Question

What is the relationship between solar day and sidereal day?

• A. Solar day is shorter than sideral day
• B. Solar day is longer than sideral day
• C. Both are equal
• D. There is no relationship between the two

Answer 1

Answer: (B)

Solar day is longer than sideral day

Solar day is time taken for the Sun to appear on the same meridian in the sky. Sidereal day refers to time taken for a distant star to appear in the same meridian in the sky, which is in fact equal to time taken for the earth to rotate around its own axis as the angular speed is measured by taking distant stars as references.

Earth moves a little less than a degree around the Sun during the time it takes for 1 full axial rotation. So, for the Sun to appear on the same meridian in the sky again after 1 full axial rotation, the Earth has to rotate one extra degree to bring the Sun in to the same apparent meridian in the sky. This is why the solar day is longer than the sidereal day by about 4 minutes.