UPSC Prelims 2008 Q44: Geography – Astronomy & Earth - Sun System
Consider the following statements:
1. The albedo of an object determines its visual brightness when viewed with reflected light.
2. The albedo of Mercury is much greater than the albedo of the Earth.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (a) 1 only
Explanation
Checking two claims about albedo
Albedo measures how much light a surface reflects, with specific implications for celestial bodies' brightness.
| Statement | Verdict | Reason |
|---|---|---|
| 1. Albedo determines visual brightness via reflected light | Correct | Albedo is precisely the measure of how much incoming light a surface reflects, directly determining its visual brightness when viewed in reflected light |
| 2. Mercury's albedo is much greater than Earth's | Incorrect | Mercury actually has a much LOWER albedo than Earth (Mercury is dark and rocky, reflecting less light, while Earth's clouds/oceans/ice reflect more) |
Correcting the second claim:
| Point | Correct detail |
|---|---|
| Mercury's albedo | Lower than Earth's (NOT greater) |
| Earth's albedo | Higher, due to clouds, oceans, and ice |
Answer: (a) 1 only.
Why each option is right or wrong
- (a) CORRECT. The definition of albedo (statement 1) is accurate; Mercury's albedo is actually lower, not greater, than Earth's.
- (b) Incorrect. Statement 2's 'Mercury greater than Earth' claim is reversed, so '2 only' is wrong.
- (c) Incorrect. Statement 2 is inaccurate, so 'both' cannot be correct.
- (d) Incorrect. Statement 1 is accurate, so 'neither' is wrong.
Key point
Albedo does determine visual brightness via reflected light (statement 1, correct) — but Mercury's albedo is actually LOWER than Earth's, not greater as statement 2 claims, since Mercury's dark rocky surface reflects less light than Earth's clouds/oceans/ice.
Remember
Albedo determines visual brightness via reflected light — but Mercury's albedo is actually LOWER than Earth's, not greater.
Common mistakes
- Reversing Mercury and Earth's relative albedo values.
- Not understanding that cloud cover, oceans, and ice significantly boost Earth's reflectivity compared to a dark, airless planet like Mercury.
- Confusing albedo's definition (which is accurate in statement 1) with the specific planetary comparison (which is wrong in statement 2).
Exam tip
Mercury (dark, rocky) has LOWER albedo than Earth (clouds, oceans, ice reflect more light). A common reversed-comparison trap.
Sources
- Encyclopaedia Britannica — albedo
- NCERT Class XI Geography — Fundamentals of Physical Geography — Solar Radiation, Heat Balance and Temperature