Preliminary Analysis of Transient Lunar Phenomena Catalog Data

Introduction: With recent interest in Transient Lunar Phenomena (TLP) and lunar out-gassing theories [1-3], the TLP catalogs of Middlehurst [4] and Cameron [5] are frequently quoted in references. However there are many issues that affect the quality of TLP reports and observer interpretation of the Moon’s surface, which may not be appreciated fully. Therefore as part of collaboration between Aberystwyth University, and amateur astronomers from the British Astronomical Association (BAA) and the Association of Lunar and Planetary Observers (ALPO), many TLP sites are being re-examined under the same illumination (to within ±0.5o), and where possible libration, of the conditions under which the TLP were seen originally. This will establish the normal appearances of the features concerned. However in order to achieve this we have had to compile a new catalogue of TLP reports based upon the earlier catalogs, Cameron’s extended catalog [6], and more recent ALPO and BAA TLP reports. Although the Cameron catalogs include observational weights, recent publications about atmospheric dispersion, turbulence [7] and shadow effects [8] show how these can contribute to mis-interpretation of TLPs, and imply that many of these rankings could be doubtful. We are therefore re-evaluating all the weights, but in the short term have produced some preliminary frequency plots. Method: In order to populate the new combined catalog, a sub-directory structure was created containing year, feature, month, day, UT range, and observer. Into each lower subdirectory are entered scanned copies of many of the original TLP reports, and a machine readable summary file of each observation. With a total of 1804 TLP reports entered so far manually, this process has been lengthy. However a directory listing has been used to produce records for the histograms used in this abstract, albeit initially without weights. To reduce observational bias and selection effects, observations from two of the most prolific TLP reporters have been deselected, and so too have observations made during the Apollo and Clementine missions. Observations have also been removed if the quoted dates and UT, from the source catalogs, appear to indicate that the Moon was observed in daylight, or was below the horizon, as seen from the observing site. 1313 remaining TLP reports are used in this analysis. Results: Frequency of TLP versus time of the year. All selected reports were placed into appropriate data bins (4 bins per month). The temporal distribution of TLP reports in Figure 1 shows some smoothness in the x-axis direction that we would not expect to see if TLPs occurred (or observers perceived) randomly in time. A slight dip is seen in the middle of the year and this is due to the majority of northern hemisphere observers experiencing poor visibility of the Moon in Summer months – this is confirmed when we use routine nonTLP observations. The most prominent peak (> 2 standard deviations) is towards the end of April, and some of the TLP included here were described by Sir William Herschel as reddish glows in Earthshine [9]. This peak occurs over the time span of the Lyrid meteor shower; however many of the other TLP reports that fall in this slot seem unrelated to what one might expect from meteor impact events in terms of descriptions and non-random geographical locations. Furthermore other higher ZHR showers do not show up in the TLP statistics at all.