Binary Star
Here
is an imaginary landscape of a planet in orbit around a binary star. At
least a third of all the stars you see in the night sky are actually
binary, or double stars. Some are even triples, or quadruples, or more.
Hundreds of these multiple stars can be seen as such in small
telescopes. Many pairs show differences in brightness and color caused
by the differing masses and temperatures of the companions. A pair of
stars as close together as those in my image could not be resolved in a
telescope. It would be detected spectroscopically, with the spectra
showing two sets of absorption lines. Visual binaries are typically
separated by billions of miles.
Image copyright by Joe Bergeron.