CHANGE OF COLOUR IN THE STARS.
The scintillation or twinkling of the stars is accompanied by variations of colour, which have been remarked from a very early age. M. Arago states, upon the authority of M. Babinet, that the name of Barakesch, given by the Arabians to Sirius, signifies the star of a thousand colours; and Tycho Brahe, Kepler, and others, attest to similar change of colour in twinkling. Even soon after the invention of the telescope, Simon Marius remarked that by removing the eye-piece of the telescope the images of the stars exhibited rapid fluctuations of brightness and colour. In 1814 Nicholson applied to the telescope a smart vibration, which caused the image of the star to be transformed into a curved line of light returning into itself, and diversified by several colours; each colour occupied about a third of the whole length of the curve, and by applying ten vibrations in a second, the light of Sirius in that time passed through thirty changes of colour. Hence the stars in general shine only by a portion of their light, the effect of twinkling being to diminish their brightness. This phenomenon M. Arago explains by the principle of the interference of light.
Ptolemy is said to have noted Sirius as a red star, though it is now white. Sirius twinkles with red and blue light, and Ptolemy’s eyes, like those of several other persons, may have been more sensitive to the red than to the blue rays.—Sir David Brewster’s More Worlds than One, p. 235.
Some of the double stars are of very different and dissimilar colours; and to the revolving planetary bodies which apparently circulate around them, a day lightened by a red light is succeeded by, not a night, but a day equally brilliant, though illuminated only by a green light.