Noc­tilu­cent CLOUDS

WHEN: All month, times as spec­i­fied

Sky at Night Magazine - - THE SKY GUIDE -

Noc­tilu­cent cloud (NLC) sea­son typ­i­cally runs from late May through to early Au­gust, with June and July be­ing the months most likely to de­liver a dis­play. Noc­tilu­cent or ‘night­shin­ing’ clouds are the high­est clouds on the planet, formed in the meso­sphere, in a nar­row layer 76-85km up. One of the prime seed­ing agents for their for­ma­tion is the fine dust left be­hind af­ter a me­teor va­por­ises in the at­mos­phere.

Their ap­pear­ance is not guar­an­teed and spot­ting them can be tricky at UK lat­i­tudes. There’s no guar­an­tee that they will be present on any given date and even if they are, you’ll need good clear skies, a low hori­zon and to be look­ing at the right time. They ap­pear to shine at night be­cause even when the Sun is be­low the hori­zon from the ground, from their alti­tude they can still ‘see’ it above the hori­zon. Sun­light re­flects off them and they ap­pear bright against the deep twi­light sum­mer night sky.

Look for them low down in a north­west di­rec­tion 90-120 min­utes af­ter sun­set, or a sim­i­lar time low down in the north­east be­fore sun­rise. The rea­son they ap­pear in these di­rec­tions at these times is be­cause the bright­est re­flec­tions oc­cur di­rectly above the Sun’s po­si­tion be­low the hori­zon. If a re­ally ex­ten­sive dis­play oc­curs, it’s pos­si­ble to watch it spread from the north­west, through north and through to the north­east as it tracks the Sun’s po­si­tion.

A few years ago, NLC dis­plays were widely re­ported from the UK and it be­came some­thing of a reg­u­lar ac­tiv­ity to re­port and pho­to­graph them. Over re­cent years the dis­plays have been less com­mon, but it’s al­ways worth keep­ing an eye out. If they are there, they typ­i­cally ap­pear with an elec­tric blue colour, of­ten dis­play­ing a fine net­work of rip­pling pat­terns.

Di­rec­tion and tim­ing are crit­i­cal to see­ing NLCs; a flat hori­zon is also highly rec­om­mended

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