Noctilucent clouds forecast to form every 5 days from July 19 between latitudes 50° and 60° N

Unlocking secrets of 'eerie' clouds

BBC, July 19, 2010

An amateur scientist has compiled a forecast to enable observers to view a mysterious type of cloud.

The project is part of a series for BBC Radio inviting members of the public to submit their ideas for a scientific research project.

The eerie, "noctilucent clouds" clouds form at the edge of space, far higher in the atmosphere than more familiar clouds.

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 http://www.bbc.co.uk/news/science-environment-10666764