Earth’s Highest Clouds Shine at the “Top of the Orbit”

Looking for a new desktop background? This might do nicely: a photo of noctilucent “night-shining” clouds seen above a midnight Sun over Alaska, taken from the ISS as it passed over the Aleutian Islands just after midnight local time on Sunday, August 4.

When this photo was taken Space Station was at the “top of the orbit” — 51.6 ºN, the northernmost latitude that it reaches during its travels around the planet.

According to the NASA Earth Observatory site, “some astronauts say these wispy, iridescent clouds are the most beautiful phenomena they see from orbit.” So just what are they? Read on…

Found about 83 km (51 miles) up, noctilucent clouds (also called polar mesospheric clouds, or PMCs) are the highest cloud formations in Earth’s atmosphere. They form when there is just enough water vapor present to freeze into ice crystals. The icy clouds are illuminated by the Sun when it’s just below the horizon, after darkness has fallen or just before sunrise, giving them their eponymous property.

NLCs seen in the southern hemisphere in Jan. 2010 (NASA)
NLCs seen in the southern hemisphere in Jan. 2010 (NASA)

Noctilucent clouds have also been associated with rocket launches, space shuttle re-entries, and meteoroids, due to the added injection of water vapor and upper-atmospheric disturbances associated with each. Also, for some reason this year the clouds appeared a week early.

Read more: Noctilucent Clouds — Electric Blue Visitors from the Twilight Zone

Some data suggest that these clouds are becoming brighter and appearing at lower latitudes, perhaps as an effect of global warming putting more greenhouse gases like methane into the atmosphere.

“When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor,” said James Russell, the principal investigator of NASA’s Aeronomy of Ice in the Mesosphere (AIM) project and a professor at Hampton University. “This extra water vapor is then available to grow ice crystals for NLCs.”

A comparison of noctilucent cloud formation from 2012 and 2013 has been compiled using data from the AIM spacecraft. You can see the sequence here.

And for an incredible motion sequence of noctilucent clouds — taken from down on the ground — check out the time-lapse video below by Maciej Winiarczyk, coincidentally made at around the same time as the ISS photo above:

(The video was featured as the Astronomy Picture of the Day (APOD) for August 19, 2013.)

Source: NASA Earth Observatory

An Early Start for Noctilucent Clouds

The season for noctilucent “night-shining” clouds is arriving in the northern hemisphere, when wispy, glowing tendrils of high-altitude ice crystals may be seen around the upper latitudes, shining long after the Sun has set. Found about 83 km (51 miles) up, noctilucent clouds (also called polar mesospheric clouds) are the highest cloud formations in the atmosphere. They’ve been associated with rocket launches and space shuttle re-entries and are now thought to also be associated with meteor activity… and for some reason, this year they showed up a week early.


Noctilucent clouds (NLCs) form between 76 to 85 kilometers (47 to 53 miles) above Earth’s surface when there is just enough water vapor to freeze into ice crystals. The icy clouds are illuminated by the Sun when it is just below the horizon, after darkness has fallen, giving them their night-shining properties. This year NASA’s AIM spacecraft, which is orbiting Earth on a mission to study high-altitude ice, started seeing noctilucent clouds on May 13th.

AIM map of noctilucent clouds over the north pole on June 8 (Credit: LASP/University of Colorado)
AIM map of noctilucent clouds over the north pole on June 8
(Credit: LASP/University of Colorado)

“The 2013 season is remarkable because it started in the northern hemisphere a week earlier than any other season that AIM has observed,” reports Cora Randall of the Laboratory for Atmospheric and Space Physics at the University of Colorado. “This is quite possibly earlier than ever before.”

The early start is extra-puzzling because of the solar cycle. Researchers have long known that NLCs tend to peak during solar minimum and bottom-out during solar maximum — a fairly strong anti-correlation. “If anything, we would have expected a later start this year because the solar cycle is near its maximum,” Randall says. “So much for expectations.”

Read more on the NASA AIM page here, and watch the [email protected] video below for the full story. (Also, check out some very nice NLC photos taken last week in the UK by Stuart Atkinson at Cumbrian Sky.)

Source: NASA

Coming Soon – Night Shining Noctilucent Clouds

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Soon you may see an eerie spectacle on clear summer nights if you are located at latitudes between 50° and 70° north and south of the equator: Noctilucent Clouds.

These ghostly apparitions are a delight to see and are quite rare. It is incredibly difficult to predict exactly when they will appear, but we do know they should begin to appear soon.

The season for Noctilucent Clouds (Noctilucent = Latin for “Night Shining”) starts early June and continues into late July. They are seen just after dusk, or before dawn and an apparition can last around an hour.

These mysterious clouds, with their bizarre tenuous wispy shapes reminiscent of ripples in sand or the changing surface of a pool of water, spread like a glowing web across the northern sky. Colours can range from brilliant whites, with tinges of blue, pink and orange.

Formed by tiny ice crystals, they are the highest clouds in the Earth’s atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometers (47 to 53 miles) almost at the edge of space.

They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon, while the lower layers of the atmosphere are in the Earth’s shadow. Noctilucent clouds are not fully understood and are a recently discovered meteorological phenomenon, only being recorded for about 120 years.

Noctilucent clouds can only form under very restrictive conditions, and their occurrence can be used as a guide to changes in the upper atmosphere. Since their relatively recent classification, the occurrence of noctilucent clouds appears to be increasing in frequency, brightness and extent.

There is evidence that the relatively recent appearance of noctilucent clouds and their gradual increase, may be linked to climate change. Another recent theory is that some of these bright displays come from particulates and water vapour in the atmosphere left over from Space Shuttle launches.

How can you see them? Over the next couple of months look north during dusk and dawn and try and spot this mysterious and elusive phenomenon. They are best seen when the sun is between 6 and 16 degrees below the horizon, and seem to occur more frequently in the Northern hemisphere than the Southern.

Good luck!

Noctilucent clouds over Blair, Nebraska, USA. Credit: Mike Hollingshead