Why is a light-year a unit of distance rather than a unit of time?
Show answer & explanation
Answer: Distance light travels in a year
Distance light travels in a year ✓ — Correct! A light-year is a unit of length used for cosmic distances. Light travels about 300,000 km per second, so in one Julian year it covers roughly 9.46 trillion km (5.88 trillion miles). Proxima Centauri is 4.24 light-years away, and the Andromeda galaxy is about 2.5 million light-years away. Because light takes time to reach us, we see distant objects as they were in the past.
Measurement of star brightness — Wrong. Brightness is measured in magnitudes, not light-years. A light-year measures distance—how far light travels in one year through space.
Time for light to reach Earth — Wrong. A light-year is strictly a unit of distance, not a unit of time. It is defined as the distance light travels in one year, which is about 9.46 trillion kilometers.
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