微笑的彩虹

2022年3月11日

When Rainbows Smile
Image Credit & Copyright: Marcella Giulia Pace

Explanation: Want to see a rainbow smile? Look near the zenith (straight up) when the sun is low in the sky and you might. This example of an ice halo known as a circumzenithal arc was captured above a palm tree top from Ragusa, Sicily on February 24. The vividly colorful arcs are often called smiling rainbows because of their upside down curvature and colors. For circumzenithal arcs the zenith is at the center and red is on the outside, compared to rainbows whose arcs bend toward the horizon after a downpour. True rainbows are formed by water droplets refracting the sunlight to produce a spectrum of colors, though. Circumzenithal arcs are the product of refraction and reflection in flat hexagonal ice crystals, like the ice crystals that create sundogs, formed in high thin clouds.

Tomorrow’s picture: Point Reyes Milky Way

微笑的彩虹
影像提供与版权: Marcella Giulia Pace

说明: 想看微笑的彩虹吗？当太阳处在低矮的位置时，如你往头顶看，或许就有机会。上面这例称为环天顶弧的冰晕，是在2月24日出现在西西里岛拉古萨市一颗棕榈树的上方。这种色彩鲜明的虹弧，亦称为微笑彩虹，因为它弯曲的方向和色彩排列和一般的彩虹相反。对环天顶弧而言，天顶在它的中心，而红色在外缘，相较之下，在倾盆大雨后出现的彩虹里，其虹弧弯向地平面。一般的彩虹来自小水滴折射阳光，把光解析成七彩色谱。环天顶弧则是扁平六角冰晶折射与反射阳光的产物，此外，位在高层薄云的这类冰晶，也会产生幻日景观。 （Circumzenithal Arc 环天顶弧）

明日的图片: Point Reyes Milky Way