Astronomy Picture of the Day

Explanation: What can 100,000 galaxies tell you? Perhaps the structure and composition of the universe. Astronomers using the Two Degree Field (2dF) spectrograph on the Anglo-Australian Telescope (AAT) in Australia have now measured the redshifts of over 100,000 galaxies in a thin ribbon of the sky. The results show how galaxies are scattered in the universe out to 4 billion light years. Huge clusters, long filaments, and empty voids measuring over 100 million light years across are visible in the resulting 2dF map, pictured above. The map is interesting not only for what it shows but also for what it does not show. It does not show even larger structures that would be expected were the universe filled to critical density with normal matter. These results do not contradict recent evidence that most of the universe is made of some type of unusual dark energy, however.