UPSC Prelims 2006 Q37: Science & Technology – Space Technology & Astronomy
What is the approximate mean velocity with which the Earth moves round the Sun in its
orbit?
- (a) 20 km/s
- (b) 30 km/s
- (c) 40 km/s
- (d) 50 km/s
Answer: (b) 30 km/s
Explanation
Earth's mean orbital velocity around the Sun
The Earth covers an orbit of about 940 million km in one year, giving a mean speed of about 29.8 km/s.
| Option | Verdict |
|---|---|
| 20 km/s | Too slow |
| 30 km/s | Matches the mean orbital speed of about 29.8 km/s |
| 40 km/s | Too fast |
| 50 km/s | Much too fast |
The Earth moves round the Sun in its orbit at a mean velocity of about 30 km/s.
Answer: (b) 30 km/s.
Why each option is right or wrong
- (a) Incorrect. 20 km/s is well below Earth's orbital speed.
- (b) CORRECT. Earth's mean orbital velocity is about 30 km/s (29.8 km/s).
- (c) Incorrect. 40 km/s overstates the orbital speed.
- (d) Incorrect. 50 km/s greatly overstates the orbital speed.
Key point
The Earth moves round the Sun at an average speed of about 30 km/s.
Remember
Earth's mean orbital velocity: about 30 km/s.
Common mistakes
- Confusing orbital speed with Earth's rotational speed at the Equator (about 0.46 km/s).
- Forgetting the speed varies slightly between perihelion and aphelion.
- Mixing the speed in km/s with km/h.
Exam tip
Orbit speed about 30 km/s, roughly 1,08,000 km/h.
Sources
- NCERT Class VIII Science — Stars and the Solar System
- NASA — Earth Fact Sheet (Goddard Space Flight Center, Planetary Fact Sheets)