Look up an hour or two after sunset and before sunrise for the next few months and you may see ethereal blue, silver, or gold streaks across the northern skies of the Northern Hemisphere.
Called noctilucent clouds (meaning “night-glowing” clouds in Latin) or NLC, these strange patterns in the sky are the tallest, driest, coldest and rarest clouds on Earth, according to a study 2018 of the phenomenon.
These shimmering, glowing clouds at night appear in the mesosphere – a layer of earth’s atmosphere above the stratosphere and below the thermosphere, approximately 47 to 53 miles (76 to 85 kilometers) above the Earth’s surface. Sometimes dubbed “space clouds”, NLCs form just below the invisible boundary where Earth’s atmosphere ends and Cosmos begins, about 100 km above the surface of the planet, according to Nasa.
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NLCs occur when water vapor freezes into ice crystals that cling to dust and particles left behind by meteors falling high in the atmosphere, which reflect sunlight. According Windy. However, some NLCs have already been spotted this month in colder northern regions like Denmark, according to Spaceweather.com.
NLC sightings hit their highest level in 15 years last summer, according to the Washington Post. Sightings have become more frequent in recent years and at lower latitudes, possibly because climate change is generating more water vapor in the atmosphere due to increased atmospheric methane, according to NOAA.
To have the best chance of seeing NLCs in the evening, you’ll need a good view of the northern horizon as the stars begin to shine in late twilight. It’s typical to see displays in the lower 20 to 25 degrees of the northern sky, depending on Sky & Telescope. Naked-eye observation is the best way to find noctilucent clouds, but with a pair of best binoculars for stargazingyou’ll get a fabulous close-up of the structure of one of summer’s most elusive and awe-inspiring sky views.