OBSERVATIONS OF SODIUM IN THE LUNAR ATMOSPHERE DURING INTERNATIONAL LUNAR ATMOSPHERE WEEK, 1995

We report results of a part of an organized effort of five observing g roups to simultaneously observe sodium in the lunar atmosphere. Intern ational Lunar Atmosphere Week spanned the week of September 15-22, 199 5. Of the seven nights, we experienced four nights with good viewing c onditions. We used the Mt. Lemmon Lunar Coronagraph (MLLC) and DARRK s pectrograph. Both are especially designed for lunar atmospheric measur ements from the surface extending to an altitude of approximately 1 lu nar radius or similar to 1700 km (860 km geopotential height). Emissio n rates for Na were compatible with those previously reported for rela tively large phase angles (96 degrees to 129 degrees) with the average total of D2 and D1 emission rate similar to 6.9 kRayleigh. A thermal component was observed only on the night of September 17, when the sol ar zenith angle at the limb was only 6 degrees. We observed a factor o f similar to 2 greater column abundances over the north pole than over the sunlit equatorial limb on September 18 while on September 19, the equatorial bright limb column abundance was a factor of similar to 5 higher than the north polar. Apparent geopotential scale heights varie d from 279 to 435 km, indicating an extended atmosphere. If the scale heights are represented by a temperature, values are 985 to 1470 K. Th e data set appears to support the idea that the dominant source during this period was meteoritic impact volatilization. (C) 1998 Academic P ress.