Here's a short description from the NASA glossary: Interstellar Dust Grains: Not the dust one finds around the house, which is typically fine bits of fabric, dirt, or dead skin cells. Rather interstellar dust grains are much smaller clumps, on the order of a fraction of a micron across, irregularly shaped, and composed of carbon and/or silicates. Dust is most evident by its absorption, causing large dark patches in regions of our Milky Way Galaxy and dark bands across other galaxies. The exact nature and origin of interstellar dust grains is unknown, but they are clearly associated with young stars. <br><br>-Ed.<br><br><blockquote class="blockquote"><div class="italic"><i>Charles Geiger said:</i><br><br>I must have missed something important...what is the space dust made of? Doesn't the dust have to be made of hydrogen or something more complex? </div></blockquote>