Noctilucent Clouds: The Tallest, Driest, Coldest and Rarest Clouds on Earth

SPACE — Look north for an hour or two after sunset and before sunrise for the next few months. You’ll likely see subtle streaks of blue, silver, or gold across the skies of the Northern Hemisphere.

Called noctilucent clouds, or NLC, these odd-looking patterns in the sky are the tallest, driest, coldest, and rarest clouds on Earth. At least, that is the conclusion of a study on the 2018 phenomenon.

These glistening, shining clouds at night appear in the mesosphere, the layer of Earth’s atmosphere above the stratosphere and below the thermosphere. The place is about 76 to 85 kilometers above the Earth’s surface. Sometimes called space clouds, NLC form just below the invisible boundary where Earth’s atmosphere ends and outer space begins, approximately 62 100 km above the planet’s surface.

Scroll to read

Scroll to read

According to NASA, NLC occurs when water vapor freezes into ice crystals that stick to dust and particles left by meteors that fall in the atmosphere. It then reflects sunlight.

The peak season for observing the NLC from the Northern Hemisphere is around the summer solstice in late June through late July. At this time of year, they are most visible from about 50 to 70 degrees north latitude. However, according Spaceweather.comsome NLCs have been seen earlier this month in colder northern regions such as Denmark.

According to the Washington Post, NLC sightings were at their highest level in 15 years last summer. Sightings have become more frequent in recent years and at lower latitudes. “This is likely because climate change is producing more water vapor in the atmosphere due to increased methane in the atmosphere,” said the National Oceanic and Atmospheric Administration (NOAA).

For the best chance of seeing some NLC at night, you need a good view of the northern horizon as the stars begin to shine in the late twilight. “Views in the lower 20 to 25 degrees of the northern sky are commonplace,” wrote Sky & Telescope.

Looking at the sky with the naked eye is the best way to spot noctilucent clouds. However, using binoculars will lead you to this incredible close-up structure of one of the summer sky views. The impressive NLC, however, is still the most elusive. Source: LiveScience