Mammatus Clouds Over Saskatchewan
17.10.2015

Why is this cloud so bubbly? Normally, cloud bottoms are flat. The flatness is caused by moist warm air that rises and cools and so condenses into water droplets at a specific temperature, which usually corresponds to a very specific height. As water droplets grow, an opaque cloud forms.

Clouds Near the Edge of Space
22.08.2012

Noctilucent or night-shining clouds lie near the edge of space. From about 80 kilometers above Earth's surface, the icy clouds can still reflect sunlight even though the Sun itself is below the horizon as seen from the ground.

Io's Sodium Cloud
28.04.1997

Io has its own cloud. Jupiter's most active moon is visible on the left of the above false-color photograph, with its left side illuminated by sunlight. But what is happening on Io's right side? Here a plume of gas from the active volcano Prometheus also reflects sunlight.

Aurora Over Clouds
10.09.2003

Aurorae usually occur high above the clouds. The auroral glow is created when fast-moving particles ejected from the Sun impact air molecules high in the Earth's atmosphere. An oxygen molecule, for example, will glow in a green light when reacquiring an electron lost during a collision with a solar particle.

Noctilucent Clouds over Paris
11.07.2022

It's northern noctilucent cloud season. Composed of small ice crystals forming only during specific conditions in the upper atmosphere, noctilucent clouds may become visible at sunset during late summer when illuminated by sunlight from below. Noctilucent clouds are the highest clouds known and now established to be polar mesospheric clouds observed from the ground.

APOD: 2025 July 12 Б Clouds and the Golden Moon
11.07.2025

As the Sun set, a bright Full Moon rose on July 10. Its golden light illuminates clouds drifting through southern hemisphere skies in this well-composed telephoto image from Conceiццёo do Coitц, Bahia, Brazil. The brightest lunar phase is captured here with both a short and long exposure.

Lenticular Clouds Over Washington
4.11.2012

Are those UFOs near that mountain? No -- they are multilayered lenticular clouds. Moist air forced to flow upward around mountain tops can create lenticular clouds. Water droplets condense from moist air cooled below the dew point, and clouds are opaque groups of water droplets.

APOD: 2023 February 12 Б Mammatus Clouds over Nebraska
11.02.2023

When do cloud bottoms appear like bubbles? Normally, cloud bottoms are flat. This is because moist warm air that rises and cools will condense into water droplets at a specific temperature, which usually corresponds to a very specific height. As water droplets grow, an opaque cloud forms.

Unusual Clouds over Hong Kong
1.03.2016

What's that in the sky? Earlier this month, in the sky high above Hong Kong, China, not just one unusual type of cloud appeared -- but two. In the foreground was a long lenticular cloud, a cloud that forms near mountains from uprising air and might appear to some as an alien spaceship.

Noctilucent Clouds
15.06.2003

Sometimes it's night on the ground but day in the air. As the Earth rotates to eclipse the Sun, sunset rises up from the ground. Therefore, at sunset on the ground, sunlight still shines on clouds above.