The summer solstice, which takes place at 5:13 a.m. EDT on June 21, ushers in the year’s longest season, a shade over 93 days, according to timeanddate.com. The summer season also creates a unique phenomenon in the sky, known as noctilucent clouds. The clouds, also called “electric blue clouds,” are formed approximately 50 miles above the Earth’s surface, nearly touching the edge of space. Comparatively, most clouds form in the lowest 10 miles of the atmosphere.
In the beginning stages of summer, the high-altitude clouds are able to be viewed in the Northern Hemisphere, whereas viewers in the Southern Hemisphere are able to spot the noctilucent clouds in December and January. Typically, the clouds are most visible in areas between 45 and 60 degrees latitude, according to EarthSky.
North American cities in that range include Seattle, Minneapolis, Montreal and Calgary. However, recent years have set records for lower latitude sightings, with observations recorded in Las Vegas (36 degrees) and Los Angeles (34 degrees).
Timing is also important to catch the wondrous clouds in action, as they can only be typically viewed during a two-hour period after sunset in the western sky, or the two-hour period before sunrise in the eastern sky. During these times, the sun is below the horizon from the perspective of the ground, but its light is still able to reach the high altitude where noctilucent clouds form. Therefore, the sunlight illuminates the clouds, allowing them to glow in the night sky. One telltale sign of the clouds can be seen about 30 minutes after sunset. When bright blue and white-colored tendrils spread across the sky, that’s a prime indicator of a noctilucent cloud.
The noctilucent cloud is said to be made up of ice crystals that form on dust particles left behind by meteors. Their formation occurs when water is around to form the ice crystals, and when temperatures are very low. Despite summer being warmer on the ground, the coldest conditions of the year in the cloud’s high altitudes take place during the season, an impetus for cloud formation. Temperatures in the high atmosphere, also known as the mesosphere, can drop to below 200 degrees F below zero, usually reaching the frigid conditions by the middle of May.
Noctilucent clouds also have the potential to be a human-made event, specifically as the result of rocket launches into space. In early May, a launch from SpaceX’s Falcon 9 rocket left behind a stunning cloud referred to as a “space jellyfish,” sharing many characteristics with noctilucent clouds, including the blue and white glow.
Scientists have been observing noctilucent clouds for years using the NASA Aeronomy of Ice in the Mesosphere satellite, collecting data about temperatures, atmospheric gases, ice crystal sizes and changes to the clouds. For citizens looking to view the phenomenon, luckily, they do not need a NASA connection, just a trained eye ready to view the blue and white wonder.
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