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Fly the Cloudy Skies

I haven’t posted anything in the last couple of weeks due to my being “stranded” in the delightful island of Sark by the Eyjafjallajökul volcano eruption in Iceland which grounded most flights into and out of the UK for a week.

The view of the Icelandic Volcano from our cottage in Sark

There was no real hardship being on Sark for an extra week, especially given that every single night we were there it was clear (and dark). Indeed it seemed clearer on the nights during the air flight ban, and the daytime skies certainly contained fewer, if any, clouds. And no contrails.

Contrails over Europe

These facts are related, as contrails from planes quickly disipate in the atmosphere, spreading out to become indistinguishable from thin cirrus or cirrostratus clouds.

Contrails, short for “condensation trails”, are the visible trails of condensed water vapour in the sky left behind by exhausts of aircraft. They are, essentially, man-made clouds.

This got me thinking; just how much of the “cloud cover” that affects astronomers so badly is down to contrails?

It turns out I’m not the only one worrying about this. In fact it’s been thought a problem for quite some time.

Gerry Gilmore, of Cambridge University (and of Max Alexander‘s excellent Explorers of the Universe portrait exhibition) was saying back in 2006 that the problem of contrails might make ground based telescopes worthless by the year 2050. One small reason, amongst many, to limit our use of planes.

The last time there was such a significant drop in the number of planes in the sky was after the terrorist attacks of 11 September 2001, and back then astronauts on board the International Space Station noticed a decrease in the number of contrails over the US.

The same was true between 16 and 22 April 2010 when, for a few days, flights over Europe stopped, stranding thousands overseas, but giving a brief and welcome respite to astronomers who were able, for once, to enjoy truly clear skies.

For more info than you could ever want on contrails and their impact on ground-based astronomy, see Holger Pederson’s website with links to many articles and reports.

Also worth a look is the apparently now-defunct National Contrail Network, which formed a part of a masters research project at the University of Lancashire. The official homepage link doesn’t work, but there’s plenty of data and info that is accessible.

National Contrail Network

Finally, have a look at the Cloud Appreciation Society‘s gallery of contrail images:  they’re actually rather beautiful.

Trails and Halo, Denmark © Jesper Grønne.

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