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Official Soldier GD Paper: [Bihar Regt Centre, Danapur Cantt] - 28 March 2021

Option 4 : Light year

The correct answer is __Light year.__

__Key Points__

- Light year: The distance travelled by light in one year is called a light-year.
- It is a unit of astronomical distance.
- 1 light-year = 9.461 trillion kilometres which is a very large distance.
- Hence option 2 is correct.

** Additional Information**.

- As defined, a light-year is a distance travelled by light in free space in one year.
- Also, the speed of light = \({3* 10^8} m/s\)
- Time = 1 year or 365 days
- Hence, by formula Distance = Speed / time
- We got that, one light-year = \({9.46* 10^{15}} metres\)
- Or, 1 light-year = 9.461 trillion kilometres.