Have you ever walked into a theater after the movie has started? Although you know it is filled with seats and other people, you really can't see anything but a big, bright, moving screen! Telescopes have revealed that the universe is filled with endless luminous galaxies, but most astronomers believe that the galaxies are surrounded by a dark halo or circle filled with dark matter. How did they discover the existence of this substance? Numerous calculations seem to prove there is too much gravity beyond the edge of each galaxy and throughout the universe for the amount of bodies of light that we are able to see! Scientists have come to question their original beliefs that all objects with gravitational pull must be visible. At this point in time astronomers can only guess what form this unseen matter might take. It might be dark galaxies, dwarf stars too faint to be seen, or black holes. Most scientists believe the dark matter formed right after the big bang and that it could be particles that are so tiny that they can't be seen or aren't able to send out enough radiation to be measured! Sounds hard to believe, doesn't it? Even after they have totaled up all the light and dark matter, there is still 70 percent of the gravity they can't explain in the universe. They believe that dark energy, the driving force for the expanding universe, accounts for the rest of it. One way to think of it is like magnetism or electricity. Just because you can't see it doesn't mean it isn't there. Until astronomers discover a way to measure it, they just have to believe it is there because they see its effect!

Name That Nebula

Over 200 years ago, astronomer Charles Messier was searching for comets. Instead, he found lots of fuzzy objects that looked like comets but were really star clusters, galaxies, and nebulae. Messier described these objects and their positions using numbers, but modern astronomers have given these deep sky objects more descriptive names! Figure out the picture puzzles to learn the names of nine of the nebulae on Messier's list.