The solar corona is the primary driver of the solar storms and space weather. In order to routinely monitor the coronal activities, a dedicated solar telescope is essential, a coronagraph. However, the site conditions suitable for a ground-based coronagraph are rather critical and necessitate stringent site selection criteria. Among the numerous astronomical observatory site parameters, the sky background brightness of the day is recognized as a key parameter in evaluating the quality of a solar observatory for coronal observation before considering to install a coronagraph. To achieve optimal sky brightness observing condition, coronagraphs are usually installed on high mountains where the atmosphere is thin and the background scattered light effects from the sky are significantly reduced. Given the unique characteristics of the Tibetan Plateau, often referred to as the “Third Pole” of the Earth, a scientific assessment is crucial to evaluate its suitability as a potential location for the next-generation Chinese Giant Solar Telescope and large coronagraphs. Here, we report the first results of our measurements of the sky brightness at the Namco Lake location (30°45.0′N, 90°40.0′E, 4730 m above sea level, the highest large lake in the world), using a new Sky Brightness Monitor during the period 2013 August to December. The results show that the average value of the normalized (per airmass) sky brightness is as low as 13.84 μI⊙ for 530 nm. The excellent sky brightness conditions at the Namco Lake location demonstrate its high suitability for routine coronal observations. Therefore, the Namco site deserves attention for solar observations and we should continue to carry out in-depth monitoring and systematic study of multiple parameters in the future.

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