原帖由 bg3hb 于 2008-7-1 09:02 发表
的确,"千米"一词不论念还是听都不如“公里”来的爽。
拜读了。又学来一点知识。
老板今后何不多发一些天文方面的英文短文,让我等菜鸟学习外语的同时又学了知识。
不要太长。 ...
SOHO discovers its 1500th comet
27 June 2008
TheESA/NASA SOHO spacecraft has just discovered its 1500th comet, makingit more successful than all other comet discoverers throughout historyput together. Not bad for a spacecraft that was designed as a solarphysics mission.
SOHO’s record-breaking discovery was made on25 June. The small and faint Kreutz-group comet was discovered byUS-based veteran comet hunter and amateur astronomer Rob Matson.
Kreutz-group comets, or sungrazing comets have been observed formany hundreds of years. They travel very close to the Sun (if they wereto hit it, they would become 'sunstrikers'), with perihelion distanceless than 0.01 Astronomical Units (the mean distance between the Earthand the Sun), or some 1460000 km.
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| SOHO's recording-breaking discovery
| Whenit comes to comet catching, the SOlar and Heliospheric Observatory hasone big advantage over everybody else: its location. Situated betweenthe Sun and Earth, it has a privileged view of a region of space thatcan rarely be seen from Earth. From the surface, we can see regionsclose to the Sun clearly only during an eclipse.
Roughly 85% of SOHO discoveries are fragments from a once-greatcomet that split apart in a death plunge around the Sun, probably manycenturies ago. The fragments are known as the Kreutz group and now passwithin 1.5 million km of the Sun’s surface when they return from deepspace.
At this proximity, which is a near miss in celestial terms, most ofthe fragments are finally destroyed, evaporated by the Sun’s fearsomeradiation – within sight of SOHO’s electronic eyes. The images arecaptured by the Large Angle and Spectrometric Coronograph (LASCO), oneof 12 instruments on board.
Ofcourse, LASCO itself does not make the detections; that task falls toan open group of highly-skilled volunteers who scan the data as soon asit is downloaded to Earth. Once SOHO transmits to Earth, the data canbe on the Internet and ready for analysis within 15 minutes.
Enthusiasts from all over the world look at each individual imagefor a tiny moving speck that could be a comet. When someone believesthey have found one, they submit their results to Karl Battams at theNaval Research Laboratory, Washington DC, who checks all of SOHO’sfindings before submitting them to the Minor Planet Center, where thecomet is catalogued and its orbit calculated.
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| Close-up on SOHO's 1500th comet
| Thewealth of comet information has value beyond mere classification. “Thisis allowing us to see how comets die,” says Battams. When a cometconstantly circles the Sun, it loses a little more ice each time, untilit eventually falls to pieces, leaving a long trail of fragments.Thanks to SOHO, astronomers now have a plethora of images showing thisprocess. “It’s a unique data set and could not have been achieved inany other way,” says Battams.
All this is on top of the extraordinary revelations that SOHO hasprovided over the 13 years it has been in space, observing the Sun andthe near-Sun environment. “Catching the enormous total of comets hasbeen an unplanned bonus,” says Bernhard Fleck, ESA SOHO ProjectScientist.
Notes for Editors:
Anyone can help to search for SOHO’s comets by visiting the Sungrazing comets page.
The Minor Planet Center operates under the auspices of theInternational Astronomical Union, and is located in Cambridge,Massachusetts.
For more information:
Karl Battams, Naval Research Laboratory, USA
Email: Karl.Battams @ nrl.navy.mil
Bernhard Fleck, ESA SOHO Project Scientist
Email: Bfleck @ esa.nascom.nasa.gov |