Astronomy Picture Of the Day (APOD)The Double Nucleus of M31
The center of M31 is twice as unusual as previously thought. In 1991 the Planetary Camera then onboard the Hubble Space Telescope pointed toward the center of our Milky Way's closest major galactic neighbor: Andromeda (M31). To everyone's surprise, M31's nucleus showed a double structure.
Triton: Neptune's Largest Moon
Today marks the 150th anniversary of the discovery of Triton. On October 10 1846, William Lassell was observing the newly discovered planet Neptune. He was attempting to confirm his observation, made just the previous week, that Neptune had a ring. But this time he discovered that Neptune had a satellite as well.
M31: The Andromeda Galaxy
Andromeda is the nearest major galaxy to our own Milky Way Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the hundreds of billions of stars that compose it.
ROSAT Explores The X-Ray Sky
Launched in 1990, the orbiting ROSAT observatory explored the Universe by viewing the entire sky in x-rays - photons with about 1,000 times more energy than visible light. This ROSAT survey produced the sharpest, most sensitive image of the x-ray sky to date.
Caught in the act earlier this summer by the Hubble Space Telescope, the volcanic moon Io (above and right of center) and its shadow (black dot) are seen here against Jupiter's clouds.
A Crescent Earth At Midnight
The Earth's northern hemisphere appears outlined as a sunlit crescent in this dramatic view from the GOES 8 satellite. The image was made near midnight for the Geostationary Operational Environmental Satellite on June 22 this year, two days after the Summer Solstice.
A Close-Up of the Horsehead Nebula
1500 light years away lies a nebula of quite peculiar shape. How did the dark dust cloud shown above come to be shaped like a horse's head? Nobody knows! Barnard 33, as this...
Globular Cluster Omega Centauri
Does an old, red globular cluster have any hot, blue stars? The rightmost picture, taken by the Ultraviolet Imaging Telescope in ultraviolet light, shows that indeed it does. Pictured, Omega Centauri is the largest known globular cluster in our Galaxy, containing well over a million stars.
Three Views of Jupiter's Io
The Galileo spacecraft orbiting Jupiter continues to return impressive results. The Galileo team has just released three more photographs of Jupiter's volcanic moon Io taken in June. These three photos are reflected at the bottom of the above picture, digitally enhanced to better show important features.
Orion's Horsehead Nebula
The Horsehead Nebula is arguably the most famous nebula on the sky. It is visible as the black indentation to the red emission nebula seen just to the right of center of the above photograph. The bright star near the center is located in the belt of the familiar constellation of Orion.