The point in the orbital motion of a binary star system when the two stars are closest together is called the periastron; when they are furthest apart, it is known as the apastron.
Physical double stars are binaries, whereas optical doubles are not. A visual binary is one whose components can be resolved visually or photographically. An astrometric binary gives itself away by a regular wobble in the motion of a visible component. In a spectroscopic binary, the apparent separation is so small that the presence of two stars can only be deduced from regular changes in the Doppler shift of the stars' spectral lines. In a close binary the separation is comparable to the diameter of the stars.
The question of whether planets in a binary star system could conceivably support life has been widely discussed. See also habitable planets of binary stars.
Related category• TYPES OF STAR
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