Pinatubo dust colours the twilight
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Image and text © 1985-2002, Australian Astronomical Observatory, Photograph by David Malin.

On June 15, 1991, after weeks of rumbling and venting steam and poisonous gas, Mt Pinatubo exploded on the island of Luzon, in the Phillipines. This was the largest volcanic eruption for nearly a century. The eruption killed over 700 people and ejected several cubic kilometers of dust and gas over 35km high into the stratosphere.

The effects were felt around the world and included a temporary global cooling and a thinning of the ozone layer as well as other changes in the global weather pattern. However, the most obvious effect for many people was a milkiness in the daytime sky due to scattering by high altitude aerosols, and corresponding anomalous sunsets and twilights that were noticable for years.

This picture was made in early 1992, a little after sunset from alongside the AAT dome at Siding Spring, looking west. Not only was the colour of the sky unusual, but the yellow-orange glow extended all the way to the zenith (immediately overhead). At this time the stratospheric dust was still in sunlight and it reflected the colours of the setting sun widely across the sky. For at least two years the twilights were longer than usual and extended and a red horizon glow remained for visible several hours after sunset. Its reflection in the AAT dome several hours later is seen here.

Related image
MISC 7.   Star trails around the AAT dome, after Pinatubo sunset.

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Updated by David Malin, 2012, March 17