Using a New Sky Brightness Monitor to Observe the Annular Solar Eclipse on 15 January 2010

TL;DR

A new sky brightness monitor was successfully tested during the 2010 annular solar eclipse, demonstrating its high sensitivity and potential for site surveys for the Chinese Giant Solar Telescope by accurately measuring sky brightness and atmospheric scattering.

Contribution

This paper introduces a new sky brightness monitor and validates its performance during a solar eclipse, showing its suitability for site surveys for large solar telescopes.

Findings

The monitor accurately tracked sky brightness changes during the eclipse.

Sky brightness measurements aligned with eclipse contacts within half a minute.

Data indicates single-scattering dominates atmospheric scattering under observed conditions.

Abstract

For the future development of Chinese Giant Solar Telescope (CGST) in Western China, a new sky brightness monitor (SBM) has been produced for the site survey for CGST. To critically examine the performance and sensitivity of SBM, we used it in the observation of the annular solar eclipse in Dali City, Yunnan, on 15 January 2010. The observation met good weather condition with almost clear sky during the eclipse. The SBM measurement translates into the solar illuminance changes at a level of 2.4 \times 10-4I s-1 during the eclipse. The time of the minimal sky brightness in the field of view (FOV) is found consistent with the time of maximum eclipse. Two local sky regions in the FOV are chosen to make time series of calibrated skylight profiles. The evolution of the sky brightness thus calibrated also shows good consistency with the eclipse, particularly between the second and the third contacts. The minimal sky brightness in each local sky region took place within half a minute from the corresponding predicted contact time. Such small time delays were mainly caused by occasional cirri. The minimal sky brightness measured during the eclipse is a few millionths of I\odot with standard deviation of 0.11 millionths of I\odot. The observation supports that the singlescattering process (optically thin conditions) is the main contributor to the atmospheric scattering. We have demonstrated that many important aerosol optical parameters can be deduced from our data.We conclude that the new SBM is a sensitive sky photometer that can be used for our CGST and coronagraph site surveys.