Optical polarimetry of the May 2022 lunar eclipse

Abstract

The sunlight reflected from the Moon during a total lunar eclipse has been transmitted through the Earth's atmosphere on the way to the Moon. The combination of multiple scattering and inhomogeneous atmospheric characteristics during that transmission can potentially polarize that light. A similar (although much smaller) effect should also be observable from the atmosphere of a transiting exoplanet. We present the results of polarization observations during the first 15 min of totality of the lunar eclipse of 2022 May 16. We find degrees of polarization of 2.1 ± 0.4 per cent in B, 1.2 ± 0.3 per cent in V, 0.5 ± 0.2 per cent in R, and 0.2 ± 0.2 per cent in I. Our polarization values lie in the middle of the range of those reported for previous eclipses, providing further evidence that the induced polarization can change from event to event. We found no significant polarization difference (<0.02 per cent) between a region of dark Mare and nearby bright uplands or between the lunar limb and regions closer to the disc centre due to the different angle of incidence. This further strengthens the interpretation of the polarization's origin being due to scattering in the Earth's atmosphere rather than by the lunar regolith. © 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.