Daytime Sky Brightness at Dome C, Antarctica: Results from All ESCAPE Campaigns

Abstract The study of the solar corona is a prominent focus in the field of solar physics. However, conducting ground-based observations of the corona is a challenging task due to the interference caused by the diffused sky brightness, which obscures the faint coronal signal. As a result, such observations are primarily carried out during total solar eclipses. The requirement of a sky-brightness level as low as $10^{-6}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> </mml:msup> </mml:math> times the solar disk brightness ( $B_{\odot }$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>B</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> </mml:math> ) is met by few places on Earth, and currently there are only two sites hosting solar observatories that satisfy this criterion, Mauna Loa and Haleakala, both located in Hawaii. Nevertheless, another candidate coronagraphic site was discovered in the Concordia Station at Dome C plateau, Antarctica ( $\simeq 3300$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>≃</mml:mo> <mml:mn>3300</mml:mn> </mml:math> m a.s.l.). In this article, we show the last results of the Extreme Solar Coronagraphy Antarctic Program Experiment (ESCAPE) during the 38th summer campaign of the Italian Piano Nazionale di Ricerche in Antartide (PNRA). Here, we report a model for estimating the air column, which allows for the first time to account for variations in the Sun’s altitude above the horizon during different observation periods, and we use it to compare the obtained results with previous campaigns. Our results confirm that Dome C is an ideal coronagraphic site with the required sky-brightness level, reaching $1.0-0.7\times 10^{-6}B_{\odot }$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mn>1.0</mml:mn> <mml:mo>−</mml:mo> <mml:mn>0.7</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> </mml:msup> <mml:msub> <mml:mi>B</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> </mml:math> in optimal conditions.