Starlight Reflections
14.04.1998

Wisps of dust fill the space between the stars. This dust is usually invisible, subtly acting to dim the light of more distant stars. Sometimes this dust is thick and prominent as dark patches on otherwise bright emission nebulae. Other times this dust may show itself by reflecting the light of bright, nearby stars.

Hot Gas and Dark Matter
4.04.1999

Is the gravity of the galaxies seen in this image high enough to contain the glowing hot gas? Superposed on an optical picture of a group of galaxies is an image taken in X-ray light.

Ice Clouds over Mars
13.10.1997

Mars has clouds too. The above true color image taken in August by Mars Pathfinder shows clouds of ice high in the Martian atmosphere. Unlike Earth's atmosphere which is composed predominantly of nitrogen and oxygen, Mars' atmosphere is composed mostly of carbon dioxide.

NGC 1977: Blue Reflection Nebula in Orion
22.07.2001

The Orion Nebula is visible to the unaided eye as a fuzzy patch near the famous belt of three stars in the Orion. The above picture captures a part of the Orion Nebula that primarily reflects light from bright Orion stars.

Hot Gas and Dark Matter
2.09.1995

Is the gravity of the above galaxies high enough to contain the glowing hot gas? Superposed on an optical picture of a group of galaxies is an image taken in X-ray light. The X-ray...

Barsoom
31.03.2001

"Yes, I have been to Barsoom again ..." begins John Carter in Edgar Rice Burroughs' 1913 science fiction classic "The Gods of Mars". In Burroughs' novels describing Carter's adventures on Mars, "Barsoom" is the local inhabitants' name for the Red Planet. Long after Burroughs' stories were published, Mars continues to inspire Earthdwellers' interests and imagination.

Io's Active Volcanoes
27.10.1996

Why is Io green at night? In this just-released nighttime picture of Jupiter's moon Io, the red spots clearly show Io's current volcanically active regions. But what is causing the global green sheen? This telling picture was taken by the automated Galileo spacecraft currently orbiting Jupiter while Io was in Jupiter's shadow.

Our Dusty Universe
21.01.1998

What's black & white and red all over? Add our universe to this list. Adrift in a vast sea of darkness are not only familiar bright stars but dust that glows predominantly in far-infrared light.

Our Dusty Universe
19.11.2000

What's black & white and red all over? Add our universe to this list. Adrift in a vast sea of darkness are not only familiar bright stars but dust that glows predominantly in far-infrared light.

APOD: 2008 January 1- Rays from an Unexpected Aurora
1.01.2008

This aurora was a bit of a surprise. For starters, on this day in 2002, no intense auroral activity was expected at all. Possibly more surprising, however, the aurora appeared to show an usual structure of green rays from some locations.