Posted on by Jason Major

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

Polar mesospheric clouds shine over a midnight sunrise above Alaska on August 4, 2013 (NASA)

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

Posted on by Jason Major

An Early Start for Noctilucent Clouds

Noctilucent clouds photographed over Killygordon, Ireland on the morning of June 10. (© Brendan Alexander/Donegal Skies. All rights reserved.)

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