     material:
       title: "How else can we discover planets? - Direct Imaging"
       text: """
-        <p>The separation and extreme difference in brightness between exoplanets and their host stars makes it very difficult to image them directly. However, there are a handful of exoplanet candidates  that have been discovered this way. All of them have very large radii and lie in distant orbits.</p>
+        <p>The small separation and extreme difference in brightness between exoplanets and their host stars makes it very difficult to image them directly. However, there are a handful of exoplanet candidates  that have been discovered this way. All of them are very large and lie in distant orbits.</p>
         <p>Above is an picture showing the directly imaged exoplanet candidate orbiting in the debris disk around the star Formalhaut.</p>
         """
       figure: "./images/mini-course/slide-22.jpg"

  {
    course_number: 16
    material:
      title: "How else can we discover planets?"
      text: """
        <p>The transit method is a very simple and effective method for discovering planets, but it is not the only one used by astronomers. Let’s have a look at some of the other methods:</p>
        <strong>THE RADIAL VELOCITY METHOD</strong>
        <p>As a planet orbits a star its gravitational pull moves the star around. Therefore at some points the star is moving towards us and at other points it is moving away from us. We can measure the speed of this movement by examining the light from the star. When moving towards us the star’s light becomes more blue, and when moving away, more red. The faster the star is moving, the more massive the planet. For example, Jupiter moves the Sun at 12.7 m/s (slightly faster than Usain Bolt can run), whereas the effect of the Earth is 100 times smaller, making it much easier to detect larger planets.</p>
        """
      figure: "./images/mini-course/slide-16.jpg"

    material:
      title: "The Kepler Mission"
      text: """
        <p>The Kepler space telescope was launched by NASA in 2009. It is named after 17th century German astronomer Johannes Kepler, who is best known for developing the laws of planetary motion. For 4 years it stared at a patch of sky 100 square degrees in area (500 times that of the full Moon) in the constellations Lyra, Cygnus and Draco, looking for the tell-tale dips in brightness caused when a planet passes in front of its host star. It is these brightness measurements you are examining on Planet Hunters.</p>
        <p>The 2nd phase of the mission (K2) began in 2014. During this phase the telescope will be looking at new patches of sky every 75 days, providing a fresh set of data for you to search through on Planet Hunters.</p>
      """
      figure: "./images/mini-course/01-KeplerHR_sm.jpg"
