God made two great lights, one to govern the day and also one for the night, he also made stars. Is there a particular reason the sun and stars are separated?
To a pre-scientific people living in the bronze age, looking up at the sky one will note that the giant light that illuminates the daytime is a very different sort of thing than the tiny twinkling lights that come out at night.
They had no way of knowing that the sun was a star, just one very close to us, because they didn't conceive of the cosmos in the same way we do since the days of Copernicus and Galileo.
Some of the ancient Greeks, notably Anaxagoras (451 BC) and Aristarchus of Samos put forward the idea that the sun was a star up close, but it never caught on in the ancient world, and wasn't until much later that
a) The earth orbited the sun, not the other way around.
and
b) The sun was a star, but that it was our
star.
Both caught on.
More info here:
http://solar-center.stanford.edu/FAQ/Qsunasstar.html
It would be unfair to expect pre-scientific ancients, such as the author(s) of Genesis to know about such things. And thus for them the stars and the sun were very different sorts of heavenly bodies. Indeed the ancients also understood the known planets (Mercury, Venus, Mars, Jupiter, and Saturn) to be themselves
stars. This is why Venus in particular has been known as the "morning star" or the "evening star", these were peculiar sorts of stars though, they wandered (the Greek word from which we get "planet" means "wanderer") while "normal stars" were stationary.
Scripture isn't a science text book, and so we shouldn't expect it to act like one.
-CryptoLutheran