The Season of Noctilucent Clouds Arrives; the Only Ones that Glow at Dusk

The cottony agglomerations that flood the sky do not always have the same constitution; there are those of different colors, altitudes, and weights. You might be surprised to discover that some clouds weigh thousands of tons. But in addition to their classification by morphology, there are also seasonal ones, such as the ethereal noctilucent clouds that appear during the summer. The time is approaching when they can be seen more in the celestial dome, although some have already begun to observe them on the horizon.

What Are Noctilucent Clouds?

We are used to looking for clouds at the time when there is the most sunlight because, normally, the sun’s rays pass through them like needles and illuminate them in a way that contrasts with the blue sky of the atmosphere. Another time to hunt for clouds is during thunderstorms when the untamed cumulonimbus rises to warn us that they will drain a large amount of water over our heads.

Rarely do we have the opportunity to observe cloud agglomerations during twilight and that is why noctilucent clouds are special. Their name says it all, translated from Latin, noctilucent means ‘clouds that glow at night,’ and the best time to see them rise far above the average height of a conventional cloud.

Noctilucent clouds (NLC) are the highest, driest, coldest, and rarest clouds on the planet. These bright formations that rise beyond twilight appear in the mesosphere, which is the layer of the Earth’s atmosphere that rises above the stratosphere and below the thermosphere. This makes them the highest altitude clouds, forming where the invisible boundary between the atmosphere and outer space known as the Kármán Line is drawn, approximately 100 kilometers above the surface of the planet, according to NASA.

Unlike other clouds, noctilucent clouds, or space clouds, do not appear as an agglomeration of absorbent cotton, but as a set of ethereal lines extending towards the horizon, which is due to how they are constructed. NLCs occur when water vapor freezes into ice crystals that then adhere to dust and particles left in their wake by meteorites that incidentally fall into the atmosphere. Optics works its magic and causes the crystals to break up the light that still manages to reach them so that from our perspective they shine like nocturnal rainbows.

When Is the Noctilucent Cloud Season?

From the northern hemisphere, the best season to see noctilucent clouds is during the summer, on days close to the solstice. From late June through late July, ideal conditions exist for the rarest and highest clouds to appear in the atmosphere.

Look for them a few hours after sunset and before sunrise at approximately 50 to 70 degrees north latitude. You will need a clear view to the north, as they usually appear not at the zenith, but on the horizon. They are beautiful to the naked eye, and in fact, this is the best way to delight in noctilucent clouds, but if you have a pair of powerful binoculars, you can get a close-up view of the structure of one of the most elusive and impressive sky views.

Story written in Spanish by Alejandra Martínez in Ecoosfera

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