Scintillation of Capella

Various colours displayed by a twinkling Capella, the sixth brightest star in the night sky. This change in colour, or scintillation, is caused when starlight passes through turbulence in the atmosphere, which diffracts the light. This is usually caused by small fluctuations in air density due to temperature gradients, but also cloud cover and light pollution. The series of photos were taken at 400mm and with the star out of focus (to increase its apparent size and reduce brightness). Each photo was taken at a 1/4 second shutter speed, though a lower speed would have produce more vibrant colours, albeit in a darker exposure. I chose some of the more vibrant colours here to populate this composite image. I saw this produced for Sirius in the Insight Astronomy Photographer of the Year in 2016 and thought it would be interesting to try. I will have to give it another go when Sirius comes into view later this fall as it is much brighter than Capella.