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UPSC Prelims 1998 · World Geography · Earth in Space
One Astronomical Unit is the average distance between
- (a) Earth and the Sun
- (b) Earth and the Moon
- (c) Jupiter and the Sun
- (d) Pluto and the Sun
Show the answer and explanation
Answer: (a) Earth and the Sun
1 AU = mean Earth–Sun distance (~150 million km).
The idea
An astronomical unit is a distance scale suited to the solar system. It is based on the Earth–Sun separation, so planetary orbits can be compared without writing very large kilometre values. It measures length, not time.
Why the others are wrong
(b) Earth–Moon is ~384,000 km.
(c) Jupiter is ~5.2 AU from the Sun.
(d) Pluto is ~39.5 AU.
Also know
Since 2012, one AU has an exact defined length of 149,597,870,700 metres. A light-year is the distance light travels in a year, and is useful for distances between stars. A parsec is about 3.26 light-years and comes from measuring a nearby star’s apparent shift against distant stars.
🔒 1 AU ≈ 149.6 million km; light takes ~8.3 minutes.
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