charles 2009-3-27 11:00
橫跨南北半球的彗尾
A Tail of Two Hemispheres
[img]http://i5.tinypic.com/2rw5hs1.jpg[/img]
影像版權與提供: S. Deiries (ESO), M. Fulle (INAF)
[color=navy]Explanation: [/color]
[color=dimgray]By January 19/20 Comet McNaught's magnificent dust tail stretched for about 150 million kilometers (~1 AU), requiring images from both southern and northern hemispheres of planet Earth to take it all in. Two such views - from Cerro Paranal in Chile (left) and the Carnic Alps in Italy - are combined in this unique graphic that also outlines a perspective view of the comet's orbit (dotted line) and relative position of the Sun. Driven by solar radiation pressure the dust tail initially points away from the Sun, but also trails outside the comet's orbit. Astronomers try to account for the complex structure along the tail, including the pronounced striations, by considering forces acting on the dust (e.g. gravity, solar wind and radiation) as well as the release time and size of the dust grains. In the diagram, the modeled location of dust grains released at approximately the same time relative to perihelion passage, synchrones, are shown as dashed lines. The location of grains of similar size, syndynes, are shown as solid lines. [/color]
[color=navy]說明:[/color]
[color=dimgray]在今年的1月19/20日之時，麥克諾彗星壯麗的彗尾延伸了大約一億五千萬公里，相當於一個天文單位 (1 AU)的長度，需要組合分別在南半球和北半球所拍攝的影像才得見全貌。上面這張獨特的圖像就是使用在智利Cerro Paranal (左)和義大利Carnic Alps所拍攝的二幅影像組合出來的，影像也包含以透視法呈現的彗星軌道 (點線)，以及太陽的相對位置。在太陽輻射壓的推送下，彗星的塵尾外指，同時也飄落在彗星軌道的外側。天文學家試著要了解彗尾上的複雜構造，尤其是明顯的分層結構；他們考慮了作用在彗尾塵埃粒子上的力 (例如：重力、太陽風和輻射)，以及彗尾微塵的釋放時間和顆粒大小之分佈。在這張圖像裡，相對於近日點，同一時間點釋出的塵埃微粒之模擬位置，是以虛線 (等時線 - synchrones)來標示，而類似顆粒微塵的分佈，則以實線 (等顆粒線 - syndynes)來表示。 [/color]
[size=2]資料來源: Scientific American
Department of Physics, NCKU[/size][color=white][size=1]
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