Question

A star is seen to be rising on the eastern horizon at 23:00 hrs. At what time will the same star rise 20 days later?

a. 22:00 hrs
b. 23:00 hrs
c. 00:00 hrs
d. 01:00 hrs

Answer 1

Using the principle of sidereal time, a star that rises at 23:00 hrs on the eastern horizon will rise approximately 80 minutes earlier, or around 21:40 hrs, after 20 days.

Step-by-step explanation:

The question is about the sidereal time and the rising time of stars. Understanding sidereal time is important in astronomy because it is based on Earth's rotation relative to distant stars, resulting in a star rising approximately 4 minutes earlier each day. This knowledge allows us to calculate the rising time of stars on any given future date.

Given that a star rises at 23:00 hrs on the eastern horizon, it will rise 4 minutes earlier each successive day. Over the course of 20 days, this adds up to 80 minutes earlier. Therefore, if the star originally rises at 23:00 hrs, after 20 days it will rise around 21:40 hrs, which is approximately 22:00 hrs or option (a).