Dungbeetle,
The Israelites weren't any more enlightened about science than neighboring nations. Educated ancients knew the Earth was a sphere and even calculated its circumference.
The point is that of course God can do anything, but is there any evidence that this really happened? If he really wanted to make the Sun stand still (or stop the rotation of the Earth or create a secondary light, or use reflection techniques, etc.) he could do this with no problem. The problem is that the only record we have of this comes from the Bible. We have found that the Bible contains many myths and legends that cannot be verified and are so fantastic as to be pure bunk. Obviously such an event as this should show up in the contemporary records of neighboring nations as it must have been an amazing phenomenon. So far there are no other corroborating reports of this happening.
Thus we have an extraordinary claim (you would agree that the Sun standing still in the sky is extraordinary) with no extraordinary evidence (the record in the Bible is not very extraordinary since it is the only record of this event and there are many other false stories in the bible indicating the bible is an unreliable source for extraordinary claims). There is no reason to believe extraordinary claims without extraordinary evidence. Otherwise we would still believe in bogeymen under our beds.
rem
'A scientific opinion is one which there is some reason to believe is true; an unscientific opinion is one which is held for some reason other than its probable truth.' - Bertrand Russell