Sirius Twinkling
January 23, 2012
Photographer: David Lynch
Summary Author: David Lynch
Twinkling is the rapid fluctuation in brightness and color of a star. It’s caused by slight changes in density of air pockets called “seeing cells” that move across the observer’s line of sight. Air’s refractive index is determined, in part, by its density. Such undulations cause slight, momentary defocusing of the starlight resulting in brightness changes, also called scintillation. In extreme cases, the star’s position hops around. Twinkling also produces rapid color changes because air is slightly dispersive, i.e. the index of refraction varies slightly with wavelength.
Both brightness and color twinkling are shown here in a five-second exposure of Sirius using a telephoto lens that was wiggled slightly during the exposure. As the star‘s twinkling image skated around the focal plane, it traced out graceful, colorful arcs, fading in some places, brightening in others.
Here scintillation and telescope jitter, the bane of astronomers everywhere, have been recast into a stunningly beautiful image. Image taken on January 4, 2012.
