Twinkle, twinkle, little star. How I wonder what you are. Well, wonder no more! Stars are large balls of extremely hot gas or, more accurately, hot gas and a gas-like substance called plasma. They are primarily composed of the two most common elements in the universe: hydrogen and helium. The "twinkle" comes from turbulence, or movement, in our atmosphere. It's similar to watching an object from the bottom of the swimming pool; the ripples and movement of the water distort what you see on land. In space, outside of our atmosphere, the stars don't twinkle.
Stars form within clouds of gas, dust, and debris, known as molecular clouds. Read more about the conditions for star formation on our nebulae page. Over the course of billions of years, they pass through several phases and eventually die. (Image Right: White dwarf stars (NASA and H. Richer (University of British Columbia), Courtesy of NASA)
