2017年11月30日:M33: 三角座大星系-（M33: Triangulum Galaxy）--原图下载
Image Credit &Copyright:Peter Nagy
说明: 这个壮丽的正向螺旋星系，是位在三角座这个北天小星座内的M33。常称为是风车星系或三角座大星系的M33，直径超过50,000光年，是本星系群里大小仅次于仙女座大星系和我们银河系的第三大星系。大约离银河系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。至于从地球拍摄的这幅高清组合影像，则巧妙地呈现M33鬆散螺旋臂上的蓝色星云和粉红色恒星形成区。而位在星系核心7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，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，可用来测定宇宙的距离尺标。
原文：
Image Credit &Copyright:Peter Nagy
Explanation: The small, northern constellationTriangulumharbors this magnificent face-on spiral galaxy, M33.Its popular names include the Pinwheel Galaxy or justthe Triangulum Galaxy.M33 is over 50,000 light-years in diameter, third largest in theLocalGroup of galaxies after the Andromeda Galaxy (M31), and ourown Milky Way.About 3 million light-years from the Milky Way,M33 is itself thought to be a satellite of theAndromeda Galaxy andastronomersin these two galaxies would likely have spectacular views ofeach other's grand spiral star systems.As for the view from planet Earth,thissharp composite image nicely shows off M33's blue star clustersand pinkish star forming regions alongthe galaxy's loosely wound spiral arms.In fact, thecavernous NGC 604 is thebrightest star forming region, seen here at about the 7 o'clock positionfrom the galaxy center.Like M31, M33's population of well-measured variable starshave helped make this nearby spiral a cosmic yardstick forestablishingthe distance scale of the Universe.
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