There is a big distinction to be made when it comes to night sky photography, which is whether or not you plan on photographing the stars in the night sky. If you do not plan on including stars in your shots, things are a lot simpler for you. That is true in a lot of ways, in that you dont need to worry as much about the clouds and weather, the impact of the moon, or light pollution.
When it comes to lens selection, it means that you can pretty much use whatever lens you want... more