Observing Double Stars by John A. Barra Having completed a series of five articles in the Primer for the Beginner series, I am beginning a new series aimed at those persons who are now ready to use some of those astronomical techniques learned in the former series. The intermediate amateur astronomer will learn how to observe the various deep sky objects and gain a little understanding of the science involved. The emphasis, however, will remain on having fun while observing. The first subject will be observing double stars.
Some double stars are actually optical doubles.
They happen to almost be in the same line of sight, so they appear close together when they may be far apart in actual distance. Delta Herculis and Alpha Ceti are examples of such optical pairs. However, the vast majority of double or multiple star systems are stars that are gravitationally related. They are called binary stars. I will deal exclusively with visual binaries, pairs that can be separated with the use of optical aids.