Which one of the following is a reason why astronomical distances are measured in light-years?
Which one of the following is a reason why astronomical distances are measured in light-years?
Distances among stellar bodies do not change.
Gravity of stellar bodies does not change.
Light always travels in straight line.
Speed of light is always same.
Solution
A light-year is the distance light travels in vacuum in one year. Since the speed of light in vacuum is a universal constant (approximately 3 x 10^8 m/s), it provides a reliable yardstick for measuring vast astronomical distances.