Stellar Factory 
Cassiopeia, the queen, is written large across the northern sky this evening. It looks like a big letter M or W. It's high in the northwest at nightfall, and wheels low across the north later on.
About three centuries ago as seen from Earth, one of Cassiopeia's stars exploded as a supernova. It blasted its outer layers into space at a few percent of the speed of light. This material continues to expand into space as a giant shell. It contains lots of oxygen and other elements that will disperse into the galaxy. These elements may someday be incorporated into new stars, planets, or even living organisms.
These elements were forged inside the star itself. Under the extreme temperatures and pressures in its core, lightweight elements "fuse" together to form heavier ones. The first step in this process fuses hydrogen to make helium -- the process that's taking place today in the Sun.
As stars age, they use up the hydrogen and start fusing the helium to make other elements. Stars like the Sun make carbon, nitrogen, and oxygen.
The heaviest stars make these elements, too. But the cores of these stars get much hotter, allowing them to make even heavier elements. And when they explode, they forge even more elements. So elements like iron, lead, uranium, and many others were manufactured in stars like the one that produced the supernova in Cassiopeia, then blasted into space in the stars' spectacular deaths.
Script by Damond Benningfield, Copyright 2010