Daytime and Nighttime Stars:
I just google searched to see some information about any possible difference between Daytime and Nighttime sky but first few pages however could not satisfy my query. So here I am writing down my understanding of the issue. First of all there must be stars in Daytime. Secondly, those stars must be different from those what we observe in Night Sky.
Why there must be stars in Day Sky?
Well, I never have seen. I read somewhere that stars are visible in daytime from deep vertical coal mines. I also heard/read that stars become apparent during complete solar eclipse etc. Apart from these reasons, sun is also a star and is visible in daytime.
Why Nighttime stars should be different from those what we observe in Night Sky?
As we cannot see The Sun in the night sky, so we should not be able to see other objects of Day Sky at Nighttime. The Sun is above of us at Daytime but it is beneath of us in Nighttime. So other Daytime fixed objects (stars) also should be beneath of us at Nighttime.
At Night, we see those things which were beneath of us at Daytime. This is very simple position. I do not know the official position of Science on this issue. I may be wrong but this is what I can understand at my own.
Update on April 27, 2011:
Last night I observed apparent movement of ‘fixed stars’ in sky. Today I google searched to see details of movements of stars. What I learn is that stars, just like sun, also rise in east and set in the west.
Following web page discusses this thing:
So if Stars also change positions like sun, then obviously daytime stars are different from nighttime stars.