Most stars are grouped into small clusters of two or three stars each. Binary stars are two stars grouped together that appear to be one star. There are two kinds of binary stars visual and spectroscopic. Visual binaries are two stars that, when observed with a telescope, actually look like two stars. They revolve around each other very slowly.
Spectroscopic binaries are two stars that seem to be one.
They revolve around each other quickly. The only way to discern that there are two stars is with a spectroscope, which uses radiation to identify certain colors in the stars' spectrum. Multiple star systems or globular clusters can have anywhere from three stars to millions of stars grouped together. It is only possible to see the separate stars using a powerful telescope. Even though they seem to move through the sky at night, constellations are in reality standing still.