What is wrong with my pine tree?

I have a pine tree in my front yard, I don't know what type it is though. I have just noticed that a large portion of the needles are turning yellow, not brown as if its not getting water. The needles are in little bunches that look like broom ends and there are several bunches on each branch. One bunch might be completely yellow, one completely green and one with more yellow than green in it. The yellowing seems to have started on the inside and is working its way outward. Can anyone tell me what this is? I have been searching the forestry page looking for an answer and so far nothing. Hope someone here can give me an idea of whats happening to my tree. Thanks!