This is a mark of achievement for a home composter, what is called "hot" compost. There really was steam rising from the pile this morning, and if you peel back the top layer, a blast of heat hits you in the face.
At this temperature, the pile should decompose fairly quickly. Mostly it is grass clippings recently collected from the lawn and an equal measure of shredded leaves saved from last fall. Thus, equal parts "green" and "brown." The heat comes from all those thermophilic bacteria in the pile, chomping away on the organic matter and multiplying like mad. They will continue to generate heat like this for a few days as long as there is an abundance of nitrogen (the "green") in the pile. Then activity will slow down and it will soon be time to turn the pile to stoke it with more oxygen.
Of course you don't have to compost this way. Things will break down if you just throw them in a heap and leave them alone. But that takes months longer and I like to know that I will have plenty of compost to work into my vegetable beds later in the season, when it comes time to planting our fall crops.
Ain't nature grand?