Noctilucent clouds in england
© Mark Humpage/'Noctilucent' or 'night-shining' clouds form at the outer limits of the upper atmosphere and reflect the sun's light long after it has gone down over the horizon.
With the sun dappled across these white clouds and a deep blue sky, it appears dawn is about to break.

But this remarkable photograph of an English rural landscape near was taken at midnight and shows the rare phenomenon of 'night shining.'

The shimmering clouds form at an altitude of around 55 miles above sea level and are made up of tiny ice droplets. Because they are so high up in the atmosphere the sun is able to illuminate the clouds from below the horizon.

Called 'noctilucent' clouds, which literally means 'night-shining' in Latin, they are normally spotted in polar regions during the summer months.

But stunned residents spotted a rare glimpse of the clouds lighting up Leicester's skyline shortly after midnight on Thursday morning.

Noctilucent cloud formations are the highest on Earth where temperatures can plunge below -130C (-200F) and winds peak at 300mph.

They appear in the mesosphere, which is between 30 miles and 50 miles above the Earth's surface.

Clouds are made up of ice crystals and scientists are baffled as to how these form in a arid layer that is several million times drier than the Sahara Desert. But their prevalence in the summer months might be one clue.

'Upwelling winds in the summertime carry water vapor from the moist lower atmosphere toward the mesosphere,' Gary Thomas from the University of Colorado said.

The water droplets also need dust particles to stick to to create the ice crystals. This could explain why the phenomenon was first recorded in 1885, two years after the Krakatoa eruption, when several tonnes of carbon dioxide, ash and dust were emitted into the atmosphere.

However scientists do not know why the clouds have become more common since then rather than fading away. They have speculated that debris from space may be the answer.

Professor Nick Mitchell, director at the Centre for Space, Atmospheric and Oceanic Science at the University of Bath, said: 'These are beautiful and extremely special cloud formations that are a wonderful sight in our skyline.

Noctilucent explanation
© unknownThe startling illumination is caused by the sun's light reflecting back down on the Earth
'They are only visible on very clear nights during the summer months. Even after the sun has set it can still shine on the cloud formations because they are so high up.

'If people look to the north on clear summer nights after 11 pm they can often catch a glimpse of these amazing clouds. Noctilucent clouds certainly seem to be spotted with more frequency today and they are appearing brighter than ever.'

Nasa launched the AIM satellite in 2007 (Aeronomy of Ice in the Mesosphere) to try and discover why the clouds are forming and why they are changing.

It orbits 373 miles above Earth and has three instruments on board to chart the life-cycle of the clouds.

One takes pictures of the clouds, another measures the temperature of the mesosphere and how much water vapor and other gasses are present and the third sees how much dust from meteors enters Earth's atmosphere.

Despite the beauty of the clouds, scientists fear the clouds could be a sign of changes in the upper atmosphere because of global warming.

'The clouds are becoming brighter, occurring more frequently with time and they are being observed at lower latitudes than ever before,' an AIM mission expert said.

'One plausible explanation is that temperatures where the clouds form (in the higher atmosphere) have become colder with time due to the build up in the lower atmosphere of greenhouse gases from human activities.'