Bailyn, Charles. ASTR 160: Frontiers and Controversies in Astrophysics, Spring 2007. Yale OpenCourseWare: Astronomy, Accessed 22/9/14 http://oyc.yale.edu/astronomy/astr-160/lecture-13 License: Creative Commons Attribution-Noncommercial-Share Alike 3.0 license Class begins with clarification of equations from the previous lecture. Four post-Newtonian gravitational effects are introduced and discussed in detail. The first of these is the so-called Perihelion Precession, which occurs when the major axis of a planet's elliptical orbit precesses within its orbital plane, in response to changing gravitational forces exerted by other planets. Secondly, deflection of light is described as the curving of light as it passes near a large mass. Gravitational redshift is explained as a frequency effect that occurs as light moves away from a massive body such as a star or black hole.