charles 2009-3-23 10:50
天龍座三劍客
Three Galaxies in Draco
[img]http://i3.tinypic.com/43w0aip.jpg[/img]
影像提供 : Stefan Heutz, Wolfgang Ries, Cord Scholz
[color=navy]Explanation:[/color]
This intriguing trio of galaxies is sometimes called the NGC 5985/Draco Group and so (quite reasonably) is located in the northern constellation Draco. From left to right are face-on spiral NGC 5985, elliptical galaxy NGC 5982, and edge-on spiral NGC 5981 -- all within this single telescopic field of view spanning a little more than half the width of the full moon. While this grouping is far too small to be a galaxy cluster and has not been cataloged as a compact group, these galaxies all do lie roughly 100 million light-years from planet Earth. On close examination with spectrographs, the bright core of the striking face-on spiral NGC 5985 shows prominent emission in specific wavelengths of light, prompting astronomers to classify it as a Seyfert, a type of active galaxy. Not as well known as other tight groupings of galaxies, the contrast in visual appearance makes this triplet an attractive subject for astrophotographers. This impressively deep exposure of region also reveals faint and even more distant background galaxies.
[color=navy]說明:[/color]
上面這三個很有意思的星系，位在北天的天龍座 (Draco)內，常被稱為是NGC 5985天龍座群 (NGC 5985/Draco Group)。這小群離我們大約一億光年的星系，從左至右分別是正面對著我們的NGC 5985、 橢圓星系NGC 5982、和側對著我們的NGC 5981，通常在單一個望遠鏡視野內就能同時看見它們，因為它們的寬度只比滿月的一半要多一點而已。 這群星系太小了，所以不能算作是星系團，而且它們也沒有被歸類成一個緻密群。 用光譜儀仔細研究過正面對著我們的螺旋星系NGC 5985後，天文學家發現它的核心在某些波段有很強的輻射，也因此它被歸類成西佛星系，是一種活躍星系。 天龍座三劍客雖然並不像其他緊密星系群那麼出名，不過它們在視覺上的強烈對比，讓它們成為天文攝影愛好者常常拍攝的對象之一。 在這個天區的精彩長時曝光影像裡，還可以看見更遙遠的昏暗背景星系。
[size=2]資料來源: Scientific American
Department of Physics, NCKU[/size]