Detection of “Diffuse” Coronal He I 1083 During the April 8, 2024 Solar Eclipse: Evidence for Terrestrial Atmospheric Scattering Contribution

Strong He i 1083 nm atomic line signals have previously been measured during total solar eclipses at coronal heights above the lunar limb. These rather unexpected measurements have kindled a discussion about the suggested presence of significant amounts of neutral helium at coronal conditions. We performed spectroscopic observations of the He i 1083 nm wavelength region during the April 8th, 2024 total solar eclipse, using an instrument specifically designed to test the presence of He i 1083 in the solar corona. We were able to detect the He i 1083 line, the forbidden coronal line of Fe xiii at 1074.7 nm, as well as the chromospheric H i 1093.8 nm (Paschen-γ) line in our data. The chromospheric He i 1083 nm and H i 1093.8 nm lines were detected in both the corona and on the lunar disc. We hypothesize that our observations support a terrestrial atmospheric scattering of the solar flash spectrum as the origin of the He i 1083 signal during the April 8th, 2024 eclipse. Our findings challenge the notion of abundant neutral helium in the solar corona suggested by previous eclipse observations.