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UPSC 2021: Which one of the following is a reason why astronomical distances are measured in light-years?
(a)Distances among stellar bodies do not change.
(b)Gravity of stellar bodies does not change.
(c)Light always travels in straight line.
(d)Speed of light is always same.
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Not attemptedCorrect Answer: (d) Speed of light is always same.
A light-year is defined as the distance light travels in vacuum in one Julian year; because the speed of light in vacuum is a fundamental constant that remains the same everywhere, this unit gives astronomers a convenient, unvarying yardstick for very large inter-stellar distances. Hence the reason is the constancy of light’s speed, making option (d) correct. ([en.wikipedia.org](https://en.wikipedia.org/wiki/Light-year?utm_source=openai))
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Frequently Asked Questions
What is the correct answer to this UPSC 2021 Science & Technology question?▼
The correct answer is option (d): Speed of light is always same.. Watch the detailed video explanation in our Sherlocking Prelims course on UnlockIAS.
Which year was this Space Technology & Astronomy question asked in UPSC Prelims?▼
This question was asked in UPSC CSE Prelims 2021, GS Paper 1, as Question 76. It falls under Science & Technology > Space Technology & Astronomy.
What is the difficulty level of this UPSC question?▼
This question is rated "easy". It tests basic recall and most well-prepared aspirants should answer it correctly.
How many UPSC Prelims questions have been asked from Space Technology & Astronomy?▼
UPSC has asked 69 questions from Space Technology & Astronomy (under Science & Technology) across multiple years. Visit the topic page to see the full list and year-wise trends.