Question

As you watch a star, you see it move 15 degrees across the sky. How long have you been watching it?

a. 1 hour
b. 3 hours
c. 15 minutes
d. 1 minute
e. 15 seconds

Answer 1

Watching a star move 15 degrees across the sky would take about 1 hour, due to the Earth's rotation making stars appear to move 15 degrees each hour.

Step-by-step explanation:

The movement of a star across the sky is a concept that relates to how the Earth rotates on its axis. As Earth rotates, it makes the stars appear to move across the sky. If we consider the sidereal day, which is the time it takes for the Earth to rotate once relative to the background stars (about 23 hours and 56 minutes), and that the stars appear to move 15 degrees in one hour (as the full circle is 360 degrees), then observing a star move 15 degrees would take approximately 1 hour. Therefore, if you have been observing a star as it moved across the sky by 15 degrees, you have been watching it for about 1 hour.