葡京官网

Comet crash spied by the Sun King's court

作者:和早籁    发布时间:2019-02-27 10:10:06    

By Jeff Hecht IN DECEMBER, the surface of Jupiter gave a spectacular display of celestial fireworks that rivalled the impact of Comet Shoemaker-Levy 9 in 1994. You may have missed the great event. The year was 1690. After Shoemaker-Levy broke up and its fragments slammed into Jupiter, astronomers started combing the historical records to discover the frequency of such impacts. Estimates ranged widely. Gene Shoemaker of the US Geological Survey in Flagstaff, Arizona, thought that Jupiter impacts might occur once every thousand years. Brian Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, plumped for once every twenty years. The 300-year-old observations were discovered by Isshi Tabe, a Japanese amateur astronomer, in the Paris Observatory archives. Drawings and a description of the impact were made by Giovanni Cassini, the astronomer to Louis XIV—the Sun King. Several spots that might have been caused by comet impacts have been seen on Jupiter. However, none lasted long enough to provide convincing evidence of an impact. Cassini’s observations were different because they show changes in the spots over 18 days, says Junichi Watanabe of the National Astronomical Observatory of Japan in Mitaka. Cassini noted the sudden appearance of a round, dark spot on Jupiter’s surface on 5 December 1690. From the drawing, Watanabe estimates its diameter was comparable to the spots caused by the medium-sized fragments of Shoemaker-Levy 9. The spot then began to lengthen, spreading out along a line of latitude, just like the scars of the 1994 comet, which remained visible for between 9 and 35 days. Watanabe says that the changes in the shape are “the strongest evidence” that Cassini had observed an impact. Cassini spent most of his life observing Jupiter and Saturn. Modern astronomers consider him among the most reliable historical observers. The Cassini gap in Saturn’s rings is named after him, and a space probe due to begin its journey to Saturn later this year also bears his name. “His telescope was a very excellent one, or his eyes were like an eagle’s,” says Tabe. Tabe analysed the drawings with Watanabe and fellow amateur Michiwo Jimbo, after reading a paper by Cassini. Their findings will appear in the journal Publications of the Astronomical Society of Japan. Professional astronomers remain divided over the value of historical records. “I’m sceptical that anything firm could be deduced,

 

Copyright © 网站地图