Astronomy Picture Of the Day (APOD)X-ray Transit of Mercury
This sequence of false color X-ray images captures a rare event - the passage or transit of planet Mercury in front of the Sun. Mercury's small disk is silhouetted against the bright background of X-rays from the hot Solar Corona.
NGC 1808: A Nearby Starburst Galaxy
NGC 1808 is a galaxy in turmoil. A barred spiral with marked similarities to our home Milky Way Galaxy, NGC 1808 is distinguished by a peculiar nucleus, an unusually warped disk, and strange flows of hydrogen gas out from the central regions.
The Universe Evolves
Scroll right and watch the universe evolve. Above is a computer simulation depicting the evolution of our entire universe. On the far left is a slice of the universe soon after the Big Bang - over 10 billion years ago.
Solar Magnetic Bananas
Is that our Sun? The unusual banana-shaped loops shown above are actually part of a computer-generated snap-shot of our Sun's magnetic field. This animated frame was constructed using data from the ground-based U.S. Solar Vector Magnetograph and the space-based Japanese X-Ray Telescope Yohkoh.
Comet Hale Bopp Over Val Parola Pass
In 1997, Comet Hale-Bopp became much brighter than any surrounding stars. It could be seen even over bright city lights. Out away from city lights, however, it put on quite a spectacular show. Here Comet Hale-Bopp was photographed last March above Val Parola Pass in the Dolomite mountains surrounding Cortina d'Ampezzo, Italy.
Neptune, the Solar System's outermost gas giant planet, is 30 times farther from the Sun than Earth. Twelve years after a 1977 launch, Voyager 2 flew by Neptune and found surprising activity on a planet that receives only 3 percent as much sunlight as Jupiter.
A Planet For Gliese 876
Centered in this unremarkable, 1/4 degree wide patch of sky in the constellation Aquarius is the star Gliese 876. Gliese 876 is smaller than the Sun, only about 1/3 as massive, and too faint to be seen without a telescope. But it is known to be one of the nearest stars, only 15 light-years distant.
NGC 4650A: Strange Galaxy and Dark Matter
This strangely distorted galaxy of stars is cataloged as NGC 4650A. It lies about 165 million light-years away in the southern constellation Centaurus. The complex system seems to have at least two parts, a flattened disk of stars with a dense, bright, central core and a sparse, sharply tilted ring of gas, dust and stars.
Sparkling Star May Indicate Galactic Composition
If a star in this photograph twinkled slightly, would anyone notice? Would anyone care? Astronomers with the MACHO Collaboration noticed one such twinkle just last week, and many members of the astronomical community now care.
A Slice Through an Artificial Universe
We live in the era of humanity when most of our Universe is being mapped. To help understand these maps, astronomers computationally estimate the appearance of several possible candidate universes, to which maps of the real Universe can be compared.