地球外面包围着一层大气圈。大气圈上下各层的空气具有不同的密度,愈接近地表、密度愈大;愈向高空、空气愈稀薄。高层大气中光学现象十分丰富,如虹、晕、霞、华等。各种不同的光学现象能显示高层大气的物理性质,预示未来天气的变化。一、虹炎热的夏天雨过天晴,常常会在背着太阳那一边的天空出现彩色的圆弧,这就是虹。雨过天晴的空气,悬浮着很多微小的水滴。太阳光沿着一定的角度射入小水滴,入 The earth is surrounded by a layer of atmosphere. The air above and below the atmosphere has different densities. The closer to the surface, the greater the density; the higher the air, the thinner the air. The optical phenomena in the upper atmosphere are very rich, such as rainbow, halo, Xia, Hua and so on. A variety of different optical phenomena can show the physical properties of the upper atmosphere, predicting future changes in the weather. First, rainbow hot weather is fine in summer. It is often a colored arc in the sky on the side of the sun. This is a rainbow. The fine, cloudy air floats with tiny drops of water. Sunlight shoots small droplets of water along a certain angle.