WHAM Observations of the Extended Lunar Sodium Tail

The moon is known to possess an extended tail of lunar sodium atoms that is presumably formed when high-energy solar wind particles and meteorites liberate sodium atoms from the lunar surface with velocities greater than the lunar escape velocity. These atoms are propelled outward in the anti-solar direction by radiation pressure in a process similar to that of a comet. Our early observations determined that the average radial velocity of the lunar sodium tail in the vicinity of the anti-lunar point (i.e., looking down the lunar tail as it moves beyond the Earth, along the Sun-Moon-Earth line) is 12.5 km/s. We recently used the Wisconsin H-alpha Mapper (WHAM) to map the intensity and velocity distribution of this emission over a 15 by 15 degree region on the sky near the anti-lunar point. In this poster we present spatial maps obtained over four nights centered on new moon in October 2007. These maps indicate that the spatial distribution of the sodium atoms is elongated along the ecliptic with the location of the peak intensity drifting 3 degrees east along the ecliptic per night.