IC 2118: 女巫头星云

2023年10月4日

IC 2118: The Witch Head Nebula
Image Credit & Copyright: Abdullah Alharbi

Explanation: Does this nebula look like the head of a witch? The nebula is known popularly as the Witch Head Nebula because, it is said, the nebula’s shape resembles a Halloween-style caricature of a witch’s head. Exactly how, though, can be a topic of imaginative speculation. What is clear is that IC 2118 is about 50 light-years across and made of gas and dust that points to — because it has been partly eroded by — the nearby star Rigel. One of the brighter stars in the constellation Orion, Rigel lies below the bottom of the featured image. The blue color of the Witch Head Nebula and is caused not only by Rigel’s intense blue starlight but because the dust grains scatter blue light more efficiently than red. The same physical process causes Earth’s daytime sky to appear blue, although the scatterers in planet Earth’s atmosphere are molecules of nitrogen and oxygen.

Tomorrow’s picture: open space

IC 2118: 女巫头星云
影像提供与版权: Abdullah Alharbi

说明: 这个星云看起来像女巫的头吗？这个星云之所以有”女巫头星云”的称号，则是因为它的外观形似万圣节风格漫画的女巫之头部。不过，它究竟是如何形成的，至真仍是一个富有想像力的题材。很可确定的是，IC 2118约有50光年宽，由气体和尘埃所组成，并且面向附近的参宿七，因为它已被这颗恒星侵蚀掉了一部分。参宿七是猎户座的亮星之一，位于这张主题影像的底缘下方。女巫头星云的泛蓝色泽，除了因为参宿七强烈的泛蓝星光之外，也因为它的尘埃微粒散射蓝光的效率高于红光。同样的物理过程也造就了地球白昼的蓝天，只不过地球大气里的散射体是氮和氧分子。