A Retreating Thunderstorm at Sunset
28.08.2013

What type of cloud is that? This retreating cumulonimbus cloud, more commonly called a thundercloud, is somewhat unusual as it contains the unusual bumpiness of a mammatus cloud on the near end, while simultaneously producing falling rain on the far end.

A Retreating Thunderstorm at Sunset
16.01.2022

What type of cloud is that? This retreating cumulonimbus cloud, more commonly called a thundercloud, is somewhat unusual as it contains the unusual bumpiness of a mammatus cloud on the near end, while simultaneously producing falling rain on the far end.

Methone: Smooth Egg Moon of Saturn
6.11.2012

Why is this moon shaped like a smooth egg? The robotic Cassini spacecraft completed the first flyby ever of Saturn's small moon Methone in May and discovered that the moon has no obvious craters.

GRB 060218: A Mysterious Transient
27.02.2006

What is it? Something is happening in a small portion of the sky toward the constellation of Aries and telescopes around the globe are tracking an unusual transient there as it changes day by day. No one is sure what it will do next.

Rocket, Meteor, and Milky Way over Thailand
12.02.2014

Can the night sky appear both serene and surreal? Perhaps classifiable as serene in the above panoramic image taken last Friday are the faint lights of small towns glowing across a dark foreground landscape of Doi Inthanon National Park in Thailand, as well as the numerous stars glowing across a dark background starscape.

APOD: 2017 November 22 Oumuamua: Interstellar Asteroid
22.11.2017

Nothing like it has ever been seen before. The unusual space rock 'Oumuamua is so intriguing mainly because it is the first asteroid ever detected from outside our Solar System -- although likely many more are to follow given modern computer-driven sky monitoring.

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.

Plane Contrail and Sun Halo
4.04.2017

What's happened to the sky? Several common features of the daytime sky are interacting in uncommon ways. First, well behind the silhouetted hills, is the typically bright Sun. In front...

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.

Methuselah Outcrop on Mars
2.05.2005

What the history of the outcropping of rock called Methuselah? The unusual rock group is visible on the left of the above image taken by the robot Spirit rover current exploring Mars. Methuselah was discovered while maneuvering over hilly terrain and shows unusual multiple layering that caught the attention of the rover science team.