The pandemic-induced lock-down has resulted in better air quality and visibility, with reported sightings of Himalayan peaks from hundreds of kilometers away. During the 18th and 19th centuries, good visibility was commonplace and there exist many such accounts by reputable Orientalists such as Henry Colebrooke and Sir William Jones. These sightings invite two questions. Is a line of sight to the peak even possible from the location? Is the location close enough and the intensity of visible light sufficient for the peak to be seen? The present work explores both these aspects in the context of the Himalayan peaks. The effects of the curvature of the Earth and refraction on the perceived heights of several mountains in the eastern Himalayas are considered. The effects of Rayleigh scattering by the atmosphere on the visibility of these peaks are also considered as an extension of the work done by Weisskopf. Some historically significant details and a possible inaccuracy in an account by Sir William Jones are discussed. The approach is pedagogical and is not specialized to the eastern Himalayas, so it can be applied readily to other locations, for example, the Andes in South America.

中文翻译：

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从平原上看喜马拉雅山

由大流行引起的封锁已导致更好的空气质量和能见度，据报导看到数百公里之外的喜马拉雅山峰。在18和19世纪，能见度很高是司空见惯的，并且有许多这样的著名的东方主义者的著作，例如亨利·科尔布鲁克（Henry Colebrooke）和威廉·琼斯爵士（Sir William Jones）。这些目击者提出了两个问题。从该位置到山顶的视线是否还可能？位置是否足够靠近并且可见光的强度足以看到峰？本工作在喜马拉雅山峰的背景下探讨了这两个方面。考虑了地球曲率和折射对喜马拉雅山脉东部几座山的感知高度的影响。大气的瑞利散射对这些峰的能见度的影响也被认为是魏斯科普夫所做工作的延伸。讨论了一些历史上重要的细节，以及威廉·琼斯爵士的帐户中可能存在的错误。这种方法是教学方法，不是专门针对喜马拉雅山脉东部地区，因此可以很容易地应用于其他地区，例如南美的安第斯山脉。