Aldebaran is like a reverse time capsule. Instead of preserving mementos from the past, the star shows us what we can expect in the distant future – the far, far distant future. It’s in a phase of life that the Sun will pass through in several billion years.

Aldebaran marks the eye of Taurus, the bull. It’s low in the western sky as evening twilight fades. It’s a little to the left of Venus, the brilliant “evening star.”

The Sun is in the prime phase of life. It’s steadily “fusing” the hydrogen atoms in its core to make helium. That produces the energy that makes our star shine.

Aldebaran has already completed that phase. Its core has converted the hydrogen to helium. Now, the star is fusing the hydrogen in a thin layer around the core. This layer is especially hot. Its radiation pushes outward on the surrounding layers of gas. That’s caused Aldebaran to swell to about 45 times the Sun’s diameter. And that’s made the star more than 400 times brighter than the Sun.

Over many millions of years, Aldebaran will use up that shell of hydrogen. Nuclear fusion will then fire up in the helium core, briefly making the star even bigger and brighter. After that, fusion in the core will begin to shut down. Aldebaran’s outer layers will blow away, briefly forming a colorful bubble. As the bubble dissipates, only the star’s now-dead core will remain – a final memento of a once impressive star.

Script by Damond Benningfield