GASSENDI

17.5S BY 39.9W

LUNAR TRANSIENT PHENOMENA

DAVID O. DARLING

Mare Humorum: "On the north 'shore ' is one of the most beautiful and intensively observed lunar formation, the walled plain Gassendi, about 55 miles in diameter. It has a curious lop-sided appearance and its walls are quite high and complete except on the extreme south where there is a gap. It seems that in the remote past the fluid material of the Mare Humorum destroyed this part of the south wall of Gassendi and flooded the south part of the floor. At the center is a splendid group of mountain peaks, the highest of which rises to 4000 feet. On the south-east part of the floor is the remnant of what was probably once a nearly concentric interior ring. Gassendi is notable because of the variety of details on its interior, among which are about 30 or 40 clefts. Two of the most prominent of these diverge from the central mountains over the floor in a south-west direction. Associated with these are two craterlets that are very bright at full moon. These and other clefts in the south-west part of the floor are easily visible in a four inch telescope but the others that are on the east half of the interior need large apertures to be seen. They criss-cross or run parallel in a complex manner and cannot all be seen on any one occasion. Good seeing, the right angle of illumination and favorable libration are essential for their successful visualization. The cleft system has been charted by different observers and there is a strange diversity among the different delineations. In fact, it has been said: "Every Man his own Gassendi". The north wall of Gassendi is intruded upon by the crater Clarkson and just to the east of the wall of Gassendi is sliced through by two prominent gaps that continue across the floor as two parallel clefts. On the east wall is a curious crater-like depression from which extends on the outside in a south-east direction the Percy Mountains defining the north-east border of the Mare Humorum." The Moon Observer's Handbook by Fred W. Price.

Many observers have reported lunar transient phenomena in this crater to include the notable Patrick Moore who was the founder of the term TLP.

Lunar Orbiter 4 Photograph (N.A.S.A.) LO4-143h2

Crater Gassendi located in lower right hand of above image.

Lunar Orbiter 5 photograph (N.A.S.A.) 5LO-178

This excellent photograph shows the floor of Gassendi and gives one of the best photographic examples to show the multiple rills and cracks crossing the crater floor better known as Gassendi Rimae.

The sunrise terminator crosses over the crater Gassendi on the 11th day of lunation and sets on the 25th day. The most significant jump takes place on day 11 but no other days show any significant activity.

When examining the reported events by just reddish events again we find that the vast majority occur on the 11th day of lunation.

It's unclear as to why the months May and September should show higher activity periods. Further research will have to be done to try and determine the reason behind this.

When examining the data by L.T.P. types it found the most dominate reported is the reddish events.

Gassendi L.T.P. Plot

The libration plot presented above shows there to be many pockets of activity with much of the libration plot being void of any activity at all. The most active quadrant is the southeast followed by the southwest quadrant.

Gassendi Total L.T.P. Plot

0	2	2	2	2	1	1	0
0	2	3	0	0	0	1	1
1	1	0	1	2	0	0	2
0	0	1	2	1	1	0	0
1	1	0	0	1	0	0	2
0	2	0	0	2	1	0	0
1	0	1	1	0	0	0	0

When examining the the break down of data into 52 bins, with each bin consisting of 4 squares no significant pattern develops as it did with the Aristarchus data.

The drawing below was done using my 12.5 f 5 Newtonian reflector with a 10mm eyepiece.

This drawing shows the v shaped formation seen by myself. This closely matches the same shape that was reported by Patrick Moore on 30 April 1966. He detected this red area using the Moon Blink device.

Conclusion: When examining the data in this study it clear that the most active phenomena is the reddish event. This reddish event is reported mostly during sunrise on the feature. This may indicate that something is causing the color effect possibly such as dust levitation within the crater itself. It's unclear why so many events should be documented when the sun is rising on this feature but none are reported when sunset takes place. This is very strange in that if dust levitation was the cause of this phenomena it should be observed at both sunrise and sunset time. Logic dictates that this phenomena should follow the sunrise and sunset terminator. Libration effects also appear to not be the cause for lunar transient phenomena. When placing the libration plots into the 52 bin spread sheet no significant grouping of the events took place. Clearly more study needs to be completed on this crater to give us a better understanding of what is truly taking place here.