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Description
Observations of the Earthshine o the Moon allow for the unique opportunity to measure the large-scale Earth atmosphere. Another opportunity is realized during a total lunar eclipse which, if seen from the Moon, is like a transit of the Earth in front of the Sun. We thus aim at transmission spectroscopy of an Earth transit by tracing the solar spectrum during the total lunar eclipse of January 21, 2019. Time series spectra of the Tycho crater were taken with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in its polarimetric mode in Stokes IQUV at a spectral resolution of 130000 (0.06{AA}). In particular, the spectra cover the red parts of the optical spectrum between 7419-9067{AA}. The spectrograph's exposure meter was used to obtain a light curve of the lunar eclipse. The brightness of the Moon dimmed by 10.75m during umbral eclipse. We found both branches of the O_2_ A-band almost completely saturated as well as a strong increase of H_2_O absorption during totality. A pseudo O_2_ emission feature remained at a wavelength of 7618{AA}, but it is actually only a residual from different P-branch and R-branch absorptions. It nevertheless traces the eclipse. The deep penumbral spectra show significant excess absorption from the NaI 5890{AA} doublet, the CaII infrared triplet around 8600{AA}, and the KI line at 7699{AA} in addition to several hyper-fine-structure lines of MnI and even from BaII. The detections of the latter two elements are likely due to an untypical solar center-to-limb eect rather than Earth's atmosphere. The absorption in CaII and KI remained visible throughout umbral eclipse. Our radial velocities trace a wavelength dependent Rossiter-McLaughlin eect of the Earth eclipsing the Sun as seen from the Tycho crater and thereby confirm earlier observations. A small continuum polarization of the O_2_ A-band of 0.12% during umbral eclipse was detected at 6.3. No line polarization of the O_2_ A-band, or any other spectral-line feature, is detected outside nor inside eclipse. It places an upper limit of 0.2% on the degree of line polarization during transmission through Earth's atmosphere and magnetosphere.
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