By Ron Cowen
Viewing galaxies so distant that the light now reaching Earth reveals what they looked like billions of years ago isn’t the only way to learn about how galaxies form. Astronomers can examine a much closer specimen–our own Milky Way.
In contrast to previous Milky Way projects, which measured the motions of some 2.5 million stars as they march across the sky, a survey that began in April will track the movement of stars toward or away from Earth. By measuring this component of motion, which is currently known for only 20,000 stars, astronomers plan to reconstruct more details about how the Milky Way formed.