Answer to Question #87191 in Astronomy | Astrophysics for Amit

Question

Explain why sidereal day is shorter than the solar day. What is the magnitude of this difference? What effect does this have on the rising of stars in the evening?

Answer 1

Explain why sidereal day is shorter than the solar day.

Solution:

The solar day is the time it takes for the Sun to appear in the same meridian in the sky. The sidereal day is the time it takes for a distant star to appear in the same meridian in the sky. 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 into the same apparent meridian in the sky.

What is the magnitude of this difference?

Solution:

Sidereal day is 23 hours, 56 minutes and 4.1 seconds by definition. Our usual definition of an Earth day is 24 hours. In this way, the sidereal day is 4 minutes and 4.1 seconds faster.

What effect does this have on the rising of stars in the evening?

Solution:

This means that a particular star will rise 4 minutes earlier every night, and is the reason why different constellations are only visible at specific times of the year.