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?

All About Space - - Contents -

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.

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