2025年8月14日
M13: The Great Globular Cluster in Hercules
Image Credit & Copyright: R. Jay Gabany
Explanation: In 1716, English astronomer Edmond Halley noted, “This is but a little Patch, but it shews itself to the naked Eye, when the Sky is serene and the Moon absent.” Of course, M13 is now less modestly recognized as the Great Globular Cluster in Hercules, one of the brightest globular star clusters in the northern sky. Sharp telescopic views like this one reveal the spectacular cluster’s hundreds of thousands of stars. At a distance of 25,000 light-years, the cluster stars crowd into a region 150 light-years in diameter. Approaching the cluster core, upwards of 100 stars could be contained in a cube just 3 light-years on a side. For comparison with our neighborhood of the Milky Way, the closest star to the Sun is over 4 light-years away. Early telescopic observers of the great globular cluster also noted a curious convergence of three dark lanes with a spacing of about 120 degrees, seen here just below the cluster center. Known as the propeller in M13, the shape is likely a chance optical effect of the distribution of stars viewed from our perspective against the dense cluster core.
Tomorrow’s picture: pixels in space
武仙座大球状星团M13
影像提供与版权: R. Jay Gabany
说明: 在1716年，英国天文学家哈雷写下了这个注记：「它只是夜空的小亮斑，不过当夜空清朗无月时，用肉眼就能看见它。」如今我们知道，M13其实是武仙座方向的大球状星团，也是北半球天空中最明亮的球状星团之一。诸如这样的清晰望远镜影像，显示这个庞大的星团拥有数十万颗恒星。以这个星团25,000光年的距离来估算，星团的成员星挤在直径约为150光年的范围内。而在此星团的核心区，边长仅3光年的立方体内可能就有100多颗恒星。相较之下，于我们所在的银河区，离太阳最近的恒星其间距超过4光年。这个大球状星团早期的观测者指出，它的中心下方有三道间隔约120度的会聚暗带。这个称为M13的螺旋桨之结构，可能是从我们所在的置看过去，其恒星分布在致密星团核心前方偶然造成的光学效应。
明日的图片: pixels in space
