Noctilucent Cloud Season Begins

When noctilucent clouds (NLCs) first appeared in the 19th century, they were a high-latitude phenomenon. You had to travel toward the poles to see their electric-blue glow. Not anymore. Just this past weekend, these beautiful, "night-shining" clouds spilled over the Canadian border into the lower United States as far south as Denver, Colorado.

In recent years, a NASA spacecraft called AIM (Aeronomy of Ice in the Mesosphere) has spotted the clouds appearing ever lower in latitudes, but just why is not yet known. AIM studies the clouds in order to better understand our lower atmosphere and how it is connected to weather and climate.

The clouds are seasonal, appearing most often in late spring and summer. In the northern hemisphere, the best time to search for these beauties would be between mid-May and the end of August.