M57：哈勃拍摄的环状星云
(原标题: M57: The Ring Nebula from Hubble)
2021-08-17
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除了土星环，环状星云（M57）可能是最著名的天体环。它的经典外观被认为是由于我们自己的观点。最近对这个正在膨胀的星云的三维结构的绘制，部分是基于这张清晰的哈勃图像，表明这个星云是一个相对致密的，像甜甜圈一样的环，包裹在一个（美式）足球形状的发光气体云的中间。从地球上看到的是足球的长轴，正对着圆环。当然，在这个被充分研究的行星状星云的例子中，发光的物质并不是来自行星。相反，气体裹尸布代表了这颗垂死的、曾经像太阳一样的恒星所排出的外层，现在在星云中心可以看到一个微小的光点。来自炽热中央恒星的强烈紫外线使气体中的原子电离。环状星云直径约1光年，距离我们2500光年。共享天空：NASA APOD开放API
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cept for the rings of Saturn, the Ring Nebula (M57) is probably the most famous celestial circle. Its classic appearance is understood to be due to our own perspective, though. The recent mapping of the expanding nebula's 3-D structure, based in part on this clear Hubble image,indicates that the nebula is a relatively dense, donut-like ring wrapped around the middle of a (American) football-shaped cloud of glowing gas. The view from planet Earth looks down the long axis of the football, face-on to the ring. Of course, in this well-studied example of a planetary nebula, the glowing material does not come from planets. Instead, the gaseous shroud represents outer layers expelled from the dying, once sun-like star, now a tiny pinprick of light seen at the nebula's center. Intense ultraviolet light from the hot central star ionizes atoms in the gas. The Ring Nebula is about one light-year across and 2,500 light-years away. Share the Sky: NASA Open API for APOD