Radial velocity observations of the extended lunar sodium tail

Abstract

We report the first velocity resolved sodium 5889.950 Å line profile observations of the lunar sodium tail observed in the anti‐lunar direction near new Moon. These observations were made on 29 March 2006, 27 April 2006 and 28 April 2006 from Pine Bluff (WI) observatory with a double etalon Fabry‐Perot spectrometer at a resolving power of ∼80,000. The observations were made within 2–14 hours from new Moon, pointing near the anti‐lunar point. The average observed radial velocity of the lunar sodium tail in the vicinity of the anti‐lunar point for the three nights reported was 12.4 km s−1 (from geocentric zero). The average Doppler width of a single Gaussian fit to the emission line was 7.6 km s−1. In some cases the line profile appears asymmetric, with excess lunar sodium emission at higher velocity (∼18 km s−1 from geocentric zero) that is not accounted for by our single Gaussian fit to the emission.