M33：三角星系

2019 December 31

M33: The Triangulum Galaxy
Image Credit & Copyright: Rui Liao

Explanation: The small, northern constellation Triangulum harbors this magnificent face-on spiral galaxy, M33. Its popular names include the Pinwheel Galaxy or just the Triangulum Galaxy. M33 is over 50,000 light-years in diameter, third largest in the Local Group of galaxies after the Andromeda Galaxy (M31), and our own Milky Way. About 3 million light-years from the Milky Way, M33 is itself thought to be a satellite of the Andromeda Galaxy and astronomers in these two galaxies would likely have spectacular views of each other’s grand spiral star systems. As for the view from planet Earth, this sharp image shows off M33’s blue star clusters and pinkish star forming regions along the galaxy’s loosely wound spiral arms. In fact, the cavernous NGC 604 is the brightest star forming region, seen here at about the 7 o’clock position from the galaxy center. Like M31, M33’s population of well-measured variable stars have helped make this nearby spiral a cosmic yardstick for establishing the distance scale of the Universe.

M33：三角星系
影像来源与版权: Rui Liao

说明：壮丽的正向旋涡星系M33位于北天的小星座-三角座内。它被昵称为风车星系或三角星系。直径超过5万光年的M33是本星系群中、仅次于仙女星系（M31）和银河系的第三大星系。距离银河系300万光年的M33被认为是仙女星系的伴星系之一，位于这两个星系的天文学家都会看到对方壮观的旋涡状恒星系统。至于这幅从地球上拍摄的清晰影像则呈现了沿着松散旋臂分布的M33的蓝色恒星团和粉红色恒星形成区。实际上，洞穴状的NGC 604是最明亮的恒星形成区，它位于星系中心的七点钟方向。与M31类似，M33内经过精准测量的变星使得这个邻近的旋涡星系可以当做一把测量宇宙距离的尺子。