Question

Light year is a unit of
A. Speed
B. Speed time
C. Speed/time
D. Time

Answer 1

- Hint: On earth we can define distance in terms of km or m. But if we need to define distance between galaxy distance in terms of km or m is not easy to write. So for that astronomers use different units. Hence we can say in astronomy, large units are required to express the distances between different objects. One such unit is light year.

Complete step-by-step solution -
One light year is defined as the distance traversed by light in vacuum in one year. This unit is efficient for large scale computations of distances. Speed of light in vacuum is,
\[c=299792458\,\text{m/s}\]
The internationally recognized definition of light year is the distance covered in vacuum by light in one Julian year, composed of \[365.25\] days. Therefore,
1 light year \[=\text{ }(299792458)\text{ }\left( 365.25 \right)\text{ }m\text{ }=\text{ }9460730472580800\text{ }m\]
Clearly, the light year is a distance which is the product of speed and time. Hence, the correct option is: (B) speed time

Note: Speed of light in vacuum is a universal constant. Large scale computations require a large unit of distance. The distance covered by light in one year is a huge distance and such distance scales are only used in Astronomy. So we can say to represent astronomical distance we use light year unit