据专家介绍，日晕是一种罕见的天文现象，它形成的原因是在5000米的高空中出现了由冰晶构成的卷层云，卷层云中的冰晶经过太阳照射后会发生折射和反射等物理变化，阳光便分解成了红、黄、绿、紫等多种颜色，这样太阳周围就出现一个巨大的彩色光环，色带排列内红外紫。
“日晕”有全晕圈和缺口晕，它的出现往往预示天气要有一定的变化。除了日晕，月光也能形成月晕。
The ring you describe is what atmospheric scientists call a "halo" or "glory." It probably looked something like this:
Halos are caused by the light of the sun or moon passing through a very thin layer of cirruform (ice-crystal) clouds in the upper atmosphere. The ice crystals refract the light of the moon, similar to the way water droplets in the lower atmosphere can refract sunlight to produce a rainbow. Just like a rainbow, strong halos can have bands of color in them, due to slightly different refractive properties of the ice crystals for different colors. Essentially, halos ARE rainbows caused by primary refraction in ice crystals.
Some interesting facts about halos: Halos always occur exactly 22 degrees away from the sun or moon. Occasionally, intense halos can be double halos, just as intense rainbows can be doubled. Intense halos can also produce "moondogs" or "sundogs," very bright regions on the halo evenly spaced at 90 degree intervals around the halo.
Have a look at this link. There are some very nice pictures of halos and moondogs there, as well as some informative diagrams showing how the light is bent by the ice crystals.
More Information on this phenomena please visit :
http://curious.astro.cornell.edu/question.php?number=79
http://scitech.people.com.cn/GB/6086414.html
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