Stars like the Sun go through several distinct phases of life, from embryo to corpse.

Consider Aldebaran, the bright eye of Taurus, which accompanies the Moon tonight. It’s more than six billion years old – older than the Sun. And it’s well into “old age.”

Aldebaran was born when a cloud of gas and dust collapsed. For millions of years, it shined as a result of the heat generated by that collapse – its “embryonic” phase. Eventually, its core got hot enough to ignite the fires of nuclear fusion, and Aldebaran entered the prime phase of life – fusing hydrogen to make helium.

A few hundred million years ago, it used up the hydrogen in the core. The core got smaller and hotter, and Aldebaran began fusing the hydrogen in a shell around the core. At the same time, its outer layers puffed up, so Aldebaran is more than 40 times wider than the Sun. This is the giant phase of life.

Eventually, the core will get hot enough to fuse the helium to make carbon and oxygen. But when the helium is gone, fusion will stop. The core will get smaller and hotter, and its radiation will push the star’s outer layers into space. Only the hot, dead core will remain – a white dwarf.

Even that isn’t the end, though. The white dwarf will cool and fade. Hundreds of billions of years from now – and perhaps much longer – it’ll stop producing any visible light at all. That will make it a black dwarf – the final stage for the eye of the bull.

Script by Damond Benningfield