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Astronomy portal

Astronomy (Greek: αστρονομία = άστρον + νόμος, astronomia = astron + nomos, literally "law of the stars") is the study of the evolution and physical and chemical properties of celestial objects. Astronomical observations are not only relevant for astronomy as such, but provide essential information for the verification of fundamental theories in physics, such as the general relativity theory. Complementary to observational astronomy, theoretical astrophysics seeks to explain astronomical phenomena.

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Article of the month

Callisto (pronounced /kəˈlɪstoʊ/ kə-LIS-toe, or as Greek Καλλιστώ) is a moon of the planet Jupiter, discovered in 1610 by Galileo Galilei.[1] It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about 1,880,000 kilometers.[2] It does not form part of the orbital resonance that affects three inner Galilean satellites—Io, Europa and Ganymede—and thus does not experience appreciable tidal heating.[3] Callisto rotates synchronously with its orbital period, so the same face is always turned toward Jupiter. Callisto's surface is less affected by Jupiter's magnetosphere than the other inner satellites because it orbits further away.[4]

Callisto is composed of approximately equal amounts of rock and ices, with a mean density of about 1.83 g/cm3. Compounds detected spectrally on the surface include water ice, carbon dioxide, silicates, and organics. Investigation by the Galileo spacecraft revealed that Callisto may have a small silicate core and possibly a subsurface ocean of liquid water at depths greater than 100 kilometers.[5][6]

Recently featured: IK Pegasi – Comet – Supernova

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Did you know

...that Zeeman-Doppler imaging is a technique used to map the surface magnetic field of stars?

...that Astronomische Nachrichten, founded by H. C. Schumacher in 1821, is the world's oldest extant astronomical journal?

...that the Stingray Nebula, thought to have formed around 1987, is the youngest known planetary nebula?

...that the Mark II radio telescope built in 1964 at Jodrell Bank Observatory, UK was the first ever telescope to be controlled by a digital computer?

...that Comet Shoemaker-Levy 9 passed within Jupiter's Roche limit in 1992, causing it to break up into smaller pieces two years before it collided with the planet?

...that the Kaidun meteorite fell on March 12, 1980 on a Soviet military base in Yemen and may be from Phobos?

...that Pluto is now considered the largest member of the Kuiper belt after its retirement as the 9th planet?

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Picture of the week

This is a composite image of N49, the brightest supernova remnant in optical light in the Large Magellanic Cloud. The Chandra X-ray Observatory image (blue) shows million-degree gas in the center. Much cooler gas at the outer parts of the remnant is seen in the infrared image from Spitzer Space Telescope (red). While astronomers expected that dust particles were generating most of the infrared emission, the study of this object indicates that much of the infrared is instead generated in heated gas.

The unique filamentary structure seen in the optical image by Hubble Space Telescope (white & yellow) has long set N49 apart from other well understood supernova remnants, as most supernova remnants appear roughly circular in visible light. Recent mapping of molecular clouds suggests that this supernova remnant is expanding into a denser region to the southeast, which would cause its asymmetrical appearance. This idea is confirmed by the Chandra data. Although X-rays reveal a round shell of emission, the X-rays also show brightening in the southeast, confirming the idea of colliding material in that area.

X-ray: NASA/CXC/Caltech/S.Kulkarni et al.; Optical: NASA/STScI/UIUC/Y.H.Chu & R.Williams et al.; IR: NASA/JPL-Caltech/R.Gehrz et al.

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Astronomy News

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Astronomical events in June 2008

All times UT unless otherwise specified.

3 June Moonat perigee3 June, 19:23 New moon10 June, 15:04 Moon at First quarter16 June Moon at apogee18 June, 17:30 Full moon26 June, 12:10 Moon at Third quarter edit