AAO image reference UKS 34. « Previous || Next »
Top left is NE. Image width about 2 degrees
Image and text © 2001-2010, Australian Astronomical Observatory. Photograph from UK Schmidt plates by David Malin.
To those prepared to leave their brightly lit suburbs and seek dark skies, Comet Halley was there to be enjoyed in late 1985 and the first few months of 1986, especially in the southern hemisphere. The warming action of sunlight on the tiny nucleus of the comet evaporates volatile materials from its surface which expand rapidly in the vacuum of space, producing the large coma. Solar radiation pressure sweeps back this tenuous cloud into the typical comet shape. Emerging from the coma, two distinct tails can often be seen. The blue one is primarily due to volatile molecules such as water, carbon dioxide and carbon monoxide dissociated by ultraviolet sunlight, fluorescing in the blue colour of the cyanogen radical, while the faint yellow streak is sunlight reflected from dust particles liberated from the nucleus along with the volatile materials.
This picture was made after the comet had rounded the sun and was heading back into the cold of interstellar space. In 2023 it will be as distant as Pluto, where it will begin to fall towards the Sun, arriving in mid-2061. A comet's tail always points away from the sun, irrespective of the direction of the comet through space, and it is foreshortened in this photograph. The multicoloured 'rain' seen here are the trails of countless stars, photographed, like the comet, in red, green and blue light as the UK Schmidt Telescope followed the comet's motion in front of the Milky Way. A more detailed, shorter exposure was taken a few months earlier by Anglo-Australian Telescope.
Related images, other comets
AAT 46. Halley's Comet, December, 1985
AAT 117. Halley's Comet, April 9-10, 1986 (AAT image)
UKS 19. Halley's Comet on 12 March, 1986
UKS 19a Features in the dust tail of Comet Halley, 12 March, 1986
UKS 33. Comet Hyukatake, March, 1996
MISC 20. Comet Halley hanging in the Milky Way in 1986.
For details of object position and photographic exposure, search technical table by UKS reference number.