The Winter Hexagon
6.11.2002

Some of the brightest stars form a large and easily found pattern in the winter sky of Earth's northern hemisphere. Dubbed the Winter Hexagon, the stars involved can usually be identified even in the bright night skies of a big city.

Sizzling Io
6.07.1998

What's cooking on Io? This active moon of Jupiter is marked with volcanoes spewing lava that is now known to be hotter than any lava on Earth. Above is the highest resolution color-enhanced image yet composed of the most active surface in our Solar System. Features as small as three kilometers are visible.

A Sun Pillar
13.03.2001

Have you ever seen a sun pillar? When the air is cold and the Sun is rising or setting, falling ice crystals can reflect sunlight and create an unusual column of light. Ice sometimes forms flat, stop-sign shaped crystals as it falls from high-level clouds.

Neptune's Moon Proteus
4.11.1995

Proteus is the second largest moon of Neptune behind the mysterious Triton. Proteus was discovered only in 1982 by the Voyager 2 spacecraft. This is unusual since Neptune has a smaller moon - Nereid - which was discovered 33 years earlier from Earth.

A Pileus Iridescent Cloud Over Ethiopia
24.08.2011

Yes, but how many dark clouds have a multicolored lining? Pictured, behind this darker cloud, is a pileus iridescent cloud, a group of water droplets that have a uniformly similar size and so together diffract different colors of sunlight by different amounts.

The Sky Towards Sagittarius
7.09.1998

A variety of stars and nebulae can be found towards the constellation of Sagittarius. Dense fields of stars laced with dark lanes of dust crowd this region only a few degrees from the center of our Galaxy.

Symbiotic Star System R Aquarii
4.01.1996

Sometimes stars work together to create a spectacular display. Such is the case with the binary star system R Aquarii - a "symbiotic" star system. Here two stars, a variable giant and a white dwarf companion - create both a nebula and a jet.

Central Galactic Star Bursts
1.10.1995

The pictured core of the galaxy NGC 253 shows an exceptionally high rate of star formation. In the center are some of the densest knots of stars ever found, surrounded by glowing gas and dust lanes. Galaxies where such high star formation rates are seen are called "starburst" galaxies.

Mercury's Faults
21.01.1996

The surface of the planet Mercury is not without fault. In this case, however, "fault" refers to unusual surface features that are the topic of much speculation. The above fault line is called Santa Maria Rupes, and runs through many prominent craters.

Dark Bok Globules in IC 2944
6.10.1995

The dark spots in the above picture are not photographic defects but an unusual type of interstellar cloud known as a Bok globule. Bok globules, named after astronomer Bart Bok who studied them extensively, are small dark clouds made of gas and dust that are typically condensing to form a star or stars.