Question

If there were no atmosphere then the duration of day on the earth will ?

Answer 1

The absence of an atmosphere will affect the days on Earth in three ways.

In the absence of an atmosphere, the days will be darker than today's nights! Because physics!

The matter particles in our atmosphere scatter the light coming from the sun. Because of this scattered light, the atmosphere appears blue.

Answer 2

Due to refraction of sun's light our day is 2 min early and 2 min late. That refraction is due to atmosphere of earth if there would no atmosphere this thing would not happen and day would reduce to 24 hours minus 4 min.