2025年6月27日
Messier 109
Image Credit & Copyright: Robert Eder
Explanation: Big beautiful barred spiral galaxy Messier 109 is the 109th entry in Charles Messier’s famous catalog of bright Nebulae and Star Clusters. You can find it just below the Big Dipper’s bowl in the northern constellation Ursa Major. In fact, bright dipper star Phecda, Gamma Ursa Majoris, produces the glare at the upper right corner of this telescopic frame. M109’s prominent central bar gives the galaxy the appearance of the Greek letter “theta”, θ, a common mathematical symbol representing an angle. M109 spans a very small angle in planet Earth’s sky though, about 7 arcminutes or 0.12 degrees. But that small angle corresponds to an enormous 120,000 light-year diameter at the galaxy’s estimated 60 million light-year distance. The brightest member of the now recognized Ursa Major galaxy cluster, M109 (aka NGC 3992) is joined by spiky foreground stars. Three small, fuzzy bluish galaxies also on the scene, identified (top to bottom) as UGC 6969, UGC 6940 and UGC 6923, are possibly satellite galaxies of the larger barred spiral galaxy Messier 109.
Tomorrow’s picture: light-weekend
M109
影像提供与版权: Robert Eder
说明: 庞大美丽的棒旋星系M109，是梅西耶著名的亮星云与星团星表的第109号天体。在北天大熊座北斗七星的斗杓下方，可以见到它的芳踪。而在这片望远镜视野里，右上角带芒的亮星，即是北斗七星斗杓上的天玑（Phecda）。M109鲜明的核心棒，让它形似数学上常用来表示角度的符号、希腊字母θ（theta）。在地球的天空中，M109的视张角非常之小，大约只有7角分或说是0.12度。不过，以此星系约6千万光年的距离来换算，这个小张角对应的却是12万光年的庞然跨幅。此外，周围有带芒前景恒星为伴的M109（亦名为NGC 3992），也是大熊星系群最明亮的成员。视野里三个有点模糊的泛蓝星系，由上到下，分别是UGC 6969、UGC 6940及UGC 6923，而它们则可能是庞大棒旋星系M109的伴星系。
明日的图片: light-weekend