Halley Comete - Halley's Comet on December 9, 1985 - Halley Comete December 9, 1985

Halley Comete - Halley's Comet on December 9, 1985 - Halley Comete December 9, 1985. Photo obtained by Siding Spring's 3.9m telescope. Almost all the colour pictures from the AAT are made by combining three black and white photographs taken in red, blue and green light. Most of the objects are very distant and plates taken years apart show little change; however Halley's Comet moved rapidly through the solar system towards the sun and as the telescope followed its motion the background stars were recorded as coloured streaks, their length corresponding to the exposure times, (15, 15 and 20 minutes). The diffuse coma is tinged blue by the action of sunlight on gases evaporated from the icy nucleus, leaving behind tiny dust grains as a faint yellow tail shining by reflected sunlight