M33：三角大星系
M33: The Triangulum Galaxy
Image Credit & Copyright: Bernard Miller
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 4 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.
Tomorrow’s picture: 67P
M33：三角大星系
影像提供版权: Bernard Miller
说明: 这个壮丽的正向螺旋星系（M33），位在北天的小星座三角座之内。经常称为风车星系或三角大星系的M33，直径超过50,000光年，在本星系群里，是大小仅次于仙女座大星系（M31）和我们银河系的第三大星系。离银河系大约3百万光年远的M33，咸认是仙女座大星系的伴星系之一；也因此，位在这二个星系的天文学家，应该都能看见对方宏伟的旋涡状恒星系统。至于在地球拍摄的这幅高清组合影像，则精采的呈现了M33松散螺旋臂上的泛蓝星云和粉红恒星形成区。位在星系核心4点钟方向的洞穴状NGC 604，就是其中最明亮的恒星形成区。类似星系M31的案例，M33内经过仔细量测的变星，让这个邻近的螺旋星系就像一把量天尺，可用来规范宇宙的尺度。
明日的图片: 67P
