Radial Velocity Observations of the Extended Lunar Sodium Tail

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.