Here’s a deceptively simple question we recently got at Perkins Observatory: Do the stars move?Not too long ago, asking such questions got you burned at the stake. These days I can give the answer in the newspaper. Yes, they move, but not in the way you might think. Much of the motion we see is illusory.
Our Milky Way galaxy is often described as a flattened disk of hundreds of billions stars. That description leaves out some of our galaxy’s most interesting parts. Hovering above and below the main disk are the suburbs of our galactic city — 150 or so globular clusters of stars. Along with some stray stars and occasional gas molecules, globular clusters are the main constituents of what is more properly called the “galactic halo.”
The Milky Way, our galaxy, is one of hundreds of billions (or trillions — who knows?) of tiny islands of stars sprinkled throughout the vast cosmic ocean of space. Seen from the top, galaxies are often shaped like flat spirals — children’s pinwheels of uncountable stars. Seen from the side, galaxies look much like lenses bulging at the center and tapering to points at the edges. Most of a galaxy’s stars are spread throughout the lens-like structure, the galaxy proper.