Stars - The Southern Cross - Alpha and Beta of Centaur - Southern Cross and...

Stars - The Southern Cross - Alpha and Beta of Centaur - Southern Cross and pointers - Star trails - Because of the Earth's rotation, leaving the camera open, the stars advance towards the background of the sky. During the installation, gradually changing the focal length of the lens, the stars spread out and reveal their true color. Here it is the constellation of the Southern Cross (center right) and the Centaurus Alpha and Beta stars, in the center below, that are photographed in this way during a 30-minute pose. Star images are point sources of light of widely varying intensity. Normally, no single photographic exposure on colour film can capture their subtle colours. Those stars whose intensity is just right for their colour to be recorded appear insignificant on the photograph, while anything brighter is overexposed and washed out. By changing the focus of the lens during a star trail exposure, star images are spread out over the film surface. This effectively changes the amount of light in each star image as well as making it bigger. If this is done in a series of steps, as here, sooner or later all the star images will be recorded with an exposure that will reveal the star colours. Here we see the stars of the Southern Cross and pointers (alpha and beta Cen) recorded in an exposure of about 30 minutes, during which the lens focus was moved from infinity to about 1m in about 15 equally spaced steps