Photo Agency - Astronomy - Space - Nature

> Southern Cross and pointers - Star trails

Southern Cross and pointers - Star trails

author: David Malin Images/Novapix

reference: a-pas01-10051

Image Size 300 DPI: 25 * 25 cm

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.

Keywords for this photo:

1985 - ALPHA CENTAURI - ASTRONOMY - COLOR - CONSTELLATION - CRUX - NIGHT - SOUTHERN CROSS - SOUTHERN HEMISPHERE - STAR - STAR TRAILS - STARRY SKY -