Ganymede: The Largest Moon in the Solar System
20.06.2000

If Ganymede orbited the Sun, it would be considered a planet. The reason is that Jupiter's moon Ganymede is not only the largest moon in the Solar System, it is larger than planets Mercury and Pluto.

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.

Aurora Over Iowa
18.12.2006

Last Thursday evening, stars were not the only lights in Iowa skies. Spectacular northern lights also shone from the heavens, extending across the midwestern USA and other locations not often graced with auroral displays.

Looking Back at an Eclipsed Earth
2.01.2011

Here is what the Earth looks like during a solar eclipse. The shadow of the Moon can be seen darkening part of Earth. This shadow moved across the Earth at nearly 2000 kilometers per hour.

Unusual Clouds over Hong Kong
2.03.2016

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.

Plane Crossing a Crescent Moon
12.02.2019

No, this is not a good way to get to the Moon. What is pictured is a chance superposition of an airplane and the Moon. The contrail would normally appear white, but the large volume of air toward the setting Sun preferentially knocks away blue light, giving the reflected trail a bright red hue.

A Circumhorizontal Arc Over Ohio
19.05.2019

Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon.

A Halo Around the Moon
15.05.2000

Have you ever seen a halo around the Moon? This fairly common sight occurs when high thin clouds containing millions of tiny ice crystals cover much of the sky. Each ice crystal acts like a miniature lens.

Eclipse City
20.08.2009

During July 22nd's solar eclipse, the Moon's dark shadow traced a narrow path as it raced eastward across India and China and on into the Pacific. Hong Kong was south...

Centaurus A
13.03.2010

Only 11 million light-years away, Centaurus A is the closest active galaxy to planet Earth. Spanning over 60,000 light-years, the peculiar elliptical galaxy, also known as NGC 5128, is featured in this sharp color image.