On viewing the Himalayas from the plains

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.