Coloured Lamps? ~ No, an almost white star. Images by Rob Kaufman in Victoria, Australia.  ©Rob Kaufman, shown with permission.

"The composite is of the bright star Sirius, caught at low altitude [9° above the horizon] in poor atmospheric 'seeing' (turbulence) after a very hot day. The sequence is 30 consecutive frames taken with a webcam at 30 frames per second, so this represents 1 second of elapsed time. The webcam was slightly defocused to avoid burn-out and bring out the colours. Celestron NexImage webcam through 4.5" f8 reflector and 2x Barlow."

Poor seeing, the bane of astronomers, is caused by the starlight passing through uneven and moving layers of air at different temperatures and therefore densities.

The unsteady layers behave like shifting prisms and lenses, refracting the starlight one way and then another. Whenever refraction occurs the light is dispersed into its component colours.


About - Submit Optics Picture of the Day Galleries Previous Next Today Subscribe to Features on RSS Feed