The Milky Way arcs high overhead this evening. It forms a hazy, glowing band of light, like a subtle cloud. It's the combined glow of millions of stars in the disk of the Milky Way galaxy. But it's visible only from dark viewing locations, far from city lights.
Folded within the Milky Way are a few dark blobs. There are plenty of stars in those regions of the sky. But the dark blobs are clouds of cold gas and dust -- the raw materials for future stars and planets.
The clouds are darkened by the dust -- tiny grains of material that are a lot like the dust you find on your bookshelves. In fact, some of that dust does come from beyond Earth; more about that tomorrow.
Some of these dust grains were actually born inside stars.
As a star nears the end of its life, it produces carbon, oxygen, and other elements deep in its core. Currents like those in a pot of boiling water dredge some of these atoms to the star's surface. In some stars, the individual atoms combine to make solid grains, which are pushed into space by the stars' radiation. In other stars, the grains don't form until the atoms are already out in space. Either way, as they cool, they link up with other grains, forming larger particles.
Over time, these particles scatter into space. Some of them form parts of large, dark clouds -- like those that speckle the Milky Way. The clouds may collapse to give birth to new stars and planets -- planets that are made in part from grains of cosmic dust.
Script by Damond Benningfield, Copyright 2008
For more skywatching tips, astronomy news, and much more, read StarDate magazine.