Noctilucent cloud

Some clouds glow at night.

These clouds are very high up. They are made of tiny ice crystals. They form when it is very cold. This happens near the top of our air.

You can see them during the summer. They glow because the sun hits them. The ground is in the dark, but the clouds are in the light. They look like bright streaks in the sky.

They are beautiful to see.

Some clouds glow in the dark sky. We call them noctilucent clouds. The name means "night shining" in Latin.

These clouds are very high up. They live in the mesosphere. This is the part of our air just below space. They are made of tiny ice crystals. These crystals are very small. They form when it is extremely cold.

To make these clouds, you need three things. You need water vapor, dust, and cold air. The dust might come from tiny space rocks called micrometeors.

These clouds mostly appear during the summer. This sounds strange because summer is usually warm. But the mesosphere is coldest during the summer. This happens because of how winds move the air. You can only see them when the sun is low. The ground is in shadow, but the high clouds still hit the sunlight.

Scientists use satellites to study them. These tools help us see how they change.

Noctilucent clouds are very special clouds in our sky. Their name comes from Latin words meaning "night shining."

These clouds are the highest in Earth's atmosphere. They live in a layer called the mesosphere. This layer is about 80 kilometers above the ground. From space, scientists call them polar mesospheric clouds. They look like thin, glowing layers of light. You can only see them during astronomical twilight. This happens when the ground is in shadow. The sun is low, but it still hits these high clouds.

These clouds form through a very specific way it works. They need three things: water vapor, dust, and extreme cold. The tiny ice crystals are only 100 nanometers wide. Most clouds form when water hits particles in the air. These clouds can form directly from water vapor. The dust might come from micrometeors hitting our atmosphere. It could also come from volcanoes or dust from lower air. The mesosphere is extremely thin and dry. It has only one hundred millionth the moisture of the Sahara. Because it is so dry, it must be below -130 degrees Celsius.

People first noticed these clouds in 1885. This was two years after the Krakatoa volcano erupted. Some thought the clouds were just volcanic ash. However, the clouds stayed even after the ash fell. A scientist named Malzev proved they were not dust in 1926. Otto Jesse was the first to photograph them in 1887. He is also the person who gave them their name. He noticed them while studying strange sunsets from the volcano. Later, a scientist named Wegener suggested they were made of ice. He was right about the ice crystals.

Scientists use many tools to study these clouds today. The OGO-6 satellite first saw them from space in 1972. Later, the AIM satellite was launched on April 25, 2007. It was the first satellite just for these clouds. It began its work on May 25, 2007. Researchers also use radar to see them. These clouds reflect radar waves very well. Some think this happens because of metal films on the ice. These films might be made of sodium and iron. These atoms come from micrometeors in space.

These clouds are linked to many things we know. We see regular clouds in our lower sky every day. Noctilucent clouds have four main shapes. Some look like thin veils or long bands. Others look like billows or even spinning whirls.

We can even see similar clouds on Mars. Those clouds are made of carbon dioxide crystals. Humans have even made artificial clouds with rockets. In 2018, a NASA rocket released water canisters. This helped scientists study how the clouds work. It is a wonderful way to learn about our atmosphere.

Noctilucent clouds, often called night-shining clouds, are unique phenomena found in the upper reaches of our atmosphere.

These clouds exist in the mesosphere, which is the layer of air above the stratosphere. From the perspective of a satellite in space, scientists refer to them as polar mesospheric clouds (PMCs). They appear as diffuse, glowing layers of water ice crystals. These clouds are significant because they are the highest clouds in Earth's atmosphere. They are only visible from the ground during astronomical twilight. This occurs when the observer is in Earth's shadow, but the high-altitude clouds are still illuminated by sunlight.

The formation of these clouds requires a very specific set of conditions. They need water vapor, dust particles, and extremely cold temperatures to exist. The clouds are composed of tiny water ice crystals, measuring up to 100 nanometers in diameter. While most clouds form when water collects on existing particles, these mesospheric clouds can also form directly from water vapor. The source of the necessary dust is believed to come from micrometeors, though volcanic particles or tropospheric dust are also possibilities. Water vapor can reach this height through gaps in the tropopause or via chemical reactions involving methane and hydroxyl radicals.

Temperature plays a vital role in where and when these clouds appear. The mesosphere is incredibly dry, containing only about one hundred millionth the moisture found in the air of the Sahara Desert. Because the air is so thin and dry, ice crystals can only form at temperatures below approximately -130 degrees Celsius. Interestingly, these clouds are most common during the summer months. This happens because of seasonally varying vertical winds. These winds cause upwelling, which leads to adiabatic cooling in the summer. This process makes the summer mesosphere much colder than the winter mesosphere.

Humanity's history with these clouds began with significant scientific debate. They were first recorded in 1885, shortly after the 1883 eruption of the Krakatoa volcano. Many people originally thought the clouds were simply volcanic ash. However, the clouds remained even after the volcanic debris settled. In 1926, a scientist named Malzev proved they were not made of volcanic dust. Otto Jesse was a key figure in their study. He was the first to photograph them in 1887 and is credited with coining the term "noctilucent."

Modern technology has allowed us to map these clouds with great precision. The OGO-6 satellite provided the first space-based detection in 1972. Later, the Solar Mesosphere Explorer mapped their distribution between 1981 and 1986. A major milestone occurred on April 25, 2007, with the launch of the AIM satellite. The Aeronomy of Ice in the Mesosphere (AIM) satellite was the first mission dedicated entirely to studying these clouds.

Scientists have even used rockets to create artificial clouds. In 2018, a NASA rocket released water-filled canisters at an altitude of 80 kilometers to study the phenomenon.

Noctilucent clouds exhibit several distinct physical structures. Scientists categorize them into four main types. Type I clouds are called veils; they are very thin and lack a clear shape. Type II clouds appear as long, parallel bands. Type III clouds are known as billows, which look like short, parallel streaks. Finally, Type IV clouds are called whirls, which form partial or complete rings with dark centers.

These structures help researchers understand the complex dynamics of the upper atmosphere.

There are also fascinating connections between these clouds and other scientific fields. For example, noctilucent clouds show high radar reflectivity in frequencies between 50 MHz and 1.3 GHz. Some researchers suggest this happens because ice grains are coated in a thin metal film of sodium and iron. These metals are stripped from incoming micrometeors and settle near the clouds. Furthermore, these clouds share similarities with phenomena on other planets. In 2008, the Mars Express mission discovered carbon dioxide-crystal clouds on Mars. Like Earth's noctilucent clouds, these Martian clouds can only be seen when the Sun is below the horizon.