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.

Callisto Enhanced
12.05.1998

Callisto is half rock and half ice. This moon of Jupiter is approximately the size of the planet Mercury, making it the third largest moon in the Solar System, after Ganymede and Titan. Callisto...

A Blue Moon Halo over Antarctica
10.08.2015

Have you ever seen a halo around the Moon? Such 22 degree rings around the Moon -- caused by ice crystals falling in the Earth's atmosphere -- are somewhat rare. OK, but have you ever seen a blue moon?

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.

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.

Reflections of Venus and Moon
18.05.2018

Posing near the western horizon, a brilliant evening star and slender young crescent shared reflections in a calm sea last Thursday after sunset. Recorded in this snapshot from the Atlantic beach at Santa Marinella...

Crater Copernicus
9.09.1998

One of the more prominent craters on the Moon is named Copernicus. Copernicus is a large young crater visible with binoculars slightly northwest of the center of the Moon's Earth-facing hemisphere. Copernicus is distinguished by its size and by the many bright rays pointing out from it.

Saturn's Moon Tethys
23.11.1995

Tethys is one of the larger and closer moons of Saturn. It was visited by both Voyager spacecraft - Voyager 1 in November 1980 and by Voyager 2 in August 1981. Tethys is now known to be composed almost completely of water ice. Tethys shows a large impact crater that nearly circles the planet.

A Big Dish at the VLA Radio Observatory
28.11.2006

They are so large, they are almost unreal. The radio dishes of the Very Large Array (VLA) of radio telescopes might appear to some as a strange combination of a dinosaur skeleton and common satellite-TV receiving dish.

Stars and Planets in the Halo of the Moon
20.03.2003

Photographed on March 13th from Caledon, Ontario, Canada, a bright Moon was surrounded by this lovely halo. Planet Jupiter and stars Procyon, Castor, and Pollux also appear within the circle of lunar light. Castor...