Earth's highest, coldest, rarest clouds are back. How to see the eerie 'noctilucent clouds' this summer.

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Look North as the stars appear in June and July to have a chance of seeing rare noctilucent (or 'night-shining') clouds with the naked eye.

Wispy white noctilucent clouds swirl over an orange sunset and blue sea
Noctilucent clouds form when water vapor freezes onto dust particles left by meteoroids high in the atmosphere. (Image credit: Getty)

Look up an hour or two after sunset and before sunrise over the next few months and you may see ethereal blue, silver or golden streaks in the Northern Hemisphere's northern skies. 

Called noctilucent clouds (meaning "night-shining" clouds in Latin) or NLCs, these strange-looking patterns in the sky are the highest, driest, coldest and rarest clouds on Earth, according to a 2018 study of the phenomenon. 

NLCs occur when water vapor freezes into ice crystals that cling to dust and particles left by falling meteors high in the atmosphere, which reflect sunlight. The peak season for observing NLCs from the Northern Hemisphere is around the summer solstice in late June through the end of July, when they're most easily visible from about 50 to 70 degrees north latitude, according to Windy. However, some NLCs have already been spotted this month in colder, northern regions like Denmark, according to Spaceweather.com.

Noctilucent clouds spotted by the International Space Station as it passed over the Tibetan Plateau in June 2012. (Image credit: Image Science and Analysis Laboratory, NASA/Johnson Space Center)

NLC sightings were at a 15-year high last summer, according to the Washington Post. Sightings have become more frequent in recent years and at lower latitudes, possibly because climate change generates more water vapor in the atmosphere as a result of increased atmospheric methane, according to NOAA.

For the best chance to see some NLCs in the evening, you'll need a good view low to the northern horizon as the stars begin to shine in late twilight. It's typical to see displays in the bottom 20 to 25 degrees of the northern sky, according to Sky & Telescope. Naked eye viewing is the best way to find noctilucent clouds, but with a pair of the best binoculars for stargazing, you'll get a fabulous close-up of the structure of one of the summer's most elusive and impressive sky sights. 

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Jamie Carter
Jamie Carter
Live Science contributor

Jamie Carter is a Cardiff, U.K.-based freelance science journalist and a regular contributor to Live Science. He is the author of A Stargazing Program For Beginners and co-author of The Eclipse Effect, and leads international stargazing and eclipse-chasing tours. His work appears regularly in Space.com, Forbes, New Scientist, BBC Sky at Night, Sky & Telescope, and other major science and astronomy publications. He is also the editor of WhenIsTheNextEclipse.com.