Astronomers measure slowest motion across the sky

“A snail crawling on Mars would appear to be moving across the surface more than 100 times faster than the motion we measured for this galaxy,” said Mark Reid of the Harvard-Smithsonian Center for Astrophysics, a co-author on the paper. Reid and his colleagues used the National Science Foundation’s Very Long Baseline Array (VLBA) to measure the motion across the sky of a galaxy located nearly 2.4 million light-years from Earth. While scientists have been measuring the motion of galaxies directly toward or away from Earth for decades, this is the first time that the transverse motion (called proper motion by astronomers) has been measured for a galaxy that is not a nearby satellite of the Milky Way.