Astronauts aboard the International Space Station (ISS) sometimes see what are called polar mesospheric clouds by scientists – noctilucent or night-shining clouds by the rest of us. As seen from Earth’s surface, these clouds have a short season when they are most often seen: that is, late spring to early summer. They shine at full intensity over a period of no more than five to 10 days. From Earth’s surface, they are only seen at high latitudes, in the Arctic or Antarctic. And they are most often seen either before sunrise or after sunset. The images below, however, are taken from space and know no such limitations. Astronauts aboard ISS see these clouds at all times of year, and sometimes far into the night. The first image is very recent, taken on January 5, 2013.
Most of the time, when astronauts aboard ISS acquire images of night-shining clouds, they use a relatively short focal length lens to maximize the field of view. The image above, however, was taken with a long lens (400 mm), which provides some additional detail of the cloud forms, NASA says. Below the brightly-lit noctilucent clouds, across the center of the image, the pale orange band is Earth’s stratosphere.
Night-shining form high above Earth, in a region of the atmosphere called the mesosphere. They typically form between 76 to 85 kilometers (47 to 53 miles) above Earth’s surface. After sunset or before sunrise, when the sun is below the horizon seen from the ground – but visible from the high altitude of noctilucent clouds – sunlight illuminates these clouds. In much the same way, you might sometimes see a high-flying aircraft illuminated by sunlight after the sun has set for you on the ground.
No one knows exactly what causes these clouds. Some say meteors, or rocket exhaust. Others say there is a climate connection and that changes in atmospheric gas composition or temperature has caused the clouds to become brighter over time. It is known that night-shining clouds can only form when temperatures are very low and when there’s water available to form ice crystals.
In the image above – taken on June 13, 2012 – the night-shining clouds are trending across the center of the image. Plus you can see that lower layers of the atmosphere are also illuminated. The lowest layer of the atmosphere visible in this image — the stratosphere — is indicated by dim orange and red tones near the horizon. Read more about this image here. On the same date this image was taken from space, night-shining clouds were also visible to aircraft flying over Canada.
The unusual photo above shows night-shining clouds illuminated by the rising, rather than setting sun. Low clouds on the horizon appear yellow and orange, while higher clouds and aerosols (particles like dust and pollution) are illuminated a brilliant white. The night-shining clouds appear as light blue ribbons extending across the top of the image. The International Space Station was over the Greek island of Kos in the Aegean Sea (near the southwestern coastline of Turkey) when astronauts on board acquired this image at approximately midnight local time on June 16, 2010. Read more about this image here.
ISS captured the image above at approximately 38 minutes after midnight Greenwich Mean Time (GMT) on January 30, 2010, as the space station passed over the southern Atlantic Ocean. January in Antarctica is summertime, and the sun never sets, but rather traces an arc across the local horizon. That’s why night-shining clouds – which are typically seen close to the time of sunset or sunrise – can be observed near local midnight at that location, at that time of year. In this image, the clouds appear as thin, wispy light blue forms that contrast with the darkness of space (image upper right). Lower levels of the clouds are more strongly illuminated by the sun and appear light orange to white. Clouds closest to the Earth’s surface are reddish-orange (image center). Read more about this image here.
An astronaut aboard ISS acquired the photo above – showing night-shining clouds before dawn on July 22, 2008 – as the space station passed over western Mongolia in central Asia. ISS was flying at an altitude of just over 200 miles (about 321 kilometers). The dark horizon of the Earth appears at the bottom of the image, with some layers of the lower atmosphere already illuminated by the rising sun. The higher, bluish-colored clouds look much like wispy cirrus clouds, which can be found as high as 60,000 feet (18 kilometers) in the atmosphere. However noctilucent clouds, as seen here, are observed in the mesosphere at altitudes of 250,000 to 280,000 feet (about 76 to 85 kilometers). NASA says that observations of night-shining clouds over northern Asia in June and July aren’t uncommon. Read more about this image here.
Bottom line: A gallery of images, taken by astronauts aboard the International Space Station (ISS), showing what are called polar mesospheric clouds, or, more commonly, noctilucent or night-shining clouds.