Twitter was a-buzz yesterday evening (1 Feb 2016) and this morning, as users took snaps of a very rare display of Nacreous Clouds over the UK.
These clouds, also known as Polar Stratospheric Clouds, form high up in our atmosphere (in the stratosphere) between 15 and 25 km in altitude. Normally this part of our atmosphere is very dry but in polar winter temperatures can plunge and conditions can become right for certain clouds to form.
The following pictures were just some of those re-tweeted by @Virtualastro last night; give him a follow to keep up to date.
Nacreous Clouds (named that after the word “nacre”, for mother-of-pearl, due to their iridescent colours) appear when sunlight is scattered through the cloud, and particles within the cloud then produce colours through diffraction processes, making for a beautiful display.
To see a display of Nacreous Clouds you have to head out when the Sun is below the horizon – but only just – during Civil Twilight – when the Sun is between 0 and 6° below the horizon. Look towards the direction of sunset or sunrise (depending on whether you’re out in the evening or morning), you may see these beautiful clouds for yourself.
Find out your civil twilight times at timeanddate.com. For central Scotland (where I am) the best time to see these clouds is between 0730-0810 and 1650-1730. Remember, these clouds are incredibly rare – you can go years without seeing such a display – and there’s no way to predict whether you’ll see them on any given night, but as they happened last night there’s a good chance they might happen again tonight or the following night, 2 or 3 Feb 2016. Get outside and look up!