Optical polarimetry of the May 2022 lunar eclipse

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 percent in B, 1.2 +/- 0.3 percent in V, 0.5 +/- 0.2 percent in R, and 0.2 +/- 0.2 percent 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 percent) 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.

Automated summary

We conducted polarization observations during the totality of the lunar eclipse on May 16, 2022. The results showed polarization degrees of 2.1% ± 0.4% in B, 1.2% ± 0.3% in V, 0.5% ± 0.2% in R, and 0.2% ± 0.2% in I. These findings provide further evidence that the change in polarization is event-dependent and support the interpretation that the polarization originates from scattering in the Earth's atmosphere.