Ganymede is the largest moon in our solar system, larger even than the planets Pluto and Mercury. ... Ganymede's surface consists of two main types of terrain: old, dark polygonal units, and young, bright valleys and ridges (see figure 11 ). ... In a similar way, hitting a large block of ice with a hammer makes white marks. ... Ganymede as seen by Voyager 2. ... Because Voyager couldn't spot any large impact craters, scientists have concluded that the moon's surface is young. ... Moon . ... Europa . ...

... Active Region 1429, visible above.. Jupiter and Venus from Earth . ... The sunset conjunction of Jupiter and Venus was visible last week almost no matter where you lived on Earth. ... NGC 2683: Edge On Spiral Galaxy . ... Bright planets Venus and Jupiter are framed by the National Solar Observatory's McMath-Pierce Solar Telescope in this very astronomical scene. ... First and foremost in the wide-angle 12-hour exposure is the grand design spiral galaxy M81, the largest galaxy visible in the image. ...

Io ( "EYE oh" ) is the fifth of Jupiter 's known satellites and the third largest; it is the innermost of the Galilean moons. ... Discovered by Galileo and Marius in 1610. ... Io's surface is radically different from any other body in the solar system. ... The material erupting from Io's vents appears to be some form of sulfur or sulfur dioxide. ... Analysis of the Voyager images led scientists to believe that the lava flows on Io's surface were composed mostly of various compounds of molten sulfur. ...

... They had expected to see impact craters like those on the other terrestrial bodies and from their number per unit area to estimate the age of Io's surface. ... This may have been the most important single discovery of the Voyager missions; it was the first real proof that the interiors of other "terrestrial" bodies are actually hot and active. ... A nalysis of the Voyager images led scienties to believe that the lava flows on Io's surface were composed mostly of various compounds of molten sulfur. ...

... ESO is building what will be the World's largest optical telescope array, The Very Large Telescope (VLT). The VLT Project organisation is responsible for the design and construction of the Unit Telescopes, including enclosures, optics, adapter-rotators and coating unit. ... Unit Telescopes Overview - This page is outdated, an update is in process. ... Secondary mirror (M2 Unit) - This page is outdated, an update is in process. ... Coating Unit - This page is outdated, an update is in process. ...

... Tonight's Sky . ... The Magazine . ... Star Atlas . ... An artificial comet holds secrets to Earths life . ... Astronomy for Kids . ... Observing springtime deep-sky objects with a large telescope . ... The planet has extreme temperature swings and perhaps active lava flows. ... A digital supplement to Astronomy magazine. ... Join TravelQuest International with Astronomy and Discover magazines on one of three great tour options surrounding this celestial spectacle . ... Astronomy Magazine . ...

... More on 51 Peg: . The discovery of a Jupiter--mass planet in orbit around the solar--type star 51Peg has been reported by Michel Mayor and Didier Queloz (Geneva Observatory) on October 6th at the 9th Cambridge workshop on "cool stars, stellar systems, and the sun" held at Florence (Italy). ... Recall that the measurements of radial velocity only yield v sin i which in turn gives us M sin i. For most values of i, sin i will be greater than 0.5 and this gives a mass estimate of 0.5 Jupiter masses. ...

... Armagh Observatory, College Hill, Armagh BT61 9DG, +44 (0)28 3752 2928 . ... September Perseid meteors captured by the . ... Its occurrence provides astronomers with interesting new data about the hidden trails of meteoroids тАФ small bodies ranging in size from fine dust particles to objects of marble-size and larger тАФ in the solar system and their supposed sources: comets and asteroids passing through the inner solar system. ... The particular comet that created the September Perseids is unknown...

... The images that will be released over the next several days capture each of the 4 Galilean satellites in their orbits around the giant planet. This true color composite frame, made from narrow angle images taken on December 12, 2000 around 15 hours UTC (spacecraft event time) captures the innermost Galilean satellite, Io, and its shadow in transit again the disk of Jupiter. ... The image scale is 117 km/pixel. ... Credit: NASA/JPL/University of Arizona Released: December 20, 2000 ...

... A dynamo is created in a magnetic field by an electric circuit, part of which is moving relative to the rest (additional conditions must also be met). ... Furthermore, the plasma between them conducts electricity very well along its magnetic field lines, which act as if they were wires connecting Io and the planet (drawing). ... The drawing is not to scale. ... The Hubble Space Telescope , using its Wide Field and Planetary Camera 2, has been photographing auroras of the planet Jupiter. ...

by virtue of its high galactic latitude (+51 deg), low HI column density (2.2 x 10^20), high declination (increased visibility from KPNO), low IRAS 100 micron cirrus emission , and the absence of many bright stars or nearby rich clusters. Click here to see an ascii table of the 256 J2000 Survey Grid Coordinates . To access our I-band images: Click Here! To access the cluster catalog: Click Here! ... 2-pt Corr. ... 2002 - 2005 Marc Postman Last Updated: 28 April 2005 . ...

... 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. ...

Astronotes Armagh Planetarium's Stellar Blog! ... Solar System . ... Planets . ... This bizarrely shrunken planetary system was found by NASAтАЩs Kepler mission, hence the parent star has been named Kepler-11. ... Planetary scientist and Kepler science team member Jack Lissauer said ?These six planets are mixtures of rock and gases, possibly including water.тАЭ €аNone of these strange new worlds are likely to be home to any form of life; their surface conditions are simply too extreme. ...

... About ATNF overview . ... Australia Telescope Steering Committee . ... Murchison Radio-astronomy Observatory . ... Parkes radio telescope . ... Australia Telescope 20GHz Survey . ... Bright prospects: Comparing the H Survey with large-scale radio continuum emission . ... Prospects for comparisons between the AAO/UKST H \ survey and large-scale radio continuum emission are considered, with particular reference to the recently completed Parkes 2.4-GHz survey of the southern Galactic Plane. ...

LARGE-SCALE PHENOMENA AT THE SUN ASSOCIATED . WITH FILAMENT ERUPTIONS OUTSIDE ACTIVE . ... Considering the 12.09.1999 event as an example, we analyze manifestations of large-scale disturbances associated with coronal mass ejections (CMEs) caused by filament eruptions outside of active regions. ... The filament eruption occurred in relatively weak magnetic fields, but it was accompanied by larger-scale phenomena than flare events do. ...

... 739C As one part of a program to detect complete samples of active extragalactic objects, the 3.36x10^-3 sr field centered on alpha=12h04min, delta=+11deg30' (1950.0) was mapped with the Very Large Array at 1411MHz. Sixty-seven maps cover this field so that no point is more than 15arcmin from the nearest map center. ... The rms map noise is 0.030 + 0.001 mJy, and the resulting source list is complete to a map peak flux density S_p = 0.2 mJy within 25 arcmin of the field center. ...

... Today this year's largest group of sunspots will cross the Sun's central meridian. ... The next day, the number of spots in the group reached five, and the day after, on June 2nd, it was possible to count thirteen sunspots on solar disk, which had been clear prior to this. ... This year's two most powerful active areas, which passed across the solar disk at the beginning of May, 2009, are set to appear in the Sun's eastern sector in two days, on June 6th. ...

... Currently, there is very little information on comets which are active beyond the orbit of Jupiter. ... Previous observations conducted by our team with the SAO RAS 6-m telescope showed that some of these comets have extended tails dissimilar to the tails of comets forming at close heliocentric distances. ... We for the first time measured the linear polarization of scattered emission for the two distant comets C/2010 S1 (LINEAR) and C/2010 R1 (LINEAR) at heliocentric distances of 5.9-7.0 au. ...

The properties of the midplanes of planet-forming protostellar disks remain largely unprobed by observations due to the high optical depth of dust and commonly observed molecules. However, rotational emission lines from rare molecules may have optical depths near unity in the vertical direction, so that the lines are strong enough to be detected, yet remain transparent enough to trace the disk midplane. In this talk, I will present a chemical evolution model of an MRI-active T-Tauri disk. ...

... The Large Magellanic Cloud is a Dwarf Irregular galaxy in orbit around our own Milky Way. It is a large object, several degrees in size, and easily visible to the unaided eye in Southern Hemisphere skies. The LMC is located in the constellation of Doradus at about 5h30m Right Ascension, -68 degrees Declination, and lies at a distance of roughly 50 kiloparsecs (160,000 light years) from Earth. ...