£=89.5° the vapor effluent from photodissociation is 3 X 106 Na atoms cm-2s-1. These figures may be slightly reduced due to lower yield because the sodium is more tightly bound in the silicate. In any case, the sodium emission ought to be higher at the poles than at the sunrise equatorial terminator by a factor of 10—102, if lunar cometary recondensate exists. If we assume a mean lifetime of lunar sodium vapor of 2 X 106 sec (about the length of a lunar day) before they are ejected from the atmosphere, considering limb foreshortening we expect a column density of ~1016—1017 Na atoms cm-2 compared to 1014—1015 for the equator from production from lunar regolith (if we use Morgan’s value of a shorter Na lifetime, 1012). Experimental Design And so we now design an inexpensive experiment to detect this difference, if it exists. When sodium vapor was discovered on Mercury [33, 34] a search was made for it on the moon, a morphologically similar body [35] but this had negative results at the expected levels. Subsequently it was detected at a much lower level [36] of 3 X 108 Na atoms cm-2 by Potter & Morgan. The discrepancy between the predicted and observed amounts may be due to a lower yield factor due to tighter bonding of Na in silicates or resorption of vapor in the ‘fairycastle’ structure of the regolith. Three experiments were performed to detect higher sodium vapor at the lunar poles: 1. Low sensitivity scan using Fabry-Perot interference filters; stacked around the D lines; 2. photographic spectrograms of the D lines; 3. reticon spectra using a large cassegrain. This paper described the first experiment, but also discusses preliminary results from the remaining two. Second-order Fabry-Perot interference filters centered on D lines were stacked reducing the bandwidth. A Hoya L-40 was added to eliminate the third-order peak, the telescope optics removing the other leaks. An iris and a photomultiplier tube completed the system (Fig. 2). Comparison readings were taken near full moon of the lunar polar regin and of a region of similar albedo near the lunar limb, so that phase and aspect angles were as close as possible. Albedo similarity was established by prior measurement with a Hoya GV-55 green filter. The sodium line intensity readings included the D line wings and some of the continuous spectrum beyond, so that this experiment would require a 3.3 X1016 Na atoms cm-2 column density difference between poles and equator to produce a 9% average difference in readings. For the telescope, a long focus refractor was preferred since individual areas can be sampled by the iris at the focal plane easier. Objective aperture was not critical since there are plenty of photons at the full moon. Nonetheless, because of the bandpass of the filters, the experiment could only detect sodium emission if it were on the higher end of the estimate. Results Table I gives the results of the experiments performed with the Warner & Swasey refractor of Case-Western Reserve University, 1 July 1988. For the 23 pairs of readings, within the significant figures used, we obtained an identical polar and
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