Julie Martin, age 9, of Omaha, Nebraska, for her question:

How can the stars burn without oxygen?

We know that a blazing wood fire must have oxygen to keep going. Even the flame of a candle needs oxygen to keep shining. But these are ordinary kinds of everyday fire. And the shining light of the blazing stars is something different. A star burns by nuclear fusion. This is what happens when an H-bomb goes off; only in a star it is a zillion times more so    and it goes on and on. Nuclear fusion is not at all like ordinary fire    and it doesn't need any oxygen to keep going.

One kind of atomic energy is called nuclear fission. The other kind is nuclear fusion. Fusion is fiercer than fission    but neither of them needs oxygen to keep going. This is why the stars can blaze away out there in space, where there is no oxygen. Our sun also is a star that burns by nuclear fusion. If it were a big coal fire and had plenty of oxygen, it would burn to ashes in 5,000 years. But its nuclear fusion furnace can last another ten billion years or so.