we would most likely have overcome those problems
Comment: Mercury has the advantage over Venus of being able to get away from the heat. Venus would need considerable engineering, perhaps terraforming, before the problem was surmountable there, whilst on Mercury without a dense atmosphere, just "stay in the shade" works very well.
Comment: @MichaelKjörling Such is the case with most landings and takeoffs. They use many times more fuel than coasting through space. It's apples and oranges.
Comment: That would need to be weighed up against the potential benefits of such a colony.
Comment: @fredsbend Indeed (and don't worry, I'm reasonably familiar with the theory behind space travel). However, escaping the solar system entirely means that you have to climb out of Sol's gravity well completely, which is non-trivial, so the comparison is reasonable. Delta-v is a real party-pooper in spaceflight.
Comment: @MichaelKjörling The only thing comparable is fuel usage. They differ on everything else. If you could take what you learn about landings and takeoffs and apply it to spaceflight, or vise versa, then we could say they are comparable. This would be like comparing the drag racer on the strip using x gallons of fuel to go a 1/4 mile and the pinto on the highway using that same x gallons volume to go 200 miles. They are performing completely different functions of transportation, thus, use fuel differently.
Comment: As others have said the Δv is painful, I don't think you're colonizing it until you have mass drivers in place that can throw the ships.  However, temperature-wise it actually works well.  There's a ring around the poles where a deeply buried base experiences room temperature all the time.
Comment: Once the $\delta$v problem is overcome, I truly believe the benefits would be worth it.
Answer: As many have suggested, the Asteroid Belt would be an ideal location for colonization and resource-collecting, but with so many asteroids, which one do you choose?  I nominate...
Ceres
Ceres is an incredibly ideal choice for colonization.  For an asteroid, it has an incredible abundance of water, possibly even oceanic water, and plenty of clay material for construction.  It's the largest object in the asteroid belt, so it'll have more natural gravity than any other asteroids (though stilly very little).  It's even relatively warm compared to other asteroids, so heating costs won't be as high.
There is of course the problem of being located in the asteroid belt, and the possiblity of asteroid collisions - though this is much rarer than media would have you believe.  Any colony on Ceres will have to account for this possibility, though realistically the risk of collision isn't significantly higher than anywhere else in the solar system.
Comment: the asteroid belt is still almost entirely empty space. There isn't any practical difference in risk of collisions than anywhere else in the solar system.
Comment: @pluckedkiwi I'll take your word for it.  Edited.
Comment: Anything on Ceres would take the full brunt of cosmic radiation and the very frequent solar flares and other bad effects from solar weather. Humans would need to live under the asteroid to be shielded, equipment would short because of radiation. Also the temperature on Ceres vary from -105oC to -40oC. That basically mean the best weather ever on Ceres would be like the worst siberian winter you can think of.
Answer: Habitability
For a cosmic body to be habitable by humans, it needs to have a few things (or substitutes for those things):

Oxygen
Water
Correct temperature
Food source

Some of those we can bring with us (like some food and some water) but we won't be able to send enough supply ships to sustain a colony. Ideally, there should be some there already.
Temperature is a little different. We can affect it, but it's not easy. The easiest thing to do would be to find a planet in the Goldilocks (habitable) zone, which, for Sol, looks like this:

It seems that no other planet is in Sol's habitable zone. However, since we can affect the temperature of a planet, we can use those on either side of the zone.
Candidate 1: Venus
Is not that great for colonizing at the moment. Its atmosphere is 96% CO2; the temperature at the surface is 735K; and the atmospheric pressure is 92 times Earth's. However, it could be made habitable.

Remove CO2.
This both reduces atmospheric pressure since there isn't so much gas in the atmosphere, and reduces temperature by removing greenhouse gas that keeps it hot. This is by far the biggest job: you want to remove CO2 until the atmospheric pressure is about 0.79atm.
Add oxygen.
This makes it livable for us, as well as adding some more cooling effect.

For added bonus, you could remove the sulfur dioxide clouds in the atmosphere, which would lower acid rain levels once you add water. Don't forget the water.
Candidate 2: Asteroid Belt
This could be viable. The optimum here would be to make lots of smaller colonies on separate asteroids and develop asteroid-hopping ships to share resources. The asteroids have:

Minerals
Water (mostly ice)
Reasonable temperatures

They do not have:

Atmospheres
Gravity
Oxygen

Your colonists would need to build airtight, pressurised, oxygenated domes to live in, and they might well want to add some kind of artificial gravity. Other than that, this is a good target.
Candidate 3: Europa
The Wikipedia summary image captures why Europa is a good target quite well:

Europa's trailing hemisphere in approximate natural color. The prominent crater in the lower right is Pwyll and the darker regions are areas where Europa's primarily water [and] ice surface has a higher mineral content. Imaged on 7 September 1996 by Galileo spacecraft.

From that we can straight away tell that Europa has:

Minerals
Water (partially ice)
Low (or no) atmosphere (implied by the impact crater - bodies with atmospheres are less likely to be struck)

This is already good. All your colonists need now is artificial gravity and a sealed oxygenated dome to live in. As others have said, it is still possible to collect Solar power on Europa.
Choice
Out of the three candidates, I pick this order:

Europa
Asteroid belt
Venus

Europa wins because it takes the least amount of effort to make habitable and has most of the resources we need there already. The asteroid belt is not far behind, given that it has quite a lot of resources, but it takes more effort to set up and there is a higher risk of collision. Venus is a lot of effort to get to a livable state, so I would only send colonists there after a lot of work.
Comment: "Remove CO2, Add oxygen." - there in no way to do so in billions of years. And you would need SO much energy for it. There is actually no way to do so, it is easier to change Earth's orbit or take a planet from Alpha Centauri system and move it to the Solar System than replace the Venus's atmosphere.
Comment: I would put Callisto ahead of Europa due to the huge radiation differences, 540 rems a day (according to Anixx) vs. 0.01 rems, Earth surface takes in about 24 rems a year!  Also easier to leave Jupiter orbit from Callisto than Europa and less likely to harbor extant life.
Comment: On Europa you get 540 rems daily, a deadly dose of radiation every day, lol.
Comment: @Anixx - *best place* with no tech level specified, therefore I can assume the necessary technologies.
Comment: @Anixx do you know how one would calculate the amount of energy required? I'm curious on the order of magnitude in a sci-fi scenario. Could a total-conversion reactor transmuting the mass of CO2 to energy then transmuting a bit of energy to oxygen work? What's the mass of CO2 on Venus? A quick calculation gives about 2.69*10^26 GJ for all the CO2 on Earth.
Comment: Domes have been mentioned, along with the high radiation (a problem almost anywhere).  I'd think a better approach to colonies would be to bury them.  Tunneling is easier in lower gravity, and underground colonies are shielded from radiation, micrometeroites, etc.  A large asteroid would really be a good place for a buried colony.
Answer: As already mentioned the Asteroid Belt is a solid choice.
The other obvious choice is the moons, rings and general orbits of the gas giants, you have huge amounts of raw materials and energy available and the option of both gravity wells and free fall for people and industry to take place in.
Answer: For a space colonization except the cases the planet is located in the midst of habitable zone, it is usually desirable the planet/planetoid had no atmosphere. Vacuum works as a perfect termo-insulator, thus allowing to colonize planets located too close or too far from the Sun.
As such, in Solar system we have

Mercury - having no atmosphere is perfectly suitable for colonization. Lots of solar energy, there is some water ice in the permanently shaded areas on the poles. Unfortunately it rotates which makes the poles the most suitable areas for colonization, although populating other areas is also possible (but one would need to import water and erect sun-shields built from light-reflecting material). A better case would be if Mercury were tidally-locked, then the most habitable zone would be along the terminator line rather than only the poles. Surface area of Mercury is 75 million sq. km (compared to 144 for Mars and 460 for Earth).
Venus - has thick atmosphere and high temperature, totally unsuitable for surface colonization. Floating habitats are possible though, but why?
Ceres - has no atmosphere and a lot of water, perfectly suitable for colonization. This is most likely the third destination after Luna and Mars. Surface area is 2.8 million sq km.

Jupiter's system:

Io, Europa, Ganimede - all have no atmosphere and a lot of water, but also deadly radiation due to Jupiter's radiation belt. Seem to be unsuitable for colonization.
Callisto. Has no atmosphere and no deadly radiation. Also has a lot of water. Good place for colonization after Ceres and Mercury. Surface area is 73 million sq km, just like that of Mercury.

Saturn's system:

Titan while the largest sattelite, has a thick atmosphere at very low temperature. Also the atmosphere (containing cyanides) is deadly poitionous to humans even in small concentrations. Seems to be unsuitable.
Tethys, Dione, Rhea, Iapetus. All seem quite OK for colonization, having no atmosphere. Combined area is around 18 million sq. km.

Uranus' system

Ariel, Umbriel, Titania, Oberon. All seem to be quite suitable. Combined area is 23.6 million sq. km.

Neptune's system

Triton. Suitable for colonization, quite large with area at 23 million sq. km.

Trans-neptunian objects

All Trans-Neptunian objects seem to be well suitable for colonization if enough energy is provided. This includes Pluto, Charon (22.6 million sq km combined), Eris (18 million sq km), Haumea, Makemake, Orcus, Quaoar, Sedna and some others.
Comment: I can expand on that... In space, the primary means by which temperature is lost is radiation (there is nothing to conduct the thermal energy, so convection and conduction are negligible). So heat loss is actually kept to a minimum while in vacuum. If you are in an atmosphere, and it is really cold, then the atmosphere will conduct heat away from your habitat, forcing you to work really hard to not freeze. Also, no atmosphere means less obstruction for solar power.
Comment: A good answer, I'd like to see more discussion on why you consider no atmosphere so desirable though.
Comment: @Tim B atmosphere is very diffucult to thermo-insulate from. It is either too hot (Venus) or too cold (Titan) which requires special cooling/heating equipment. On Venus even automatic probes hardly can work more than 30 minutes. Besides this, atmosphere (even tiny one) complicates landing and launching from the surface. This became a major problem on Mars, although on Mars atmosphere is more a positive factor than negative because the thicker atmosphere there the warmer the climate due to greenhouse effect. But this is only a unique exception due to its precise location.
Comment: @Anixx Part of the reason probes on Venus can't work for too long is that a) It is *too* hot, and b) High atmospheric pressure.
Comment: @HDE 226868 yes, exactly. But pressure alone (at least at the scale found on Venus) is not a problem if the temperature is suitable.
Comment: @Anixx My point is that it's not just atmosphere that's a problem. Also, clouds of sulfuric acid can really ruin  lander's day.
Comment: @HDE 226868 and that is due to atmosphere. If Venus had not any, it would be a much nicer place.
Comment: @Anixx Yes, but. . . Okay, I can't really argue against that. I disagree that no atmosphere is desirable, but I can't argue against your logic.
Comment: @HDE 226868 any atmosphere on Venus would be ungood, no matter how thin.
Comment: @Anixx Why? By the way, move this to chat?
Comment: Yeah, it's an interesting discussion but too long for comments (ideally the responses would be incorporated into the answer and the comments removed). I suggest taking it to the general worldbuilding chat: http://chat.stackexchange.com/rooms/17213/worldbuilders-general-chat
Comment: Uranus has a very large area
Comment: ISS and other airless colonies would require a radiator system to expel the excess heat via radiation. In fact Mars may have too thin an atmosphere for convection to remove the heat from a colony and also require radiators, according to NASA. Also any extensive use of an airless body will quickly add some atmosphere to the body, though still very small. I agree an extensive atmosphere would cause heating problems on a cold body, it seems a middle ground of atmosphere may provide a minimal need for radiators or heating. Or pressure suits if above Armstrong limit and reduced structure strength.
Answer: If you have a viable technological basis to move around and survive long term in space, the true answer is anywhere you can extract water and collect energy. In principle you can do this virtually everywhere in the Solar System, so long as you arrange a "pipeline" of regular transports to deliver any missing ingredients to your chosen location (water ice to Mercury, for example), but I suspect you are looking for the best and most self contained location, where imports and exports would be at a minimum.
The best place would be the Jovian system. With the 4 large Galilean moons and 60+ smaller bodies orbiting Jupiter, you have plenty of open space to settle. This is actually very important, as I will explain later.
There are vast resources of water and minerals, but most importantly, there is a huge amount of energy available locally from the vast magnetosphere surrounding Jupiter. As Io passes through the magnetosphere, it acts as the armature of a generator,creating a huge "flux tube" running from Io to Jupiter and back, channeling millions of amps of electrical current. Man made satellites or electrodynamic tethers can be placed in orbit around Jupiter to do the same thing, but with much more control of the current, which can then be tapped and beamed via microwave or laser to anywhere in the system. Jovian colonists will have access to as much energy as they want to support their industry and lifestyles, a thriving space transportation system (spaceships using external "beam power" can be smaller and cheaper than self contained spacecraft) and whatever else they desire.
Having an open frontier is also important. People may settle in cities burrowed under the ice of the Galilean moons for protection from radiation and to mine the ice, but without an outlet, their civilization may eventually stagnate. IF young and adventurous people have an easily accessible opportunity to pack up and strike out on their own to inexpensive "land" and start anew then there is always a positive outlet for their energy and yearnings. People might also want to experiment with other social, religious or economic systems without interference, and this is an ideal setup for them to do so and share their findings without imposing on everyone else. Failed experiments can also be easily recovered, since the main settlements are relatively close in astronomical terms. The end result is the Jovian civilization will be much more vibrant and outward looking than virtually any other part of the Solar System, and the Jovians may eventually emerge as the political, economic and social leaders of the Solar System.
The other gas giant planets may have many similar attributes, but are not easily self contained with a rich energy source like Jupiter. Their colonists may be able to mine the atmospheres of their gas giant planets for 3He and use fusion energy for power, but this will be a more difficult and expensive option than the Jovians enjoy.
Answer: Earth orbit and Lagrange points.
We start with the Moon because it is a convenient source of raw materials which can be exported to build orbital habitats. The moon has no atmosphere, so you can launch stuff using a linear motor mass driver. No big rockets needed.It's also easy to obtain shelter against solar storms and meteorites by going underground. And it is close enough to Earth that self-sufficiency in small light hi-tech items can be postponed (indefinitely?) and emergency evacuation would be possible (mass-driver, one way "lifeboat" capsule).
Mars? I doubt it is worth the effort. That thin unbreathable atmosphere is an utter pain to get in to and out of.. Vacuum is easier.
Some exploration of the Asteroid belt is likely. It may prove to be a better source of some elements than accessible Lunar rock. If this is the case then there may be semi-permanent settlemens on asteroids, like mining towns on Earth.
You need to think big if it is ever going to happen. Shielding against Solar storms requires walls several feet thick. Substituting gravity by rotation likewise implies large. Build habitats a lot like John Varley's titans, but without the insane goddess.
The goal? Unlimited real estate. The Earth is getting full.
Outside bet? Mercury's poles. There are craters which offer permanent shade, yet nearby (or up a bit) is all the energy one might need. Shame about the Solar gravity well.
Answer: Venus is a prime candidate, it is actually really easy to get to Venus (assuming aerobraking), and as stonemetal points out its gravity is great for humans; unlike the moon and Mars where we don't even know what the long term effect would be of living on those places would be. However, you couldn't hit Venus's surface as it is too hot, too much pressure, and too acidic. It would have to be in the clouds as per this purposed mission http://www.csmonitor.com/Science/2014/1222/How-a-manned-mission-to-Venus-could-actually-make-sense-video Unless there was some serious terraforming effort, but that would take centuries or longer to figure out. The materials to build the cloud cities would likely have to come from else where, though gasses could be had from the atmosphere. Just saw this recent update, actually not much in the way of new info, but a new article on sending people to Venus: http://www.space.com/29140-venus-airship-cloud-cities-incredible-technology.html
Near-Earth Asteroids - Asteroids are actually ideal for a lot of reasons, they don't have huge gravity wells, there aren't as many concerns about potentially destroying pre-existing life as with Mars or some other options, and in the case of Near-Earth Asteroids, their orbits are such that they are easy to get too. They can also be mined in to for radiation shielding, and depending on the size and stability be spun up to create artificial gravity (though that may be more iffy).
The Asteroid Belt- Same as with the Near Earth Asteroids but further out, there are bigger ones such as Ceres, Vesta, etc, the large ones actually make up the majority of the mass of the asteroid belt.
Jupiter has its four big moons, and then a ton of smaller ones. The big ones are dwarf planet size. Callisto http://en.wikipedia.org/wiki/Callisto_%28moon%29 is perhaps the best one to head to because unlike Io, there aren't a ton of Volcanos, Unlike Europa there isn't a likely watery ocean beneath it that could have life, and it has a smaller gravity well than Ganymede, which could also have life. NASA actually identified it as one of the most likely candidate for human colonization: http://www.nasa-academy.org/soffen/travelgrant/bethke.pdf  The radiation on the other moons is quite high.
The thing to realize about going past Jupiter is that Saturn is roughly the same distance from Jupiter's orbit as Jupiter is from the Sun, and it only gets worse from there. Issues of heating and powering a colony become a truly serious problem. If Fusion power is harnessed though, then they become more attractive. Uranus in particular has the lowest gravity, and at one atmosphere of pressure is 90% earth gravity as well as being rich in Helium-3. Also attractive are Titan and some moons that appear to have geothermal activity.
Freeman Dyson thought that comets were the future of mankind, not planets http://en.wikipedia.org/wiki/Colonization_of_trans-Neptunian_objects which would mean that colonization could continue forever and to the stars but society would be fragmented as the distances become too large to travel in any sort of reasonable time period, even communication becomes quite costly.
Answer: Let's look at the different bodies, their pros and cons, and see where that leads:

the Moon
Always a favourite of Sci Fi authors.
Advantages: it's close to home, supply ships, passenger vessels, evacuation/rescue missions are only days away.
Disadvantages: It's got no atmosphere, the gravity is very low (which might be an advantage as well, but many people will get space sickness and suffer osteoperosis, making return to high G earth difficult after spending years there).
Mercury
Advantages: none, unless you want to build a solar powerplant there, and then you'd best make it fully automated.
Disadvantages: searing heat during the day, extreme cold at night. No atmosphere, no radiation shielding. And no, it's not tidally locked (which might leave a narrow band around the terminator that could be used).
Venus
Advantages: none, despite being a favourite of classical SciFi (from before space exploration found the truth about the planet)
Disadvantages: HOT, very high pressure, toxic, acidic atmosphere, high radiation environment
Mars
Another favourite for colonisation.
Advantages: it's BIG, lots of space there. There might be ice and most other things needed to sustain life in its soil. It even has a thin atmosphere that MIGHT be able to sustain some plant life (but definitely not humans).
Disadvantages: It's far away, making it hard to get to. It's COLD, very very cold. The dust storms make it a bad place to be caught out of shelter.
gas giants (dumping them all together, they're similar enough)
Advantages: lots of gas, might be possible to mine it somehow, giving a nice economic incentive.
Disadvantages: high radiation environment, no solid surface to build on (always a problem), atmospheres very violent and probably toxic, plus high pressures. Very low or high temperatures (depending on the planet and how deep you go).
That said, among their many moons there might be some places that could provide interesting places for colonisation. But they'd share the problems of high radiation, low temperatures, and low gravity that we've seen so far.
Pluto
Advantages: none, really. Might work for an underground prison colony but little else.
Disadvantages: extremely far away, no atmosphere, extremely cold, highly excentric orbit makes it very hard to get to or communicate with reliably.
Asteroids
Advantages: easy to get to, tons of materials for building space habitats out of (and enough left over to export to earth at a tidy profit)
Disadvantages: nothing there to build on, you'd have to build your habitat in deep space, and provide it with defenses against impacting rocks as well as radiation shielding. Same disadvantages as any space station, except it will be much bigger...
Comment: I'd probably seperate the gas giants from the ice giants, gas giants have zero credible use for colonization imo, ice giants are essentially super Earths with a large H/He atmospheres, remove them and you might be in business.  Also a special commendation for Jupiter on radiation which is unique in it's intensity compared to the other three.
Comment: @jwenting https://en.m.wikipedia.org/wiki/Ice_giant Neptune and Uranus are considered ice giants.
Comment: @jwenting https://www.nasa.gov/feature/nasa-completes-study-of-future-ice-giant-mission-concepts The paper you site is from 1989, Voyager didn't pass by Neptune until 1989.  The 1990s is when Uranus and Neptune were discovered to be only 20% H2 and He, whereas Jupiter and Saturn are 90%.  See NASA referring to them as ice giants on one of their pages, other pages via a google search of NASA and ice giant for more.  Given it changed in the 1990s it isn't surprising all astronomy text aren't caught up yet.    http://astronomy.com/magazine/superstars-of-astronomy-podcast/2016/04/heidi-hammel
Comment: Re Europa: that's not all you need. The radiation is deadly and also tough on electronics (look at the mission length of JIMO or other cancelled missions, compared to Galileo.
Comment: @BrooksNelson he's talking about our solar system, AFAIK there are no ice giants in it (unless they're way out beyond the Kuyper Belt, far enough so as to not affect the orbits of the known planets and Kuyper Belt objects, which would make them worse to get to than Pluto).
Comment: @BrooksNelson hmm, not mentioned like that in any of the astronomy books I've ever seen. And astronomy.com lists Neptune as a gas giant, as does NASA... https://er.jsc.nasa.gov/seh/neptune.html
Answer: While I think the asteroids would be the next target I'm going to add another Mercury option--because user1987s answer missed a really big factor:
As he correctly stated the poles are cold, the equator is hot.  What he missed is that this translates to a Goldilocks zone between them.  Dig deep enough that you have a constant temperature (this doesn't need to be all that deep) and you have a band around each pole where you do not need heating or cooling other than for load balancing.
Also, others have rejected Mercury because of the high delta-v requirements.  For exploration this is a big deal.  Once you have enough traffic, though, it ceases to be a problem and Mercury becomes easier to reach than the asteroids.  The key is big linear motors.  Once you have enough space traffic you build one on the Moon.  It's wrapped around the equator.  It can put a manned capsule on a transfer orbit to any point in the solar system.  Once Mercury base is big enough you do the same thing there--not only is it a launch system but it's built to grapple a passing spaceship (you'll have good navigation aids, guiding a spaceship on a grazing orbit to get within grapple range certainly could be done), the whole trip is done with only course-correction fuel.  The transfer orbit to Mercury is faster than to the asteroids and the launch windows are more frequent--both of those things say "closer" to me.
Any large enough, airless body could mount such a system.  I haven't worked the accelerations you'll see from a system on Ceres but you certainly don't have access to the whole solar system from there.  Even if it can toss stuff back and forth from the Moon you'll still have to use rockets to get to the other asteroids--and note that while the delta-v requirements for such trips are very low the travel time is long.
Comment: The *Messenger* mission took 7 years to reach Mercury orbit.  It is energetically difficult to reach; same as Saturn actually.  It is far harder to manage than the main belt asteroids!  A spinning tether may be useful for cargo but would be crushing for live humans.  BTW, it found ice in deep polar craters.
Comment: @JDługosz You need something of planetary scale to make such a launch survivable.  That's why I said to wrap your motor around the moon.
Answer: Besides already mentioned Venus (at 50 km above the surface), Callisto (probably the best of Jovian moons), Europa (if you don't mind some digging) and Ganymede (who needs it when we have Callisto?), I'd bet on Titan. Besides its popularity among sci-fi writers, I'd note some other advantages as well:

Much less radiated than Jupiter moons;
Has some gravity (in contrary to Ceres and other asteroids);
Shallow gravity well;
More fuel than on Earth (it rains hydrocarbons!);
Lots of water (and, consequently, oxygen from it);
Can be used as a base for Saturn mining (again, better than Jupiter,
although further);
Nitrogen-rich atmosphere (can be used as a buffer gas);
Methane, ammonia and nitrogen can be used to produce fertilizers;
Most important one: atmospheric pressure is 1.5 of Earth's. Which
gives us:
No need for pressurized habitats and suits (a huge engineering
advantage);
Radiation is blocked out;
Aeronautics is easy to lift-off;
We can strap on wings and fly! What else could we possibly ask
for?

Now for some disadvantages:

Further away than many other targets;
It is cold (in contrary to space vacuum, it is an "active" cold because of atmospheric pressure);
Atmosphere is toxic (as well as on other bodies with an atmosphere);
Gravity is low (again, as almost everywhere).

Overall, Titan is often considered as one of the top-5 places for human colonization. It has its challenges, but a good thermal insulation (parka?) and some oxygen tubes are much easier to engineer and use than conventional spacesuits. Same goes for habitats which don't need to be pressurized and radiation-shielded.


Can I use preclearance for a flight Dublin to USA that connects in Heathrow?

Question: I am booking a holiday to Los Angeles from Dublin. The flights I am looking at will not be direct and have a 1 1/2 hour layover in  Heathrow. I am aware that in Dublin if you are flying to America directly you fill out preclearance forms so that you do not have to do this when you arrive. As I would be flying then from heathrow I would probably have to fill out the forms there. Would I have time in 1 1/2 hours? I can't find information on this anywhere?
Comment: LHR doesn't have US pre-clearance, so on your return flight you'd go through immigration and customs in the USA not Heathrow
Comment: @Gagravarr: That's an answer!
Comment: the form takes about 5 minutes to complete. Ensure you have a pen, your passport, and the US address where you will be staying.
Answer: If your itinerary is DUB-LHR-LAX, then that Dublin and Shannon have US Pre-Clearance facilities is pretty much irrelevant.  Your DUB-LHR flight, while not technically domestic, is essentially similar since you shouldn't have to enter the UK during transit.
You will clear US Immigration and Customs at LAX.  You should expect to get any required forms* from the cabin crew sometime during the LHR-LAX flight.
*CBP has notably automated their processes now.  BA, presumably, will play a video before arrival that describes the process and what travelers are exempt from what procedures.
Comment: Minor correction: the card you fill out in flight is a Customs Declaration, [CBP Form 6059B](https://www.cbp.gov/document/forms/form-6059b-customs-declaration-english-fillable).  Paper I-94 forms are [not used anymore](https://www.cbp.gov/travel/international-visitors/i-94-instructions) for arrivals by air.
Comment: It might be worth emphasizing that LHR does *not* have preclearance, since it seems like OP is under the misconception that it does.  Here is the list of preclearance airports: https://www.cbp.gov/border-security/ports-entry/operations/preclearance
Comment: Yeah, updated.  I've been saying/thinking I-94 for so long.
Comment: okay, I understand this better now and thanks for the helpful answers! Just  to check up, you think that this layover time is long enough to make the second flight considering they are booked within separate airline and I will have baggage in the hold to collect?
Comment: That's a totally separate question and there are many factors involved.  You should open a new thread, but it will likely get redirected to many similar questions and answers.
Comment: While DUB-LHR is an International flight, for immigration purposes, more than likely, the OP will not have to leave transit zone so they will not have cross the UK border.
Answer: The question is base on a misconception of US preclearance. For practically every country, once you arrive on their soil from outside[1] you are subject to passport controls and customs inspection. This means that:

you can only arrive at 'international airports', i.e. those that have these facilities
if there are a number of flights arriving at the same time, customs and immigration may be very congested.

Preclearance was introduced to combat these points, originally by a request of American Airlines who presumably wanted to operate flights from Toronto to 'non-international' US airports (where immigration and customs cannot be performed on arrival due to lacking facilities). Its concept is to 'outsource' all immigration and customs checks to foreign soil, before a plane's departure. This renders an international arrival something that seems like a domestic arrival from the arrival airport's point of view. And it makes sense from a time-economic point of view: passengers typically arrive at the departure airport many hours before their plane leaves, so why not use that spare time so that they can make quicker connections on arrival?
The big downside to preclearance is that it requires those facilities at the departure airport and it also requires a bilateral agreement between the US and whichever country the airport is in to allow for US CBP to perform their duties in foreign countries.[2]

Your suggested itinerary, however, completely defeats the idea of preclearance. Say you are in a plane with 200 other passengers on your way to Heathrow from Dublin. You might be travelling on to the US and maybe ten others, too. That leaves 190 passengers in that plane not going to the states that don't need to (and don't want to, and must not) go through preclearance — they will not enter the US.
You could make arrangements to have somebody else smuggle some customs-relevant item onto your Dublin–Heathrow plane that you then intend to get past the US customs as you already went through preclearance. That would create a massive loophole. Therefore, preclearance is only possible for those flights that depart for the US without further ado.
And what about your Heathrow–US flight? Well, Heathrow airport does not have preclearance facilities.[3] So you cannot go through preclearance there.

[1]: Sometimes, outside does not only mean outside the country but outside of a greater set of countries. E.g. Arriving in Germany from the Schengen area or in the UK from the Repulic of Ireland (as part of the Common Travel Area) is basically treated as domestic travel.
[2]: Typically, the US CBP has less possibilities when operating on foreign soil. For example, they do not have the power to arrest travellers outside of the US, and they cannot force people to allow searches. They can, however, prevent boarding.
[3]: Plans exist to extend preclearance to a number of additional airports; Heathrow is amoung them. (Homeland Security press release)


solving triangles

Question: I have $\displaystyle\frac{56.851}{\tan(42.0892^\circ)}$, how do I figure that out on a calculator?
I tried and I keep getting syntax error and I don't know how to make degrees.
Google was no help either.
Comment: The teacher is paid to have time to answer your questions.
Comment: Did your calculator come with a user's manual?
Comment: No, it is somewhat old and there is nothing online that I can find.
Comment: If you are doing homework, just use calculator.com or any online calculator.  If you need to figure ut how to use the calculator for a test or some other type of assessment, ask your teacher.
Comment: It is for a test and for homework, not sure if the teacher has time to answer this question.
Comment: What specific model of calculator are you using?  And what are you typing in (what exact keystrokes)?
Answer: If you have a scientific calculator, there is usually a button that looks like deg/rad/grad.  What this button does is sets the mode for doing trig functions.  When it is in deg, it assumes you are entering angles in units of degrees (360 in a full circle, nice for engineers), rad for radians ($2\pi$ in a circle, the mathematician's choice), and grad for gradians (400 in a full circle, which I guess is good for people who love the metric system).  As long as you are in the right mode, you are automatically specifying your units.
If your calculator does NOT have such a setting, then you should convert manually.  $x$ radians is $x\cdot \frac{180}{\pi}$ degrees.
Answer: First make sure your calculator is set to degrees or do the conversion mentioned in the other posts.
You shouldn't need to put in the degrees symbol if the calculator is set to degrees (ie you can see either D or Deg somewhere on the display) if instead you can see R, Rad, G or Grad then you need to set it to degrees instead. If it is set to degrees then the number on  which a trig function is operating is already assumed to be in degrees. Your question gives the angle in decimal degrees so you don't need to worry about converting to degrees, minutes and seconds and back again (if you don't understand the last sentence don't worry you probably don't need to).
Older calculators required you to enter the value of the angle 42.0892 first then press the trigonometric button to get the result. Normally if you can see the calculation as you are typing it in then you can just do the calculation in the natural order otherwise you need to do the calculations bit by bit and build up to the final steps.
As a test (with the calculator set to degrees) type 45 and press the tan button, if you have the older style of calculator this will return a value of 1 (the answer to doing tan(45)).
If this is the case then I would work out your calculation using the following steps:

Make sure your calculator is set to degrees
Type in the angle 42.0892
Press tan
The answer is the tan of 42.0892, make it into a reciprocal (there's probably a $\frac{1}{x}$ button or $x^{-1}$ button somewhere on the calculator)
Now multiply the resulting value by the numerator (56.851)
Press equals that should be your answer.

If you can't see a reciprocal button, put the answer to tan(42.0892) into the calculator memory, enter 56.851 and divide it by the stored value.
If you do it right you'll get an answer of 63 rounded to to 2sf (I won't give you the full answer as you should write down the full display and then round it to a suitable degree of accuracy yourself).
Answer: Use the $\pi/180$ conversion factor to convert degrees to radians.
Answer: Try Wolfram|Alpha.

solving triangles


Can the VGA port of the laptop be used as input port?

Question: A few days ago I had a problem installing a video conferencing system, as I was unable to take the output of the codec display on a TV for some reasons. I was wondering could I have used the VGA port of the laptop as the display input just like that of a TV? If Yes how?
Answer: No, VGA ports on a laptop are output only.
Answer: To expand on AJ Henderson's answer, it would be extremely rare to find combined output/input ports for A/V on a computer, and certainly not combined input/output VGA. This is because the underlying technology to receive and process video is very different to that required to send it and uses high-frequency electronics which tend to be very picky about how they are laid out and connected. As a result adding both send and receive hardware to the same physical port is impractical, bordering on impossible. There are also implications of cost, naturally adding anything to a laptop that's not really needed by the majority of users will drive the price up, and nobody wants that!


Logins Getting Stuck on Wallpaper After Ubuntu 14.04 Base and Security Update (but not when logging in as Guest)

Question: As the title says, after an update sometime last week, logging into my user account only gets as far as changing the background from the login screen's standard to my personal wallpaper.
No dashboard or anything else appears: I can only move my mouse pointer around and fruitlessly make selection boxes and right-clicks.
There are many questions with similar problems and I have tried all of the following already (in order):
I went into a terminal with Ctrl+Alt+F1 and ran apt-get update and apt-get upgrade to upgrade 8 packages I had which were still marked as uninstalled. They seem to have installed successfully but the problem persisted after a reboot.
I then tried installing compiz-settings manager as per the instructions at Unity doesn't load, no Launcher, no Dash appears and using it to re-enable the Unity Plugin. Still no noticable change after a reboot.
I have also tried uninstalling and reinstalling lightdm, ubuntu-desktop and unity via the terminal, also with no noticable changes after a reboot.
I renamed my .Xauthority file so that a new one would be created as per the instructions at Ubuntu gets stuck in a login loop. That also did not solve the problem. The Xauthotity file is owned by me. It doesn't look like there is anything wrong in my .profile file either.
Lastly, I found a suggestion on one of these many similar threads that I should disable the desktop icons. I ran some command in the terminal to the effect of "gnome show-icons false" and after that for some reason the wallpaper doesn't even appear now and when I tried to reverse the change by running the command again with the value "true" instead of false I got an error message to the effect of "unable to change" due to permissions or settings or something.
Important points: I am able to login as a guest with absolutely no problems at all, which suggests to me that this is not the result of a graphics driver problem.
I freshly installed Ubuntu 14.04 (64-bit amd) around the end of May: this was not an upgrade from an old version. I have had no problems until now.
I would greatly appreciate any assistance which you could provide.
Update: 08-30-2014
After a week, I logged back into a terminal and performed some more apt-get updates and upgrades, still to no avail, but I was able to make a new user account within the terminal and log in using the new account with little more than a slight delay!
I have already checked/removed my old .Xauthority and .profile files to make sure that they are not the problem, and I do not know what other user-specific information may be causing this.
If no one can help me find the source of this problem, I would also appreciate any suggestions as to an easy way to migrate my data over to my new, working account from my old one. For example, my applications, my software, my virtual machine, etc.
Any help would be greatly appreciated.
Comment: I have the same issue, can't seem to find the answer online as well
Comment: same problem here.

Try http://askubuntu.com/questions/17381/unity-doesnt-load-no-launcher-no-dash-appears
Answer: <code>nautilus --force-desktop &
</code>
Found something that says by running the above line will get you wallkpaper back.  Also, possibly gnome-tweak-tool will also fix the issue


How much does it cost to enter and leave the same station (JR line, Tokyo)

Question: I'm going to pick an item up from someone in Tokyo. Problem is, it's about an hour away and therefore the journey is quite expensive. So he's agreed to meet me at his station on the platform so I don't need to 'tap out'. This is on the JR Chuo-Sobu line. How much does it cost for me to tap back out at my entrance station (I know it's not free, but I have no idea what to search online to find this information).
Comment: People wish to do this often enough in the SF Bay Area that there is indeed a fare for a round-trip where you don't exit the gate at the far side. It's called the Excursion Fare. Three hours maximum, currently $5.55. That's about 2.5 times the lowest possible one-way fare, but significantly *less* than the longest one-way fare. I think investigating whether Tokyo has a similar fare is more productive than suggesting the OP is attempting to evade the fare entirely. (I wish I could -1 a comment.)
Comment: While it may seem 'dodgy', it's perfectly legal in many other countries which is why I asked if it is possible in Japan as well. The platform ticket says it is. Either way, best method I've found so far (as I do not want to leave the station on the other end, hence I don't want to pay a round long trip price) is to return to one stop before my departure station and exit there - 1 stop 1 way price.
Comment: @KeirSimmons As someone who takes some variation of Japanese trains daily (Tokyo Metro, JR, Tokaido Shinkansen, Kobe Metro Railway to name a few in the last week), I can tell you that it all depends on how you approach it. I have had to go from my home station all the way to the end of the line to retrieve lost property and the office was outside of the gates. Explaining this to the Station Staff usually gets you through the gate without tapping off / using your ticket. Returning to your station and explaining the situation to the guard there, usually results in negation of your trip cost.
Comment: cont... However in this case as you are not retrieving something from the train company themselves, when tapping out at your origin station, the gates will automatically block you from leaving. When you present yourself to the guard they will ask what your situation is. Depending on what you tell them (however honest / dishonest it is) is in most cases, what they will deduct from your card before letting you go.
Comment: There is no such fare in Tokyo. Agree with fkraiem's -1 ...  Might as well suggest to the OP to buy the children's version of the platform ticket at half-price the adult fare.
Answer: It should go without saying, but since some people seem unclear on the concept, I state explicitly that riding a train without paying the correct fare is not just "dodgy" or any other euphemism you can think of, but a violation of the Article 29 of the Railway Act (not to be confused with the Railway Business Act) and also constitutes fraud under Article 246 of the Penal Code.

That being established, what is the correct fare when you enter and leave from the same station? It depends on the actual departure/arrival station and route you take, so it is impossible to answer the question without knowing them (but it can certainly not legally be done with just an entrance ticket)
Now, the general principle is that the fare is to cover the costs of you riding the train, not of you passing through the ticket gates, and so whenever you ride a train, you must pay the corresponding fare, regardless of whether you exit the gates. Note for example that "station entrance tickets" very explicitly state that you may not ride a train*.

旅客運賃・料金は、旅客の実際乗車する経路及び発着の順序によつて計算する。
The fare is calculated based on the route actually traveled by the customer, as well as the order of departure and arrival. (link)

However, the usual exceptions apply, including the one that says that if your route is contained entirely within one of five "large city" zones, then regardless of the route written on your ticket, you can use any other route that you want between the same departure and arrival points. In practice, this means that you can buy a ticket for the cheapest possible route, and actually use any other one that you want.
Example 1: suppose I want to make one round of the Yamanote line starting and ending at Tokyo station. A possible route from Tokyo to Tokyo is via Kinshicho and Akihabara, so I can buy** a Tokyo-Kinshicho-Akihabara-Tokyo ticket and make my Yamanote circle trip, no problem.
This is further complicated by the fact that not every route is a route, so to speak. In particular, for ticketing purposes a route may not contain any loops or duplicated sections, and in your case you may well have at least one of those, since you want to go to some particular station and back.
Example 2 (loop): Suppose I want to do Kinshicho-Ochanomizu-Kanda-Ueno. Because this has a loop (Akihabara-Ochanomizu-Kanda-Akihabara), the correct fare for this trip is Kinshicho-Akihabara plus Akihabara-Ueno and not just Kinshicho-Ueno. In general, when you complete a loop, your trip is automatically "cut" into two separate trips at the last station of the loop.
Example 3 (duplicate section): Suppose I want to go from Tokyo to Atami and back. Because this will require duplicating the section between Atami and Chigasaki, I must pay both Tokyo-Atami and Atami-Tokyo. In general, when you "backtrack" at a station, your trip is automatically "cut" into two separate trips at that station.
Example 4: However, I can go from Tokyo to Chigasaki and back with my Tokyo-Kinshicho-Akihabara-Tokyo ticket, because it can be done without any loop or duplicate section: I can go from Tokyo to Chigasaki via Shinagawa and Yokohama, and then back via Hachioji, Shinjuku, and Akihabara.
Note that all those examples are if you do not exit the ticket gates, as per OP. As I have mentioned elsewhere, tickets for travel within the five large city zones do not allow exiting the ticket gates before your arrival point (stopovers).

* Now, like many other things that are in principle not allowed, you may or may not be able to talk an agent into letting you get away with it, possibly by feigning ignorance (especially if you are a foreigner). Personally, I find this practice abhorrent.
** A ticket with the same departure and arrival points can be purchased at ticket offices only. Not at ticket machines, online, or via an IC card.
Comment: @KeirSimmons Again, this is fare escape and unequivocally illegal; flagged as such.
Comment: No it's not. Put yourself in the shoes of a completely unsuspecting mother (as a random example) taking her kid to eat at Tokyo station. There are many restaurants there which are within the barriers. After eating she decides to hop back on a train en-route to DisneySea. She stopped off at Tokyo but never tapped out - it wasn't part of her journey to. This sort of thing is quite common with the number of shops/ restaurants within ticket barriers. Do you expect the mother to tap out of tokyo station, and then tap back in to continue with her journey? Of course not. It's rather a flawed system.
Comment: @TheWanderingCoder Possibly a bad example then. I'll return to the unsuspecting mother boarding a Chuo train from Koenji, taking her kid to Tokyo station to eat, and then going back on a Chuo to Nakano to take her kid to Nakano Broadway. In essence, they've only gone from Koenji to Nakano (1 stop) and never tapped out in Tokyo. Is it her job to go out of her way to tap out at Tokyo and back in to eat, or is it JR's to police the possibility? For example in London we have Oyster tapping points within barriers to tell the system of the specific route you're taking without exiting the barriers.
Comment: @KeirSimmons Technically it is her job to tap out at Tokyo and according to "apparent" customs the honest citizen will do this (in practice I would argue this doesn't happen). Further, if noticed (extremely unlikely chance) JR can and will confront someone. Although fines can be issued, the normal reprimand is a stern talking to. Getting back to your question, when attempting to exit the barrier, the ticket gates will stop you from leaving as you will have an invalid fare (you can not enter and exit from the same station unless you have an unlimited travel pass).
Comment: ...You will have to go and speak to the ticket gate employee who will usually ask where you have been and charge you to and from that station. Obviously if you lie there is no way of telling what happened short of calling the station you claim to have gone to and checking surveillance, however they do take time taken (your entry time is printed on your ticket / stored on your IC card) and if it doesn't roughly match up, they will usually phone your apparent arrival station to confirm your story - and they *do* do that).
Comment: Can't OP simply exit one station before his station and then check back in?
Comment: @JonathanReez Can you be more precise? If you exit the station, then certainly you must pay the fare between your entering and exiting points...
Comment: Yeah, but if OP only exits one station before his departure point, he would only pay for the cheapest possible fare.
Comment: @JonathanReez Assuming there are no loops or backtracking, yes. You can do this for example if you want to do almost a full run of the Yamanote: buy a ticket to the next station in one direction, and actually use the other direction.
Comment: @jonathanreez: yeah it's possible. I for example live in Koenji. I can take a chuo all the way to Tokyo, eat within the ticket barriers there and come back to Nakano (1 stop before koenji) and exit there. Probably not how they intend it to be used, but it's doable. Similarly I could go all the way to Koenji and say I didn't board a train and pay the equivalent of a platform ticket. Again, up to the 'user' to decide what is morally right and wrong before doing either of these.
Comment: @KeirSimmons Unless said mother was coming from the direction of Maihama, that could be considered transfer as she is still paying a full fare section A > B and travelling said section.
Answer: A platform ticket is called a 入場券 (nyuujooken), it allows you to enter the platform area to see people off.
Suica unfortunately cannot be used as a platform ticket. If you try to tap out at the same station, it won't let you.
Platform tickets can be bought at the paper ticket vending machines -- and you can use your Suica to buy paper tickets.  They are ¥140 for most of Japan (see https://www.jreast.co.jp/kippu/18.html).
Comment: However, departing the station with a platform ticket is technically not allowed.  In practice, of course, there's no enforcement as long as you stay within the ticket gates, since (local) Japanese trains do not have inspectors.
Comment: If the OP is outside of Tokyo at a smaller station, it might be very hard to convince the station master that over two hours were spent at the home station when exiting. But FWIW, if the two hour limit is surpassed they can sell you a separate platform ticket for every two hours.
Comment: Did it several times on Chuo line in Tokyo (Higashi-Nakano St.) - the procedure was to buy the cheapest ticket, give it to man-at-the-gate who stamped the ticket, and leave also through a manned gate. I guess the 入場券 would be specifically sold in areas where the fare to the nearest station exceeds the amount specified on the linked page. There is no such need in Tokyo or Osaka where stations are densely packed. The other time I had to return to my company just after entering Tokyo Metro. Also no problem at the manned gate, got Suica charged for the cheapest fare (160 yen at the time).
Answer: First up, this is a bit dodgy and I'd suggest perhaps just paying the fare...
As for the technicalities - you won't be able to tap out with Suica at the same station on JR, you'd need to go to the attendant and ask them to do it manually. If it's 2 hours after you tapped in, they may ask questions.
You can buy paper 'platform tickets' to see off people at some stations without traveling, and as there aren't conductors on trains you could get away with this also.
Comment: How is it up there on your lofty steed?
Comment: This is not "dodgy", it's fare escape and probably illegal.
Comment: Note that JR platform tickets are generally valid for two hours.
Comment: Not great because I'm among those given a bad name by tourists breaking all kinds of rules.
Comment: With my pasmo 定期券 (commuter pass), I am able to go in/out of stations along the route freely; even exiting the same station. I don't know if this is pasmo-specific, railway specific (I ride a smaller line, not JR) or if all passes operate similarly. Of course, using a pass to travel in the other direction and back could result in the confiscation of the pass; whereas if you're caught using the platform ticket the penalty is likely limited to some small multiple of the normal fare.
Comment: It's not breaking rules - platform tickets exist for this reason.
Comment: @Kent It is Japan-wide Commuter / School Pass specific. However certain passes (Metro 24hr pass etc.) also allow this (within the networks they service). You would not lose your pass for travelling however many times you want, for however many days you want within the passes validity as you have essentially already prepaid travel from any and all sections between A > B.
Comment: @fkraiem source for this being a "fare escape"?
Answer: First of all, this is not dodgy.
It is legally fine to ride a train without paying anywhere you want unless you exit the station or ride in reserved cars.
All you need is to visit the guy in the window near the gates when exiting and explain that you did not exit the station on the other end. They will remove the 入場券 price (about 140 yen) from your Suica/Pasmo and that's it. You do nothing illegal, so even if they ask why did it take 2 hours, you could kindly explain.
Comment: You only pay at the moment you check out of the train system. If you check in and check out at the same section within the same day you only pay 入場券. It does not matter where you travel. I am not sure what sources are possible here. If you are trying to press on the moral side of this action I would say that riding somewhere without checking out is pretty useless thing in most cases, so there is very little incentive to abuse this for anyone. And that's why no one really cares.
Comment: @rilakkuma I frequently ride to Tokyo for some ramen within the barriers and then return home. I guess you could say this is abusing the system, but I guess that's down to one's moral compass.
Comment: I link to a website where the railway company states that you only need to pay for entrance and exit would be a good start. I have never seen one of those, I have seen plenty websites stating that you pay for the distance traveled. (But I have never tried to look for any Japanese ones.)


Email send options to set a future delivery date?

Question: Is it possible to set a future delivery date for a Lotus Notes email message?  I would like to compose a message but have it delivered at a future date automatically.
Answer: There is the option of using a reminder on your calendar. You can tell a reminder to send and email as an alarm. The subject of the reminder will be the subject of the email concantenated with "Alarm: "+your subject+ the date and time of the reminder.
The text in the Description will be in the body of the email.
Answer: I'm not aware of any built-in feature within Notes that supports that, but depending on your setup, it might be possible to make an Agent that would force delivery at a later date.
Comment: This is true.  We encountered this request from a client a while back, and direct from the horses mouth (IBM) this functionality is not supported at this time.  But the problem was solved using custom code written by our Notes Developers.
Answer: EDIT: This was posted before the OP's edit to include Lotus Notes. The information will be kept here regardless for any nessecary future reference.
If you are using Outlook 2007 (may work in 2010, unsure about 2003) you can click on "Options" while composing the message and set a "Do Not Deliver Before" Time and date.
You may want to send a test message with this method as e-mail is an unreliable beast.
Answer: Go to Calendar → New → Reminder → Notify me → Send notification with subject.
Answer: Using Lotus Notes, provided your connection is up/active, you could disable replication, send the message, and set the replication for the time desired.
The message would then sit in your local mailfile until the replication 'fires off'.
To note: I believe it would carry the time/datestamp of when it was generated instead of delivery date.
Answer: Lotus Notes is much more than an email program. It is a sophisticated enterprise solution for large volume corporations. It has thousands of features so it really cannot be compared with a 2 dimensional application such as outlook.
That being said this feature does not exist out of the box - unless you want some sort of hack send-a-reminder-instead solution. There are numerous ways (unlike Outlook):

Install autohotkey and write the functionality yourself
Install Firefox / greasemonkey use the webpage and write the functionality yourself
Study the Lotus Notes API for 10 years and write the functionality yourself
Get the Dominoes Server to enable SMTP, install a standard email client and use the existing functionality
Answer: The functionality does not exist in Lotus Notes as it does within Outlook.  As an anecdote though, an insightful user I knew was able to put something together using Grease Monkey and the Lotus Notes' API.  Hope this helps & good luck!
Answer: I'm using LN 8.5, and there is a function that allows you to send a "timed delivery memo," where LN uses "memo" the same as "message."  Perhaps this feature needs to be enabled by your Domino admin, so it may or may not exist for you.  Try this...
Create > Special > Timed Delivery Memo
This will open a message (memo) with an extra option to specify a date and time for delivery.