Twilights Spectral and Spatial Structure in the Visible

自然光可能被大气成分折射、吸收或散射。对这些影响的研究构成了大气光学，这是理论气象学中最古老的分支。它的早期发展与天文学有关，因为大气对遥远的观看施加了限制。多年来，许多杰出的人物为这一主题做出了贡献。达芬奇在追求绘画现实主义的过程中，研究了彩虹现象和视觉对比度随距离减小的问题。艾萨克·牛顿根据他对彩虹和后来的光晕的折射实验给出了解释。1871年，约翰·斯特鲁特(后来的瑞利勋爵)发表了著名的散射理论，用来解释晴朗天空中光线的颜色和偏振。这个项目延续了长期以来的传统，试图通过关注天空中最复杂的现象之一--黄昏来解释为什么天空看起来是这样的。数码摄影和光谱辐射测量法被用来测量基本上整个黄昏天空的亮度、颜色和偏振。这些观测结果与现有的基于大气颗粒和气体散射和吸收的理论模型进行了比较，以此来测试和改进模型。这项研究的目的是开发准确的暮光模型，其中包括分子和背景气溶胶的散射、臭氧和其他气体的吸收以及火山颗粒或有时可能存在的其他大型气溶胶的散射和吸收的影响。

Natural light may be refracted, absorbed, or scattered by atmospheric constituents. The study of these effects constitutes atmospheric optics, the oldest branch of theoretical meteorology. Its early development was related to astronomy because of the limitations imposed by the atmosphere on distant seeing. Through the years, many outstanding figures contributed to the subject. In his quest for realism in painting, Leonardo da Vinci studied the phenomena of the rainbow and the reduction of visual contrast with range. Isaac Newton gave explanations based on his experiments on refraction for the rainbow, and later the halo. The celebrated scattering theory published in 1871 by John Strutt (later Lord Rayleigh) was developed to explain the color and polarization of light from the clear sky. This project continues the long tradition of attempting to explain why the sky looks the way it does by focusing on one of its most complex phenomena, twilight. Digital photography and spectroradiometry are used to measure the brightness, color, and polarization of essentially the entire twilight sky. The observations are compared with existing theoretical models based on scattering and absorption by atmospheric particles and gases as a way of testing the models and improving them. The objective of the study is to develop accurate models for twilight that include the effects of scattering by molecules and background aerosols, absorption by ozone and other gases, and scattering and absorption by volcanic particles or other large aerosols that may sometimes be present.