Why do so many countries have a crescent on their flags?

Question

I know there's some sort of religious significance but I don't know exactly what.

Answer 1

because it's cool

Answer 2

It's to the Muslims what the cross is to Christians, though different origins of course.

Answer 3

It's a Muslim symbol like the cross is to Christians or the Star of David to Jews.

Answer 4

The crescent moon is the symbol of Islam, but even before that it was the symbol of the Moon god, Sin, who was very popular in the Middle East thousands of years ago.  

Answer 5

Some flags feature a crescent shape. A crescent moon accompanied by a star often represents Islam

Answer 6

The star and crescent is considered an islamic symbol.

Check out: http://en.wikipedia.org/wiki/Star_and_cr...