The Scintillation of Stars

Abstract

IT is usual to advance a physical explanation of the scintillation of stars. Thus Wood¹ suggests that gradations in the refractive index of the atmosphere give rise to striæ. The gradations are said to be due to hot and cold currents which act as convex and concave cylindrical lenses. Wood also thinks that the disappearance of the effect when a given star is viewed through a telescope is due to the objective collecting several such striæ (which are 3–4 cm. apart), the average illumination being constant. Recently, however, a physiological explanation has been advanced (Hartridge²) ; both change of brightness and colour are ascribed to the slight movement of the star image over the retina and also to local variations in the retinal receptors, which will be more sensitive in some parts and less so in others ; where red receptors abound there will be a bias in favour of red, whereas other regions will be more favourable to green, for example. It seems likely that Holmgren³ was the first to observe variations in hue in a local source of light. He found that a monochromatic yellow light was sometimes seen red, sometimes green, and sometimes colourless. Blue was found to appear green, blue, violet or colourless.