When light is emitted by a star, it travels to regions of higher gravitational potential. Conservation of energy leads to a resulting change in energy of the photon, increasing its wavelength. This effect is known as the gravitational redshift. In this Demonstration, the wavelengths are as measured by an observer at infinity for a photon emitted at the distance from the star controlled by the distance slider.
A. Einstein, "On the Influence of Gravitation on the Propagation of Light," Annalen der Physik, 35, 1911.
Wolfram Demonstrations Project
Published: October 19 2009