The Trail of the Intruder
24.02.1997

In yesterday's episode our hero, the Cartwheel galaxy, had survived a chance cosmic collision with a small intruder galaxy - triggering an expanding ring of star formation. Hot on the intruder's trail, a team of multiwavelength sleuths have compiled evidence tracking the reckless galaxy fleeing the scene.

Venus at the Edge
9.06.2012

As its June 6 2012 transit begins Earth's sister planet crosses the edge of the Sun in this stunning view from the Hinode spacecraft. The timing of limb crossings during the rare transits was used historically to triangulate the distance to Venus and determine a value for the Earth-Sun distance called the astronomical unit.

Light Pillars from a Little Planet
31.01.2014

Eerie pillars of light ring the edges of this snowy little planet. Of course the little planet is planet Earth, shown in a nadir-to-zenith, around-the-horizon, little planet projection. The spherical panoramic image mosaic maps a view from Siilinjärvi in eastern Finland.

Uranus's Moon Umbriel: A Mysterious Dark World
7.04.1996

Why is Umbriel so dark? This dark moon reflects only half the light of other Uranus' moons such as Ariel. And what is that bright ring at the top? Unfortunately, nobody yet knows. These questions presented themselves when Voyager 2 passed this satellite of Uranus in January 1986.

Jupiters Moons Thebe, Amalthea, and Metis
8.05.2000

The robot spacecraft Galileo in orbit around Jupiter has recently photographed the inner moons of Jupiter in greater detail than ever before. These pictures of Thebe, Amalthea, and Metis are shown to scale, and reveal details as small as three kilometers across. Amalthea, by contrast, has a total length of about 200 kilometers.

Identify this Phenomenon
13.09.2004

What caused this ring of colors? At the time of this writing, MIT Physics Professor Walter Lewin had yet to find someone who can give the correct explanation. Not students. Not colleagues. Not APOD editors. He wonders how the astute readers of APOD will do. Can you match wits with Professor Lewin?

The Swirling Storms of Saturn
10.10.2005

Storms larger than hurricanes continually dot the upper atmosphere of the planet Saturn. A view of many storms occurring simultaneously was captured in July by the robot Cassini spacecraft now orbiting Saturn. An image of unusually high detail was made possible at that time when Cassini isolated a very specific color of polarized infrared light.

One Armed Spiral Galaxy NGC 4725
6.06.2009

While most spiral galaxies, including our own Milky Way, have two or more spiral arms, NGC 4725 seems to have only one. In this sharp color image, the solo spira mirabilis is tightly wound, traced by bluish, newborn star clusters.

Aurora at Midnight
5.05.1998

What's happening behind those trees? Aurora. This picture was taken at midnight near Fairbanks, Alaska, and captures familiar trees, common clouds, and a glowing sky markedly different than a sunset. Particularly strange is the green auroral ring caused by ionized oxygen high in the Earth's atmosphere.

NGC 3132: The Eight Burst Nebula
10.11.1998

It's the dim star, not the bright one, near the center of NGC 3132 that created this odd but beautiful planetary nebula. Nicknamed the Eight-Burst Nebula and the Southern Ring Nebula, the glowing gas originated in the outer layers of a star like our Sun.