Image List

By studying two regions of maser activity in the spiral galaxy M33, astronomers have measured the slowest ever motion across the plane of the sky. Although its speed through space is large, M33 is so distant that it appears to move at the glacial pace of only 30 micro-arcseconds per year, 100 times slower than a snail on Mars as seen from Earth. Arrows indicate the predicted motions of the masers due to the galaxy's rotation.