Astronomy Picture of the Day

Explanation: What does the universe look like on small scales? On large scales? Humanity is discovering that the universe is a very different place on every proportion that has been explored. For example, so far as we know, every tiny proton is exactly the same, but every huge galaxy is different. On more familiar scales, a small glass table top to a human is a vast plane of strange smoothness to a dust mite -- possibly speckled with cell boulders. Not all scale lengths are well explored -- what happens to the smallest mist droplets you sneeze, for example, is a topic of active research -- and possibly useful to know to help stop the spread of disease. The featured interactive flash animation, a modern version of the classic video Powers of Ten, is a new window to many of the known scales of our universe. By moving the scroll bar across the bottom, you can explore a diversity of sizes, while clicking on different items will bring up descriptive information.