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Q3 (CDS-I/2015) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Astronomy and astrophysics Answer Verified

Statement I: Sideral day is shorter than Solar day. Statement II: The motion of the Earth in its orbit around the Sun is termed as revolution.

Result
Your answer: —  Â·  Correct: A
Explanation

Statement I is true as a sidereal day (approximately 23 hours 56 minutes) is shorter than a solar day (24 hours). Statement II is also true, defining revolution as the Earth's motion in its orbit around the Sun [2]. Statement II provides the correct explanation for Statement I because the difference in day lengths is a direct consequence of Earth's orbital motion. As Earth rotates on its axis, it simultaneously revolves around the Sun [1]. To return the Sun to the same meridian (a solar day), Earth must rotate approximately 361° to compensate for the ~1° it moved along its orbit during that time. Conversely, a sidereal day only requires a 360° rotation relative to distant stars, making it about 4 minutes shorter than the solar day.

Sources

  1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 19: The Motions of The Earth and Their Effects > 19.2. Revolution of Earth > p. 252
  2. [2] Certificate Physical and Human Geography , GC Leong (Oxford University press 3rd ed.) > Chapter 2: The Earth's Crust > The Earth's Revolution > p. 6
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