Science

Noctilucent Clouds: Everything You Need to Know About Rare ‘Night-Glowing’ Clouds

Noctilucent clouds are rare high-altitude clouds that can only be seen under certain conditions. They appear in the summer months, after sunset, as thin bluish-silvery stripes “dancing” across the sky.

According to Merriam Webster, the name silver comes from the Latin words “nocto” and “lucent”, which translates to “night” and “radiance”, respectively. (will open in a new tab).

According to NASA, they are sometimes referred to as polar mesospheric clouds. (will open in a new tab), and these special clouds that shine at night delight skywatchers during the summer months. Here we explore what they are, how they form, and how you can see them with your own eyes.

Subject: Astrophotography for beginners. How to shoot the night sky

Noctilucent Cloud Training and Location

Most of our planet’s clouds form in the closest layer of the Earth’s atmosphere to the Earth – the troposphere – at an altitude of 1.2 miles (1.9 km) to 11.4 miles (18 km). But noctilucent clouds take things to a whole new level (literally). Noctilucent clouds are located in the third layer of the Earth’s atmosphere – the mesosphere – where they form 47 to 53 miles (76 to 85 km) above the surface, making them Earth’s highest clouds.

According to the UK Met Office, noctilucent clouds require water vapor, dust and very low temperatures (like many clouds) to form. (will open in a new tab).

Noctilucent clouds are visible during the summer months, when the mesosphere is coldest at the poles, according to Earth Sky. (will open in a new tab). When the temperature is low enough, the water vapor freezes on the dust particles, forming ice crystals. When the sun shines on them from below, these ice crystals reflect the sunlight and appear in the night sky as electric blue wisps reaching towards the edge of space.

But where does all this dust come from in the mesosphere? According to the Met Office, mesospheric dust can originate from space in the form of tiny meteors or come from Earth as a result of volcanic eruptions or emissions of pollutants. According to the ESA, these strange clouds were first mentioned in 1885, two years after the Krakatoa volcano eruption. (will open in a new tab).

How to see noctilucent clouds

Noctilucent clouds form at high altitudes and are visible during astronomical twilight. In this image, noctilucent clouds and Comet NEOWISE are visible over Wroclaw, Poland. (Image credit: Piotr Mitelsky via Getty Images) (will open in a new tab)

According to the Met Office, not everyone is lucky enough to see these glowing clouds at night, as they are only visible at latitudes between 45 and 80 degrees north and south latitude.

There is a relatively small observation window for noctilucent clouds, as they are only visible after sunset during astronomical twilight during the summer months.

To increase your chances of seeing these spectacular glowing clouds at night, look for a clear patch of sky after sunset. Some helpful tips and recommended camera settings can be found on the Meandering Wild travel photography website. (will open in a new tab) there is a useful article to help photographers of noctilucent clouds. To capture the dynamic beauty of these clouds, you can also set up a low light-capable camcorder to capture time-lapse footage.

Noctilucent clouds are not only a marvel that those of us who live on Earth face, they also put on a show for orbiting astronauts on the International Space Station. In 2016, ESA astronaut Tim Peak took a picture of noctilucent clouds shimmering high above the Earth’s surface from an orbiting laboratory.

Noctilucent clouds photographed from the International Space Station by ESA astronaut Tim Peak on May 29, 2016. (Image credit: ESA/NASA) (will open in a new tab)

Are noctilucent clouds appearing more often?

Scientists have found that the frequency of noctilucent clouds fluctuates each year due to changes in the atmosphere and the solar cycle, but overall clouds are becoming more common.

A study published in July 2018 in the scientific journal Geophysical Research Letters. (will open in a new tab) explains that the increase in the appearance of these clouds shining at night is associated with an increase in greenhouse gas emissions, in particular methane.

According to Oxford University’s Institute for Environmental Change, methane is a powerful greenhouse gas that produces water vapor – a key component of noctilucent clouds – through chemical reactions, namely oxidation in the troposphere by the hydroxyl radical (OH). (will open in a new tab).

Throughout the study period, from 1871 to 2008, the scientist found that methane emissions more than doubled the amount of mesospheric ice present, increasing the likelihood of noctilucent clouds forming.

A giant balloon launched as part of NASA’s Polar Mesospheric Cloud (PMC) Turbo mission on July 8, 2018 observed these noctilucent clouds for five days and took millions of images. (Image credit: NASA/PMC Turbo/Joy Ng) (will open in a new tab)

“People living in mid- and high latitudes now have a good chance of seeing noctilucent clouds several times each summer,” said Franz-Josef Lübcken, an atmospheric researcher at the Institute for Atmospheric Physics, in a statement. Leibniz in Kühlungsborn, Germany. (will open in a new tab). “In the 19th century, they were probably only seen once every few decades or so.”

2022 has been a particularly good year for displaying noctilucent clouds, as NASA’s AIM (Aeronomy of Ice in the Mesosphere) spacecraft, with the primary goal of studying the formation of these clouds, detected the largest increase in the frequency of noctilucent clouds in 15 years.

So why the sudden increase? An emerging theory is that rocket launches are to blame.

When a rocket is launched, water vapor is released into the atmosphere. The water vapor then rises into the mesosphere for about ten days, according to Cora Randall, a professor at the University of Colorado at Boulder, in a statement on spaceweather.com. (will open in a new tab).

“We hypothesize that the surge could be caused by excess water vapor carried to higher latitudes by rocket launches,” Randall says. “But it will take a lot more quantitative analysis to confirm this or not.”

While this is just a guess, the timing seems to be consistent with a recent flash of noctilucent clouds about 10 days after a series of rocket launches.

In June 2022, SpaceX launched three missions in just over 36 hours, the third of which was the launch of the Globalstar satellite on June 19. About 10 days after the launch on June 30, Spaceweather.com documented an outburst of noctilucent clouds. In the days that followed, many took to Twitter to share their experience of seeing the noctilucent clouds.

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A recent study using NASA’s AIM satellite came to a similar conclusion that rocket launches and noctilucent cloud formation are linked.

The researchers went one step further to look at how rocket launch times affect the formation of noctilucent clouds at certain latitudes. They found that morning rocket launches are partly responsible for the appearance of noctilucent clouds at lower latitudes, according to a NASA statement. (will open in a new tab).

“The analysis revealed a strong correlation between the number of launches that occurred between 11 p.m. and 10 a.m. local time and the frequency of mid-latitude noctilucent clouds observed between 56 and 60 degrees north latitude.” says in the statement.

Noctilucent clouds are not the only side effect of rocket launches. Observers around the world are reporting other spectacular patterns in the sky, including a strange blue spiral in New Zealand and a “space jellyfish” off the coast of Florida.

Follow us on Twitter @Spacedotcom (will open in a new tab) and Facebook (will open in a new tab).

Additional Information

For more information on noctilucent clouds, contact the British Astronomical Association. (will open in a new tab) A beginner’s guide to clouds in the upper atmosphere. If you want more beautiful images of noctilucent clouds, check out the NASA AIM mission image gallery. (will open in a new tab). Explore noctilucent clouds on other planets with this article on Earth’s skies. (will open in a new tab) about the clouds shining at night on Mars.

Bibliography

Lübken, Franz Josef, Uwe Berger and Gerd Baumgarten. “On the anthropogenic impact on the long-term evolution of noctilucent clouds”. Geophysical Research Letters 45.13 (2018): 6681-6689.

American Geophysical Union. (2018, July 2). Climate change is making clouds shining at night more visible. Phys.org. Retrieved 25 July 2022 from www.phys.org/news/2018-07-climate-night-shining-clouds-visible.html.

Climatology of methane. Institute for Environmental Change. Retrieved 25 July 2022 from www.eci.ox.ac.uk/research/energy/downloads/methaneuk/chapter02.pdf.

How to find and photograph noctilucent clouds. Winding wild nature. Retrieved 25 July 2022 from www.meanderingwild.com/photographing-noctilucent-clouds/.

Loff, S. (ed.). (2017, August 7). View of noctilucent clouds from the space station. NASA. Retrieved July 25, 2022, from www.nasa.gov/image-feature/space-station-view-of-noctilucent-clouds.

Merriam Webster. Silver cloud Definition and meaning. Merriam Webster. Retrieved 25 July 2022 from www.merriam-webster.com/dictionary/noctilucent%20cloud.

Silver clouds. Met Office. Retrieved 25 July 2022 from www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/clouds/other-clouds/noctilucent.

Noctilucent clouds: the most in 15 years! EarthSky. (July 3, 2022). Retrieved 25 July 2022 from www.earthsky.org/earth/night-shining-clouds-noctilucent-clouds-how-they-form-how-to-see-them.

Silver overlays. ESA. Retrieved 25 July 2022 from www.esa.int/ESA_Multimedia/Images/2020/07/Silver_linings.

Sudden increase in noctilucent clouds. Spaceweather.com Time machine. Retrieved July 25, 2022 from www.spaceweather.com/archive.php?view=1&day=03&month=07&year=2022.

Thomas, W. (July 22, 2022). Rocket launches can create glowing clouds at night away from the poles. NASA. Retrieved July 25, 2022 from www.nasa.gov/feature/goddard/2022/sun/rocket-launches-can-create-night-shining-clouds-away-from-poles-nasa-aim-mission.

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