Stellar Motion:

Stars are not fixed  in  the heavens. They are moving within  the galaxies. The speed of a star moving toward or away from the Earth is indicated by a shift of  its spectral lines. If a star is approaching  the Earth, its lines shift towards the blue end of  the spectrum. If  it is moving away from the Earth, its lines shift towards the red end of the spectrum. The greater the star's speed, the more its lines shift. You have read that there are many kinds of stars-blue, yellow or red, normal or giant, pulsating or releasing excessive energy. Most stars nlove together in groups. Only one out of four stars may  travel alone. Of  the rest, almost a third are double stars and the rest are groups of many stars. In a double star system, known as a binary, two stars orbit one another.  In a triple system; there are three stars-all  three may move around each other, or two of  them may move around the third. Then there are loose clusters, with a few dozen stars, to the large globular clusters containing hundreds of  thousands of  stars, all moving in many possible ways.