The look-back time of an object is directly related to its:
A)mass.
B)distance.
C)luminosity.
D)size.
E)composition.

Question

Quizplus · Accepted Answer

Look-back time is the amount of time it takes for light to travel from an object to Earth. Since the speed of light is constant, the distance of an object determines its look-back time. Therefore, the best choice is B, distance. The look-back time is the amount of time it takes the light from an object to reach us. Since the speed of light is constant, the look-back time is directly related to the distance of the object. Therefore, option B is the correct answer. The mass, luminosity, size, and composition of an object do not directly affect its look-back time.

The Look-Back Time of an Object Is Directly Related to Its