Elusive polar mesospheric clouds captured by ISS astronauts
Wednesday, September 17, 2014, 11:33 AM - The view of our planet from space is amazing, but from time to time, the astronauts on board the International Space Station are able to spot an elusive treat - wispy, shining 'polar mesospheric clouds' hanging far above the planet's surface, like these ones spotted above the Ukraine on August 1, 2014.
Polar mesospheric clouds are pretty much what they sound like. They're clouds that happen over the planet's north and south poles, at mesospheric heights, or about 80 to 100 kilometres above the ground. The thin, wispy layer of ice crystals that they're composed of is virtually invisible during the day, when the sunlight is shining down through it. However, as the Sun is setting, and the rays of light from it strike this layer of ice crystals edge-on, the effect is quite spectacular.
Viewed from the ground, the 'ragged edges' of this cloud layer are known as noctilucent clouds - which means 'night shining' clouds - and these have been seen near polar regions going back to the late 1800s. It's not known if they were seen before that, as there are no records prior to 1885, so it may be a recent phenomenon, and it's still being studied to fully understand them. Studies have shown that these clouds could have an 'extraterrestrial' origin, as dust from meteors streaking through the upper atmosphere may be acting as cloud condensation nuclei. Also, considering that they've been spreading in recent years, and thus are visible much further away from the poles than usual, NASA notes that some researchers have been investigating whether climate change is responsible, as methane being released into the atmosphere spreads higher and is broken apart to form water vapour.
When spotted from space, they go by their more scientific name. In the image above, they are visible as an extremely thin layer, far above the troposphere (where all of our weather happens). However, closer up, the astronauts caught a much better view of them, showing off the subtle details.
According to NASA, astronauts who count themselves lucky enough to have spotted these clouds have referred to them as "one of the most beautiful things you can see from orbit."
(Images courtesy: NASA Earth Observatory)