If astronomers want to measure the mass of a star or a planet, they usually rely on the orbital motion of a satellite or binary companion. Which of these is the basis for a mass measurement of a solitary mass?
A) time dilation
B) length contraction
C) gravitational redshift
D) geodesics

Question

Quizplus · Accepted Answer

Gravitational redshift is the phenomenon where light or electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum, by the gravity of the object emitting the light. This effect is a prediction of Einstein's general theory of relativity and can be used to measure the mass of a solitary object, such as a star or planet, by observing the amount of redshift in the light coming from the object. The greater the mass of the object, the stronger its gravitational field, and the more pronounced the gravitational redshift.

If Astronomers Want to Measure the Mass of a Star