Gamma Hydra

• ‹ Previous program
• 829 of 1971
• Next program ›

After a long and hectic life, a star in the constellation Hydra appears to be taking a break. The nuclear "engine" in its core is quiet. But it'll get busy again soon. And when it does, it'll pump up the star's outer layers like a giant balloon.

Gamma Hydra marks the tail of the water snake -- the longest constellation in the sky. The star climbs into view in the southeast by around 10 o'clock, and stands highest in the sky a few hours later.

Gamma Hydra is about 130 light-years away. The fact that it's visible to the unaided eye across such a great distance means that it's a good bit brighter than the Sun.

The star is so bright in part because it's nearing the end of its life, so it's puffed up a bit. It's "burned" through the hydrogen fuel in its core to make helium. The helium is basically just sitting there, so it's not producing any energy. Instead, the core is shrinking and getting hotter. Before long, it'll get hot enough to ignite the helium, which will begin fusing together to make heavier elements.

When that happens, radiation pressure from the core will puff up the star's outer layers, so Gamma Hydra will get much bigger -- big enough to hold a half million stars as big as the Sun. Then it'll cast those outer layers into space, leaving only its hot, tiny core -- the last remnant of a retired star.

The Sun itself will go through the same process as it reaches the end of its own life -- in several billion years.

Script by Damond Benningfield, Copyright 2010

For more skywatching tips, astronomy news, and much more, read StarDate magazine.