Big Galaxy

StarDate: September 5, 2010

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A thousand years ago, people thought that Earth was special -- that it was the center of the universe. Today, we're told just the opposite -- that there's nothing special about our place in space.

But that's not true either. Our galaxy, the Milky Way, is indeed a special place. If it weren't, life would never have arisen here.

The Milky Way is much bigger, brighter, and more massive than most other galaxies. It's as bright as 15 billion Suns, and as heavy as a trillion of them. It's so big and heavy that many smaller galaxies orbit it.

Further perspective on the Milky Way's immense size comes when we look at the Local Group, the small cluster of galaxies to which the Milky Way belongs. It includes several dozen known galaxies, but only one of them -- the Andromeda galaxy, which is two-and-a-half million light-years away -- is thought to be larger. And even then, the Milky Way is thought to outweigh Andromeda.

Huge galaxies like the Milky Way are essential for the development of life. Only big galaxies have enough gravity to retain vital, life-giving elements such as oxygen and phosphorus that exploding stars shoot into space. These elements get recycled into new generations of stars and planets -- including our own.

If you have nice, dark skies, look for our life-giving Milky Way arcing high across the sky tonight. The subtle glow of its myriad stars arcs high across the east as darkness falls, and directly overhead later on.

 

Script by Ken Croswell, Copyright 2010

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

The one constant in the Universe: StarDate magazine

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