NOC­TUR­NAL DIS­PLAY

Landscape (UK) - - Our Landscape -

Clear sum­mer nights of­fer the op­por­tu­nity to view rare noc­tilu­cent clouds. Vis­i­ble in north­ern skies from late May to Au­gust, th­ese are thin, streaky clouds with large bil­low or wave pat­terns. The high­est clouds in the at­mos­phere, they form ap­prox­i­mately 50 miles up. It is their height which al­lows them to be vis­i­ble af­ter the sun has set. Thought to be made of ice crys­tals, they are usu­ally bluish or sil­very but may also be or­ange or red­dish in colour. Noc­tilu­cent clouds can be seen from ap­prox­i­mately an hour af­ter sun­set. As a rule they move from east to west, which is the op­po­site way to typ­i­cal weather clouds. Peak bright­ness is reached quickly then fades un­til the point where the sun has passed its low­est point be­low the hori­zon. Pre-sun­rise dis­plays then brighten, and may be even more strik­ing than evening ap­pear­ances.

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