UPSC Prelims 2021·GS1·science-and-technology·science and technology

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

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Last updated 23 May 2026, 3:31 pm IST
  1. ADistances among stellar bodies do not change.
  2. BGravity of stellar bodies does not change.
  3. CLight always travels in straight line.
  4. DSpeed of light is always same.Correct

Explanation

The reason astronomical distances are measured in light-years is primarily because the speed of light in a vacuum is a universal constant. Light travels at an incredibly high but finite speed (approximately 299,792,458 meters per second). Because of the immense distances involved in astronomy, using conventional units like kilometers or miles would result in unwieldy large numbers. A light-year, defined as the distance light travels in one Julian year, provides a convenient and comprehensible unit for these vast scales. The constancy of the speed of light makes this unit reliable and uniform across the universe, making it an ideal fundamental measure for cosmic distances.
science-and-technology: Which one of the following is a reason why astronomical distances are measured in light-years?
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