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-7 License: Creative Commons Attribution-Noncommercial-Share Alike 3.0 license Class begins with a problem on transits and learning what information astronomers obtain through observing them. For example, radii of stars can be estimated. Furthermore, applying the Doppler shift method, one can find the mass of a star. Finally, a star's density can be calculated. A second method for identifying planets around stars is introduced: the astrometry method. The method allows for an extremely accurate assessment of a star's precise position in the sky. Special features of the astrometry method are discussed and a number of problems are solved.