138 The Ottawa Naturalist. [Oct: 



"Twinkle, twinkle little star, how I wonder — what makes 

 you twinkle?" 



The twinkling or scintillation of the stars has been noticed 

 and noted from ancient times. Aristotle remarks that "the 

 stars twinkle, but the planets do not." Although planets do not 

 scintillate, or do not scintillate as much as stars, yet their twink- 

 ling has often been observed. Associated with the scintillation, 

 the sparkling "like a diamond in the sky" is often seen, but this 

 rapid change of color is confined to low altitudes, that is, when 

 the star is not high above the horizon. What seems somewhat 

 puzzling is the fact that when a twinkling star is viewed through 

 a telescope the scintillation ceases, and instead one sees a little 

 disk with ill-defined edge. The phenomenon of twinkling is due 

 to refraction or bending of the rays of light coming through our 

 atmosphere. When the air is "unsteady," this bending becomes 

 unsteady too, with the result that the rays of light from a star 

 are "trembling" and flit to and fro across the pupil of the eye, 

 and make the star twinkle. As a telescope has a very big eye, 

 the object glass, and although the trembling ravs fall upon it, it 

 gathers so many that when viewed at the eye-end, the twinkling 

 has apparently ceased, but it makes itself apparent by the little 

 disk of light mentioned above, for it must be remembered that 

 the stars are mere points of light and the most powerful telescope 

 reveals no disk. From this it is obvious why the moon does not 

 scintillate, it has a surface that radiates light, and the individual 

 scintillations from points thereon are drowned, so to speak, in 

 the multitude. As to sparkling, or rapid change of colour, the 

 light, as we ordinarily see it, is white, in reality it is composed of 

 all the colours of the rainbow. These various colours do not tend 

 to the same degree, when passing through our atmosphere, some 

 bend more and some less. From any particular bundle of 

 (white )rays we would receive say only the red rays, from another 

 bundle only the blue and so on; so that collectively we would 

 have the impression of white light, i.e., of all colours combined. 

 This is generally the case when the successive layers of our 

 atmosphere are fairly homogeneous. When, however, this is not 

 the case, when irregular layers of varying densities traverse the 

 air, then the dispersion of the white rays into their constituent 

 colours becomes apparent to the eye, the blending of the colours, 

 or rather of the particular rays which give us the sensation of 

 colour, not taking place so continuously. Hence the star appears 

 momentarily of that colour which is represented by the particular 

 ray that meets the eye. When these irregular conditions prevail 

 in our atmosphere then sparkling besides twinkling of the stars 

 is possible. As these irregularities are mostly confined to the 



