Question

A student claims that because of atmospheric refraction, the sun can be seen after it has set, and the day is, therefore, longer than if the earth had no atmosphere.

1. What does the student mean by saying that the sun can be seen after it has set?
2. Do you think that the students’ conclusion is correct?

Answer 1

1. The refraction of sunlight by the earth’s atmosphere causes the sun to be seen for about two minutes even after it has set below the horizon.
2. Yes, the student’s conclusion about the longer duration of the day because of atmospheric refraction is correct. Atmospheric refraction causes the sun to appear two minutes before the actual sunrise and two minutes after sunset. Therefore, the time from sunrise to sunset is increased by about four minutes. Thus, the day gets longer by about four minutes than if the earth had no atmosphere.