Circumpolar Star Trails
18.01.2019

As Earth spins on its axis, the stars appear to rotate around an observatory in this well-composed image from the Canary Island of Tenerife. Of course, the colorful concentric arcs traced out by the stars are really centered on the planet's North Celestial Pole.

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.

Emission and Reflection in NGC 6559
23.10.2001

Bright gas and dark dust permeate the space between stars in a nebula known as NGC 6559. The gas, primarily hydrogen, is responsible for the diffuse red glow of the emission nebula. As energetic...

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.

A Passing Spaceship Views Earth
4.02.1998

This is how Earth appeared to the passing spacecraft NEAR. The Near Earth Asteroid Rendezvous (NEAR) spacecraft was launched from Florida, USA, planet Earth in 1996. After a quick flyby of asteroid Mathilde in June last year, NEAR passed the Earth two weeks ago on its way to asteroid 433 Eros.

Quasar in an Elliptical Galaxy
9.04.1998

Where do quasars live? Quasars are the brightest objects in the universe, so bright they can be seen from across the universe. Observations continue to show that most quasars are surrounded by a relatively faint nebulous patch. Astronomers are trying to identify the nature of these patches.

An Active Region of the Sun
16.06.1998

The Sun is a busy place. This false-color image depicts an active region near an edge of the Sun. Hot plasma is seen exploding off the Sun's photosphere and traveling along loops defined by the Sun's magnetic field.

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.

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.

NGC 4755: A Jewel Box of Stars
11.11.1996

The great variety of star colors in this open cluster underlie it's name: The Jewel Box. The bright central star Kappa Crucis is red, in contrast to the many blue stars that surround it. The cluster contains just over 100 stars, and might be no older than 10 million years.