Moon and Giants

Moon and Giants

Giants flank the Moon tonight. They’re among the brightest stars in the night sky, so you can’t miss them, even from a light-polluted city.

As night falls, look to the lower right of the Moon for Aldebaran, the eye of Taurus, the bull. Then look about twice that far to the upper left of the Moon for Capella. It’s the brightest star of Auriga, the charioteer, and the sixth-brightest star in all the night sky.

Aldebaran is a single giant. It’s more than 40 times the diameter of the Sun. It’s also a bit more massive than the Sun. It’s 65 light-years away.

Capella includes two giants. The system is closer than Aldebaran, at just 43 light-years. Both of the giants are about two-and-a-half times the mass of the Sun, and roughly 10 times the Sun’s diameter.

A star becomes a giant when it uses up the original hydrogen fuel in its core. The core shrinks and gets hotter, starting a new round of nuclear reactions. The hotter core pushes outward on the star’s outer layers. That causes the star to puff up to many times its original size, making it much brighter. Aldebaran, for example, is more than 400 times the Sun’s total brightness, while each of Capella’s giants is about 75 times the Sun’s brightness.

Eventually, each star will cast its outer layers into space, leaving only its small, hot core.

The Sun faces the same fate — beginning in several billion years.

More about the future of the Sun tomorrow.

Script by Damond Benningfield

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