It's the moon and the sun. I use a solunar table and they have proven to work for hunting and fishing.
http://shareware.pcmag.com/category....SiteID%5Dpcmag
The third program down is the one I use. It's free!
I also consider thweather in general. Like wind speed and direction. Sunny or overcast. Barometric pressure. YADAYADAYADA.
But when it comes right down to it you just got to hunt. Put the time in and don't worry about that stuff. It's interesting and may help once in a while, especially if you don't have a lot of time (You can look for the most active times in the coming week and pick your hunting days accordingly). But nothing beats being in the woods. You can't shoot them from your Lazyboy! LOL