The Spectrum of Earthshine: A Pale Blue Dot Observed from the Ground

Abstract

We report the visible reflection spectrum of the integrated Earth, illuminated as it would be seen as an spatially-unresolved extrasolar planet. The spectrum was derived from observation of lunar earthshine in the range 4800 to 9200 Angstrom at a spectral resolution of about 600. We observe absorption features of ozone, molecular oxygen and water. We see enhanced reflectivity at short wavelengths from Rayleigh scattering, and apparently negligible contributions from aerosol and ocean water scattering. We also see enhanced reflectivity at long wavelengths starting at about 7300 Angstrom, corresponding to the well-known red reflectivity edge of vegetation due to its chlorophyll content; however this signal is not conclusive, due to the breakdown of our simple model at wavelengths beyond 7900 Angstrom.