NOCTILUCENT CLOUDS

 The northern season for noctilucent clouds (NLCs) is underway. Since the middle of May, NASA's AIM spacecraft has been seeing banks of electric-blue NLCs circling Earth's north pole on a regular basis. Now, observers report that the clouds are spreading south. Pete Lawrence of Selsey UK photographed this apparition on June 3th

 

"I witnessed this fine NLC display on the morning of June 3rd," says Lawrence. "My location is 50.75N so it was amazing to see the clouds so far from the poles. As dawn approached, fingers of NLC spread until they were virtually overhead!"

Noctilucent clouds (NLCs) form near the top of Earth's polar atmosphere when water vapor from the planet below mixes with meteor debris from space. They appear during summer because that is when the mesosphere is coldest and most humid. This year, NLCs appeared early, more than a full month before the solstice, setting the stage for an unusually good NLC-watching season.

High latitude sky watchers should be alert for NLCs in the evenings ahead. In recent years they have been sighted as far south as Utah, Colorado, and Nebraska. Observing tips: Look west 30 to 60 minutes after sunset when the sun has dipped 6^o to 16^o below the horizon. If you see luminous blue-white tendrils spreading across the sky, you've probably spotted a noctilucent cloud.