A Sun Halo Over Kaohsiung, Taiwan

These pictures were taken in Kaohsiung at noon on June 28, 2007.

Is it a circular rainbow? No. It's a sun halo. When sunlight passes through an ice crystal, it is refracted. It bends 22 degrees toward the observer from its original direction. The formation of a halo is different from that of a rainbow. A rainbow develops when sunlight enters a water droplet and is refracted and reflected. The sunlight bends about 140 degrees for primary rainbow and about 130 degrees for secondary rainbow from its original direction.

There are some pictures with brief explanations about sun halo from NASA:
1. APOD: 2006 April 11 - A Sun Halo over Utah
2. APOD: 2006 June 13 - Driving Toward a Sun Halo
3. APOD: 2002 January 14 - Sun Halo at Winter Solstice

Here is a wonderful website, Atmospheric Optics.

日暈現高雄

今天(2007/6/28)中午高雄出現日暈。日暈不是彩虹。當光線穿過高空的冰晶時，因折射而偏離原來方向22度，就會在光源周圍形成22度暈，光源如果是太陽就叫日暈，如果是月亮就叫月暈。
彩虹則是太陽光經高空中的小水滴折射及反射所形成，對虹而言光線偏離原方向約140度，而霓(即第二道彩虹，在虹的外圍)則偏離約130度。

下面是有關日暈的一些網站，NASA提供，成大物理系翻譯：
APOD: 2006 April 11 - A Sun Halo over Utah
APOD: 2006 June 13 - Driving Toward a Sun Halo
APOD: 2002 January 14 - Sun Halo at Winter Solstice

這個網站很棒，值得用力推薦，可惜沒有翻譯！Atmospheric Optics