... Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. December 20, 1999 . Lava Fountain on Jupiter's Io . Credit: Galileo Project , SSI , University of Arizona , JPL , NASA . ... The robot Galileo spacecraft orbiting Jupiter photographed the volcanic eruption during its close flyby of the moon late last month . ... About APOD > . ... NASA Technical Rep.: ... A service of: LHEA at NASA / GSFC . ...

... Jupiter's Rings . ... Unlike Saturn's bright rings which are composed of chunks of rock and ice, Jupiter's rings appear to consist of fine particles of dust. ... Exploring Saturn's Rings . ... By watching a star flicker and fade as it passed behind Saturn's rings, NASA's Voyager 2 spacecraft was able explore the ring system in amazing detail. ... Saturn's spectacular system of bright rings has been the subject of study and wonder since Galileo first turned his telescope on the ringed planet in 1610....

... Galileo Probe . The Galileo spacecraft was designed to study Jupiter's atmosphere, satellites, and surrounding magnetosphere for two years. ... From there, Galileo will spend more than five years traveling to Jupiter, where it will become the first spacecraft to make direct measurements from an instrumented probe within Jupiter's atmosphere. ... This image, taken by the Hubble Space Telescope, shows the predicted site at which the Galileo Probe will enter Jupiter's atmosphere on December 7, 1995. ...

... Jupiter Eyes Ganymede . Credit: Cassini Team , U. Arizona , JPL , NASA . ... This moon, visible on the lower right, is Ganymede , and the planet it orbits, Jupiter , seems to be keeping a watchful eye, as its Great Red Spot appears serendipitously nearby. This recently released enhanced-contrast image from the robot spacecraft Cassini captures new details of the incredible intricacies of Jupiter's complex cloud patterns. ... Tomorrow's picture: Manicouagan Impact Crater . ...

... Bad Astronomy . ... Bitesize Astronomy . ... Last week's Snack talked about how black holes can affect the environment around them in such a way as to be very bright . ... It's a common misconception that black holes always have matter swirling into them. ... As this matter gets closer and closer to the black hole it piles up and a large, fairly flat disk forms. This is called the accretion disk , because matter from this disk accretes (that is, falls in) on the black hole. ... 2008 Phil Plait. ...

... Armagh Observatory, College Hill, Armagh BT61 9DG, +44 (0)28 3752 2928 . ... Although the comet itself never comes dangerously close to the Earth, the particles of dust that it has shed during its many past passages through perihelion found their way into the Earth's atmosphere, appearing as meteors in the cold December sky. ... Animation 1 . ... An Ursid meteor captured by the Armagh Observatory's NE-facing meteor camera in the early morning of 23rd December. ... Meteor Showers Online . ...

M1 image More About M1 Nice Color Picture . ... M16 image More About M16 HST image . ... M31 image More About M31 Nice Color Picture . ... M42 image ; M43 image More About M42/43 Nice Color CCD Picture . M51 image More About M51 Color Image of M51 M51 Supernova . M57 image More About M57 Nice Color CCD Picture Very Deep M57 Image . ... M81 image More About M81 M81 Supernova Ultraviolet Image of M81 More about Ultraviolet Imaging . M82 image More About M82 M82 False Color M82 True Color . ...

... In summer 1994, the biggest news in astronomy was the collision of comet Shoemaker-Levy 9 with Jupiter. During this school year, Jupiter will charge back into the limelight with the arrival of the Galileo spacecraft (see figure 8 ). On Dec. 7, following a tortuous six-year ramble through the solar system, Galileo will begin its two-year mission studying Jupiter and its gaggle of moons. ... Besides the camera, Galileo will carry instruments capable of identifying minerals on Jupiter's moons. ...

Astronotes Armagh Planetarium's Stellar Blog! ... Earth Satellites . ... Sadly C/ 2014 Q2 will probably not be as spectacular a sight as Comet C/ 2011 W3 (Lovejoy), visible near Earth?s horizon in this nighttime image from the International Space Station on 22 December 2011. ... The comet made its closest approach to Earth on 7€а January 2015, at a distance of 72 million km (45 million miles).€а In January the comet will race though the constellations Eridanus, Taurus, Aries and Triangulum. ...

Image credit: Michael Nolan, Arecibo Observatory. These radar images of near-Earth asteroid 2001 SN263 were obtained on 2008 Feb 12 and 13. ... Image from Feb 12 . ... First near-Earth triple asteroid discovered by Arecibo Observatory . ... was discovered this week by astronomers at the sensitive radar telescope at Cornell University?s Arecibo Observatory in Puerto Rico. ... For example, Arecibo has discovered more than half of the near-Earth binary asteroid systems discovered since 1999. ...

Supernova 2009js in NGC 918 . This page is devoted to information on Supernova 2009js in NGC 918 . Basic information on this SN, including the last reported brightness, on this Supernova can be found on the main page . Information on the original web pages for many of these images can be found on the updates and links web pages. Discovered independently by Lick Observatory Supernova Search (USA) and Koichi Itagaki (Japan). ... 2009/10/11.44 . 17.2 . ... Joseph Brimacombe . ...

... Tonight's Sky . ... Observing . ... Sky this Month . ... Astronomy for Kids . ... Can you explain Mercury's retrograde motion? Do other planets appear to do this also? ... When astronomers talk about retrograde motion, generally they refer to the apparent motion outer planets make as Earth passes them while orbiting the Sun. ... Get instant access to subscriber content on Astronomy.com! ... Receive news, sky-event information, observing tips, and more from Astronomy's weekly email newsletter. ...