Alert! NLCs Predicted for Tonight!

For two nights in a row noctilucent clouds (NLCs) have swept across European skies. Photographs were taken as far south as France. Dr Tony Phillips, the author of Spaceweather.com, on June 16 says that the prediction is for a couple of more nights of NLC activity. Summer is NLC season! He also says that since NLCs were seen as low as France, norther American states, the ones that normally witness aurora displays, stand a good chance of seeing an NLC display!

Why Is This Interesting?
It is interesting for a few reasons. First. nobody knows what forms NLCs. That's right: They are an unsolved mystery. NLCs form in the mesosphere where there never used to be an water molecules or dust particles from which clouds form. But...now we have NLCs in the mesosphere that are formed primarily from water and dust. How these things got in the mesosphere is a mystery.

Also, the satellite AIM was launched in April to study NLCs, which when they are studied from space become Polar Mesospheric Clouds (PMCs). During its two year mission AIM will collect data that will, it is hoped, reveal the mysteries behind the source(s) and existence of NLCs, which were first sighted in 1884. The acapela singing group The Chromatics wrote and perform the AIM mission theme song about noctilucent clouds, our "ghostly shinning polar shroud" and "atmospheric mystery." Be sure to listen; lyrics are provided.

The other reason is that in terms of the history of the planet, NLCs are new. They have been observed for only a little over a century. Furthermore, they used to be confined to the most remote regions around the poles. Now they have spread and brightened. Each year they are seen at lower and lower latitudes and they are brighter (and I think more thick) than before. So seeing a display of NLCs is participating in an historic event, especially at lower latitudes.

What do NLCs look like?
NLCs look like brightly lit tendrils of shinning white or blue wisps. They look brightly lit because they are. Forming in the mesosphere at about 80 miles above Earth, they catch the rays of the setting sun. This is why they can seem to shine electric blue and appear iridescent. Spaceweather.com set up a new NLC Gallery for the 2007 NLC season. This is in addition to the previous NLC Gallery.

Regular weather clouds form in the troposphere which is much closer to Earth. The sun's rays leave the troposphere in darkness much sooner than in the higher mesosphere, which is actually the atmospheric layer at the edge of space. If you happen to see NLCs on a night when there are tropospheric clouds in the sky also, the tropospheric clouds will look a sunless, lightless dark gray below the brightly lit mesospheric clouds.

When and where should I look for them?
The prediction is that there may be another two or three nights of NLC display that may be visible from the northern U. S. To see an NLC display, between 30 and 60 minutes after sundown, go outside and look west. The sun needs to be between 6 degrees and 16 degrees below the horizon. This is because before then, the sun's rays slant into lower layers of atmosphere and after that the rays don't round the Earth's circumference.

NLCs come down from the polar region where they originate but you view them by looking west because that's where the afterglow of light illuminates the mesosphere. I have never yet witnessed an NLC display myself yet, but I have seen images of vast extents of sky covered in NLCs. So, in a vivid display, seeing only the western manifestation of it is not necessarily very restrictive.

NLC season is the summer months. There may be many displays of NLCs this summer, since the season has only just begun. The Southern hemisphere is in winter now. The southern NLC season does not coincide with the northern. I hope some of you see this article soon enough to look for NLCs on June 16, 17, and 18. Happy hunting! Oh! And remember to have camera in hand!

Dr. Tony Philips, "NLC Alert." June 16, 2007 Spaceweather.com. URL: http://www.spaceweather.com/