Stratospheric Sunsets

Polar stratospheric clouds can give some unusual sunsets because of their high altitude of around 20 km, the sunset display on 18th February 2008 was widely observed. The top two images were taken on the evening of 17th February while the lower images are from the more impressive sunset of 18th February.

There seemed to be something subtly different about this sunset on the 17th. Here the sun was 4 degrees below the horizon and seemed to be lighting up higher cloud than normal.	By the time the sun was 5.4 degrees below the horizon there was a faint purple glow at the top of the sunset colours, however this soon faded.

Sunset on February 18th with the sun 5.5 degrees below the horizon. The same altitude and exposure as the previous night shows the purple glow is much brighter and more extensive.	Seven minutes later the sun had dropped to 6.7 degrees below the horizon and the purple light had faded, leaving this deep red glow.
	This shadow ray on the left edge of the display persisted for nearly ten minutes.

Canon EOS 20D 17th and 18th February 2008
Wiltshire, England