Tue, 26 Jun 2012

Look out for shimmering night clouds

Clouds are usually the last thing that astronomers want to see when they go out to view the sky. But this is the time of year when a mysterious type of cloud at the edge of space may appear to dazzle observers.

These electric-blue wisps show up during summer months in the northern part of the sky. They are usually more common in northern latitudes, but this week a bright display was visible in the far south of the UK.

NLC photographed by SPA member Pete Lawrence from Selsey, West Sussex, on June 24/25, 2012

The phenomenon is known as noctilucent (night-shining) or mesopheric clouds. They form more than 80km up and have been seen from the International Space Station too. It is not difficult to tell the difference between noctilucent clouds (NLC) and ordinary weather clouds because the former can be seen shimmering brightly long after the Sun has set below the horizon.

Why they occur is still not fully understood, but their beauty may be due to a serious cause in the form of increased pollution or climate change. Other suggestions include meteoric dust or rocket exhaust. Latest research suggests that changes in the make-up of atmospheric gas or its temperature has caused the clouds to become brighter in recent years.

The SPA Aurora Section welcomes reports of these interesting atmospheric spectacles and have a guide on how to view them. They also make a very photogenic subject, so do try to capture them with your camera if you can keep it steady, e.g. with a tripod.

Added by: Paul Sutherland