How to... Catch noctilucent clouds
During long summer nights the sky can be too bright to observe some of the fainter deep-sky targets, so why not see if you can spot this stunning ghostly phenomena?
The best ways to observe and image this phenomenon
During the summer months the night sky doesn’t get dark enough to see faint stars and deep-sky objects, so many stargazers go into hibernation. Others find alternative celestial attractions to observe such as noctilucent clouds (NLC), which are clouds of ice crystals and dust that form in the upper atmosphere.
Being so high means NLCs are illuminated by the Sun’s rays at night, long after sunset. NLCs can be distinguished from other clouds because they shine behind them, silhouetting them like ink blotches.
You don’t need fancy equipment to see NLCs; they’re visible to the naked eye. However, a pair of binoculars is great because NLCs often have very fine, intricate structures – wisps, curls, streamers and billows – that can’t be seen well. NLC are very photogenic too, but you really need a digital SLR to take good images.
NLCs are only visible for northern hemisphere observers between the end of May and the end of July.
After 11:30pm on any clear night during this NLC season you should check the northern sky for signs of NLCs – typically faint wisps of blue, like silvery vapour trails. They might either fade away or develop into something more impressive – there’s no way of telling in advance what they will do.
Most NLC displays are modest affairs, restricted to a few bands or patches of glowing cloud hovering almost reluctantly above the northern horizon. But if you’re lucky enough to catch a major display of NLCs you will be blown away; there is nothing else like it in astronomy.
During a major display NLCs can form beautiful shapes – ghostly streamers, curls and tendrils of silvery-blue light. Many NLCs show a distinctive cross-hatch pattern, and binoculars will show you the insides and edges of the clouds changing shape almost by the second, sculpted by the silent winds blowing high above the Earth.
Watching NLCs requires a lot of patience. If a major display occurs you can easily be out from midnight through until dawn, so dress warmly and take snacks and a hot drink.
You’ll need to look for them from somewhere with a low, flat northern horizon without any trees, buildings or hills to block your view. If you can see the star Capella, your observing site should be fine.