Abstract
Binary stars, or, as they are sometimes called, double stars, are stars that may appear to the naked eye to be just one star, but on observation with either binoculars or telescopes resolve themselves into two stars. Indeed, some apparently single stars turn out to be several stars! Many appear as double stars due to their lying in the same line of sight as seen from Earth, and these are called optical doubles. It may well be that the two stars are separated in space by a vast distance.
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Notes
- 1.
For a very detailed listing of beautiful double and multiple stars, see Field Guide to Deep Sky Objects 2nd Edition by the author.
- 2.
Regardless of whether the binary star system is a visual, spectroscopic, eclipsing or astrometric binary star system.
- 3.
There are literally thousands of double, triple, and multiple star systems in the sky, all within reach of the amateur astronomer. The list that follows is but a taste of what awaits the observer. If your favorite star is omitted, I apologize, but to include them all would have been impossible.
- 4.
Note that the position angle and separation are quoted for epoch 2000.0. With double stars that have small periods, these figures will change appreciably.
- 5.
Cepheid variables are covered in a later chapter.
- 6.
Yes, I know that this is a triple star system, but as it contains a white dwarf, I’ve included it in the list.
- 7.
The semi-major axis is a term used in elliptical orbits (as nearly all orbits are). It is defined as half of the longer axis of an ellipse, and it is the average separation of the two stars.
- 8.
It is this wobble that is used to detect unseen planets around stars!
- 9.
Note that a A  + a B add up to the semi-major axis a, as used in Kepler’s Law.
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Inglis, M. (2015). Binary Stars and Stellar Mass. In: Astrophysics Is Easy!. The Patrick Moore Practical Astronomy Series. Springer, Cham. https://doi.org/10.1007/978-3-319-11644-0_9
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DOI: https://doi.org/10.1007/978-3-319-11644-0_9
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