Unlike ordinary clouds, NLCs are located extremely high, approximately 85 km above the Earth's surface, and are not visible during the day. They only become visible at dusk or dawn thanks to their illumination by the Sun, which is deep below the horizon at that time, making the clouds stand out as whitish, silvery, or electric blue veils low above the northern horizon against the dark sky. They occur most frequently in the weeks around the summer solstice, which this year falls on June 21st. If they are prominent, they can even be captured on smartphone cameras.

In the weeks around the summer solstice

Unlike normal clouds, which are found at a maximum altitude of 15 kilometers (and in rare cases up to 20 kilometers in the case of storm clouds), noctilucent clouds are found significantly higher – in the mesosphere, approximately 85 kilometers above the Earth's surface. These rare clouds only form when the temperature in the mesosphere is stable at around -130°, which occurs during the summer solstice (in the northern hemisphere, this is around June 21st). The first observations of these clouds date back to the late 19th century, but the development of digital photography, especially in recent years, has made it possible to record them easily and frequently around the world. Due to high solar activity, there is also a small chance of capturing them together with possible auroras.

Volcanoes, meteors, and climate change

Noctilucent clouds are formed by ice crystals attaching themselves to dust particles left at this altitude by meteor dust, volcanic eruptions (the high occurrence of NLCs in recent years was also caused by material from the Tonga volcanic eruption) or even human industrial activity. Ice at this altitude is mainly formed by the reaction of atmospheric oxygen with hydrogen under the influence of solar radiation or by the photochemical decomposition of methane. Last year, there was also speculation that their occurrence was due to the excessive number of rocket launches, particularly SpaceX's Falcon Heavy. However, this speculation has not yet been confirmed. Human industrial activity is certainly behind the occurrence of these clouds: NLCs began to appear significantly more frequently in the sky from 1885 onwards, i.e. during the industrial revolution. According to recent scientific studies (e.g. in Geophysical Research Letters), the higher occurrence of noctilucent clouds is also closely related to accelerating climate change.

Look out at dusk and dawn

Noctilucent clouds do not shine directly, but scatter radiation from the Sun located below the horizon. Since the clouds are located at an altitude of about 85 km, it is easy to calculate that the Sun must be about 6°-16° below the horizon, i.e. at a time when it is already deep twilight in our country. In our latitudes, we can see them in June and the first half of July between 10 p.m. and midnight, or in the morning between 2 a.m. and 4 a.m. (Central European Summer Time), always in the north, or between the northwest and northeast horizons. Their appearance can never be predicted in advance, so it is necessary to look in the directions where they may appear during this period and at the times mentioned above. It is also necessary to have the northern horizon as clear as possible.

First observations from Jeseník

This year's season of noctilucent clouds in the Czech Republic and Slovakia has already begun. The first successful observation was made by astronomer and photographer Pavel Klásek from Jeseník on Wednesday, June 4th, 2025, at around 3:35 a.m. Central European Summer Time. The clouds were visible for several tens of minutes that morning against a practically clear sky and were even visible to the naked eye. However, NLCs are not always prominent – sometimes only a camera can detect them. In recent years, however, there have been cases where NLCs appeared across virtually the entire sky above our territory and were so prominent that people could easily see them even from the centers of larger cities. Memorable cases occurred, for example, on June 21st, 2019, and July 5th, 2020. Detailed statistics on NLC observations over our territory, compiled by Tomáš Tržický of the Czech Astronomical Society, can be found on this website.

How not to lose them? On-line webcams can help

Since the occurrence of clouds is not certain every night, it is necessary to constantly look at the area around the northern horizon at the relevant times, or to watch webcams pointing in that direction. There are dozens of such cameras in the Czech Republic and Slovakia, usually belonging to hydrometeorological institutes, but also to private organizations (such as mountain resorts). If structures resembling NLCs appear on the cameras at the given times, i.e., between 10 p.m. and midnight or between 2 and 4 a.m., observers can react several tens of minutes in advance and go to observe the phenomenon with their own eyes (or photograph it). Those interested in not missing the phenomenon can register to receive notifications about NLC visibility on this page.

How to photograph the NLC?

Noctilucent clouds are easy to photograph. They are usually a fairly distinctive phenomenon, occurring at dusk or dawn when the sky is still relatively bright. It depends on how extensive the NLCs are in the sky. If they spread out like a thin veil low above the horizon, you will need a brighter lens and a camera on a tripod. In the case of really extensive clouds, a smartphone and panorama mode are often sufficient, as NLCs can spread over a large angular area from northwest to northeast. The most beautiful images are created when NLCs are composed with a beautiful terrestrial object – a calm water surface, city monuments, or perhaps a spreading tree. You can upload your observations to the gallery on the following website, where a long-term database of observations of this phenomenon is being created.

Contacts and further information:

Mgr. Petr Horálek

RNDr. Tomáš Gráf, Ph.D.