Bailyn, Charles. ASTR 160: Frontiers and Controversies in Astrophysics, Spring 2007. Yale OpenCourseWare: Astronomy, Accessed 20/9/14 http://oyc.yale.edu/astronomy/astr-160/lecture-6 License: Creative Commons Attribution-Noncommercial-Share Alike 3.0 license The class begins with a discussion on transits – important astronomical events that help astronomers to find new planets. The event occurs when a celestial body moves across the face of the star it revolves around and blocks some of its light. By calculating the amount of light that is being obscured astronomers can obtain important information about both star and planet, such as size, density, radial velocity and more. The concept of planetary migration is explained in order to better understand the dramatic differences between bodies in the Inner and Outer Solar System.