天文读图21-22

A Meteoric View of Apollo 13

阿波罗13号流星般掠影

Meteors, also called shooting stars, normally begin as bits of dust from the tails of comets or even small pieces chipped off asteroids. Falling toward Earth, these particles enter the atmosphere at extremely high speeds. Friction with the air heats them up and makes them glow brightly. Their rapid motion across the sky causes them to show up as bright streaks in photographs. In this picture, however, the bright streaks which appear to be meteor trails are believed to be two large pieces of the Apollo 13spacecraft, the service and lunar modules, reentering the atmosphere.

流星群，也称流星雨，通常是慧星慧尾的尘埃或者从小行星上脱落的小块物质引起的。在坠落到地球的过程中，这些颗粒以极高的速度穿越大气层，与空气的摩擦使它们发热，并产生亮光。它们天空中高速移动，使得在照片中看上去像一道明亮的光痕。在本图中，明亮的光痕看似流星，但实际上是阿波罗13号的两个组件—返回大气层的服务舱和登月舱。

A Galaxy Cluster Lens

星系团透镜
Sometimes one of the largest concentrations of mass known can act like a lens. Almost all of the bright objects in this image are galaxies in the cluster known as Abell 2218. The cluster is so massive and so compact that it bends light from galaxies that lie behind it, causing many of them to appear as stretched out arcs. Many dim, elongated arcs are visible on this photograph. This picture was taken with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope.

有时，一个庞大紧密的聚团具有透视镜的效果。本图中，几乎所有的发光物体都是一个被称为“Abell 2218星系团”中的一员。由于该星系团十分庞大而紧密，使得背后星系发出的光线发生扭曲，像是延伸出来的一条条弧线。图片中，可以看见许多微弱细长的弧线。这张图片是由哈勃望远镜“广角行星相机”拍摄的。