When To See Weird ‘Space Clouds' Glow After Sunset — And What They Are
Noctilucent clouds are reflected in a puddle in Sieversdorf, Germany, 5 July 2016. (Photo by Patrick ... More Pleul/picture alliance via Getty Images)
If you're in the northern hemisphere and it's been a clear day, look at the northeastern night sky before bed. You may see something astonishingly beautiful — noctilucent ("night shining") clouds.
These high-altitude clouds, formed in the coldest place in Earth's atmosphere at the edge of space, result from dust left by "shooting stars."
Here's everything you need to know about the beginning of the noctilucent cloud season — and when and where to see them.
Noctilucent clouds are Earth's highest clouds. They form between Earth and space, about 47–53 miles (76 to 85 kilometers) above the ground in the mesosphere.
Noctilucent clouds can only be seen at twilight, shining after sunset, but they are never guaranteed. Visible as vast, wispy electric blue structures, they glow surprisingly brightly as blueish or silvery streaks in the twilight sky. They do so because, during the observation season, the sun is never far beneath the horizon, so it can illuminate the clouds for some time after it appears to have set, as seen from the Earth's surface. You don't need any special equipment to see noctilucent clouds.
A superb and extensive 'grand display' of noctilucent clouds at dawn on July 16, 2022. (Photo by: ... More Alan Dyer/VW Pics/Universal Images Group via Getty Images)
Noctilucent clouds are only seen in very limited times of day and times of year, depending on your location. The farther from the equator you are, the more likely you are to see them. They're typically seen from late May to August in the Northern Hemisphere and from November to February in the Southern Hemisphere. The timing means they effectively replace the possibility of aurora, but are sometimes confused with them.
Noctilucent clouds form in the mesosphere, a layer of Earth's atmosphere about 22 miles (35 kilometers) thick. According to NASA, summer in the Northern and Southern Hemisphere is when the mesosphere is most humid, with water vapor rising from lower altitudes. Water vapor is one of the three essential ingredients for noctilucent clouds.
Noctilucent clouds are thin, wispy clouds hovering at the edge of space.
Noctilucent clouds are seeded by microscopic debris from disintegrating meteors and micro-meteors — "shooting stars!" When you see a shooting star streak across the sky, it's doing so in the mesosphere, where the friction of it hitting gases causes energy to be released as photons. As it disintegrates, it leaves a dust of sodium and iron atoms that settle upon tiny ice crystals that form in the -120°C (-184°F) temperatures. That also makes noctilucent clouds Earth's coldest clouds. Mix water vapor with meteoric dust and very cold temperatures, and the result can be noctilucent clouds.
The sodium and iron atoms in the mesosphere are highly reflective. Enormous telescopes fire lasers at this part of the Earth's atmosphere to align their optics and correct for any turbulence. It also means that the metal-coated ice grains in noctilucent clouds reflect radar and, in theory, a lot of light. However, what you see when you look at noctilucent clouds is not the collective brightness of all the metal-coated ice grains but ripples within them reflecting as one, according to researchers at Caltech.
An 1886 sketch by William Ascroft, documenting the meteorological effects of the eruption of ... More Krakatoa. (Photo)
Noctilucent clouds are not an ancient sky sight. They were first observed in 1885, across the world, in the wake of the eruption of Krakatoa in Indonesia in 1883 — one of the most significant volcanic events ever recorded — which sent up a massive plume of ash into Earth's atmosphere. During the 20th century, they were seen more regularly between 40 and 50 degrees north latitude. NASA's Aeronomy of Ice in the Mesosphere (AIM) mission has been studying them since 2007 to determine if the mesosphere is changing and how that's linked to Earth's climate and/or the solar cycle.
Wishing you clear skies and wide eyes.
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