UPSC Prelims 2001 Q77: Geography – Astronomy & Earth - Sun System
If the stars are seen to rise perpendicular to the horizon by an observer, he is located on the
- (a) Equator
- (b) Tropic of Cancer
- (c) South Pole
- (d) North Pole
Answer: (a) Equator
Explanation
Where stars are seen to rise perpendicular to the horizon
| Observer's place | How the stars rise |
|---|---|
| Equator | Straight up, at 90° to the horizon — the celestial poles lie on the horizon |
| Tropic of Cancer (23.5° N) | At a slant of 66.5° to the horizon |
| North Pole | Stars do not rise or set; they circle parallel to the horizon |
| South Pole | Same as the North Pole — circles parallel to the horizon |
Stars appear to move along circles parallel to the celestial equator. At the Equator the celestial equator passes straight overhead and meets the horizon at a right angle, so stars rise perpendicular to the horizon. At the poles, stars only circle parallel to the horizon.
Answer: (a) Equator.
Why each option is right or wrong
- (a) CORRECT. At the Equator stars rise vertically.
- (b) Incorrect. At the Tropic of Cancer stars rise at a slant.
- (c) Incorrect. At the South Pole stars circle parallel to the horizon.
- (d) Incorrect. At the North Pole stars circle parallel to the horizon.
Key point
The angle at which stars rise = 90° minus the observer's latitude.
Remember
Stars rise vertically at the Equator; circle flat at the poles.
Common mistakes
- Choosing a pole because stars there seem 'straight above'.
- Not knowing that stars never set at the poles.
- Mixing up the celestial equator and the horizon.
Exam tip
Angle of rising = 90° − latitude; at latitude 0° that is 90°.
Sources
- NCERT Class VIII — Science, chapter 'Stars and the Solar System'
- G. C. Leong — Certificate Physical and Human Geography, chapter 'The Earth and the Universe'