Which one of the following is a reason why astronomical distances are measured in light-years?

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UPSC Prelims is a competitive examination conducted in India. This question is from the 2021 UPSC Prelims Science & Technology paper.

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Question

Which one of the following is a reason why astronomical distances are measured in light-years?

Accepted Answer

Correct Answer: D — Speed of light is always same.Step-by-step Solution:Astronomical distances are measured in light-years because the speed of light is constant in a vacuum (approximately 3,00,000 km/s) throughout the universe. This constancy allows astronomers to use the distance light travels in one Earth year (about 9.46 trillion km) as a reliable and convenient unit for measuring vast inter-stellar and inter-galactic distances. ✓Other options are incorrect: distances between stars do change (proper motion), gravity varies, and light can be bent by gravity (general relativity).Why other options are incorrect:Option A: Stellar distances do change due to motion of stars and expansion of the universe.Option B: Gravity varies with mass and distance; not constant.Option C: Light bends in gravitational fields (gravitational lensing).Key Concept: A light-year is a unit of distance, not time. It is defined based on the invariant speed of light in vacuum (Einstein's theory of relativity). Other astronomical units include astronomical unit (AU — Earth-Sun distance) and parsec (pc).

Which one of the following is a reason why astronomical distances are measured in light-years?

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Which one of the following is a reason why astronomical distances are measured in light-years?

Master UPSC Prelims with Our Test Series

More Questions from Physics Concepts – Laws, Motion, Optics & Thermodynamics

Frequently Asked Questions