Comete of Halley - Halley's comet - View on April 10, 1986

Comete of Halley - Halley's comet - View April 10, 1986. Photo obtained by the 1.2m Schmidt UK Telescope from Siding Spring. 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. The comet's tails also point away from the sun, no matter what the direction of the comet. The multicoloured 'rain' is 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