Transient Lunar Phenomena: Regularity and Reality

Transient lunar phenomena (TLPs) have been reported for centuries, but their nature is largely unsettled, and even their existence as a coherent phenomenon is still controversial. Nonetheless, a review of TLP data shows regularities in the observations; a key question is whether this structure is imposed by human observer effects, terrestrial atmospheric effects or processes tied to the lunar surface. I interrogate an extensive catalog of TLPs to determine if human factors play a determining role in setting the distribution of TLP reports. We divide the sample according to variables which should produce varying results if the determining factors involve humans e.g., historical epoch or geographical location of the observer, and not reflecting phenomena tied to the lunar surface. Specifically, we bin the reports into selenographic areas (300 km on a side), then construct a robust average count for such “pixels” in a way discarding discrepant counts. Regardless of how we split the sample, the results are very similar: roughly 50% of the report count originate from the crater Aristarchus and vicinity, ∼16% from Plato, ∼6% from recent, major impacts (Copernicus, Kepler and Tycho beyond Aristarchus), plus a few at Grimaldi. Mare Crisium produces a robust signal for three of five averages of up to 7% of the reports (however, Crisium subtends more than one pixel). The consistency in TLP report counts for specific features on this list indicate that ∼80% of the reports are consistent with being real (perhaps with the exception of Crisium). Some commonly reported sites disappear from the robust averages, including Alphonsus, Ross D and Gassendi. TLP reports supporting these sites originate almost entirely after year 1955, when TLPs became more popular targets of observation and many more (and inexperienced) observers searched for TLPs. We review non-lunar hypotheses discussed to explain TLP, and find conflicts with the data involving nearly all of them. Furthermore, in a companion paper, we compare the spatial distribution of robust TLP sites of transient outgassing (seen by instruments on Apollo and Lunar Prospector). To a high confidence against the random hypothesis, robust TLP sites and those of lunar outgassing correlate strongly, further arguing for the reality of TLPs.