The AAT dome by moonlight
AAO image reference MISC 4.     « Previous || Next »

The AAT by moonlight
Image and text © 1977-2002, Australian Astronomical Observatory, Photograph by David Malin.

It is unusual nowadays to find night-time location free of artificial light, so it is not surprising that we fail to notice that scenes viewed by moonlight are almost colourless. The human eye is insensitive to colour when light levels are low. By the light of the full moon we can see well enough to move around in unfamiliar terrain, but we cannot see its colour. To the eye, the trees, the grass and the sky above appear as shades of grey by moonlight, but our photograph reveals that the colours are still there. The most surprising is the blueness of the moonlit sky, which has never been described as blue throughout recorded history. It is blue for the same reason it is by day, because sunlight, reflected by the moon is scattered by the atoms and molecules of the earth's atmosphere.

The photograph was a 20 minute exposure on colour transparency film, using a wide angle lens set at F/4. Immediately over the right hand railing on the dome are trails of the stars of the Southern Cross laid on its side. The red-orange trail of the star Acrux was almost touching the railing when the exposure was started. The wavy lines at eye level are astronomer's flashlights as they walk across the scene to the dome. A much longer exposure of the same scene without moonlight is seen here.

Other star-trail images
AAT 1.   The 3.9m Anglo-Australian Telescope (AAT)
AAT 2.   An observer adjusts the UK Schmidt Telescope
AAT 3.   The telescope control console of the AAT
MISC 1. The AAT dome (forground) and the UK Schmidt building
MISC 2. The UK Schmidt buildings (foreground) and the AAT at Siding Spring
MISC 6. Moonset into cloud over the Warrumbungle Range
MISC 22. The scene as above, but without moonlight
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Updated by David Malin, 2012, March 17