Nacreous clouds have been lighting up the skies over northern England.
Also known as "mother of pearl" clouds, the clouds have been giving a spectacular display of colour which slowly swirled and meandered in the semi-dark sky earlier this week.
Nacreous clouds are rare clouds which are much higher than "usual" clouds, approximately 15km above the earth.
They form at temperatures of around -80C and contain supercooled water, ice crystals and nitric acid. This mixture scatters light in a way that produces the distinctive iridescent displays.
They are visible when the sun has just dipped below the horizon, or just before sunrise. At this point the landscape is in darkness, but being high up in the atmosphere, the nacreous clouds are still lit up by the sun.
The clouds are usually only seen near the polar regions, but sometimes the cold air in the upper atmosphere can drift away from the poles. When this happens the clouds can sometimes be spotted above the UK.