Fig. 413.
350. Physically Double and Multiple Stars.—In the majority of cases the components of double and multiple stars are in reality comparatively near together, and are bound together by gravity into a physical system. Such combinations are called physically double and multiple stars. The components of these systems all revolve around their common centre of gravity. In many instances their orbits and periods of revolution have been ascertained by observation and calculation. Fig. 415 shows the orbit of one of the components of a double star in the constellation Hercules.
Fig. 414.
351. Colors of Double and Multiple Stars.—The components of double and multiple stars are often highly colored, and frequently the components of the same system are of different colors. Sometimes one star of a binary system is white, and the other red; and sometimes a white star is combined with a blue one. Other colors found in combination in these systems are red and blue, orange and green, blue and green, yellow and blue, yellow and red, etc.
Fig. 415.
If these double and multiple stars are accompanied by planets, these planets will sometimes have two or more suns in the sky at once. On alternate days they may have suns of different colors, and perhaps on the same day two suns of different colors. The effect of these changing colored lights on the landscape must be very remarkable.