AAO image reference MISC 6. « Previous || Next »
Image and text © 1991-2002, Anglo-Australian Observatory, Photograph by David Malin.
The best nights for most professional astronomy projects are 'photometric', nights, where the light from a bright star -- any star -- remains constant for hours at a time. Long experience shows that any visible cloud will diminish the quality of the data obtained, even if it is not near the line of sight to the object of interest. However, these same clouds can give pictures taken for non-scientific purposes an unexpectedly abstract, unworldly quality. The picture here was made on one such partially cloudy night at Siding Spring. In the foreground are the distinctive shapes of the Warrumbungle mountains in outback New South Wales.
The exposure, on 400 ISO transparency film, was begun at the end of astronomical twilight, when the sun has descended 18 degrees below the horizon. There was a crescent moon and cloud around the south-western horizon. Even a small amount of moon increases the sky brightness, so the lens aperture was reduced to F/8, two stops down from the setting used for a truly dark night. Even so the clouds are visible against the sky. The exposure continued for several hours after the moon had set, and breaks in the star trails reveal that cloud had come and gone during the night. More information on star trail photography is here.
Related images
AAT 5. Star trails southwest of the AAT dome
AAT 6. Star trails around the south celestial pole
MISC 18. The view to the north from Siding Spring
MISC 5. Dawn and evening twilights reflected in the AAT dome
MISC 8. Aurora Australis from Siding Spring
MISC 12. Orion's belt rising over the lights of Coonabarabran
MISC 14. South celestial pole star trails
MISC 13. North celestial pole star trails
MISC 15. North and South celestial poles star trails
MISC 11. Orion star colours, step-focus technique
MISC 22 The AAT dome from the Director's Cottage.
MISC 16. Southern Cross and Pointers, star colours - step-focus technique, long trails
MISC 23 Southern Cross and Pointers, star colours - step-focus technique, short trails
MISC 19. Sunset 'star' trail, the track of the setting sun