"TIMOLEON", WHERE ARE YOU NOW ?

By Nigel Longshaw


Lunar observation is generally regarded in amateur circles, as a passtime with little reward usually carried out by owners of small aperture telescopes who cannot plunge to the depths of deep space, or budding astrophotographers / CCD enthusiasts looking for a first easy target!

Serious observation of the lunar surface is perceived as an activity in which the amateur can contribute little in the wake of observations carried out by the great observers of the past, close spaceprobe fly by's and humankinds greatest achievement!

It is because so much attention has been given to the Moon in the past that observation of its surface features can be so rewarding even to todays amateur astronomer at any level.

We can now build up a clear picture of numerous features of interest from many different view points and many different viewers! We can record aspects which elude the Orbiters and vice versa, so it is clear that everyones imput is important.

One of the great thrills of serious lunar observation is being able to track down a photograph or observational drawing of a feature observed on a particular evening at ones own telescope. The excitement is even greater if the comparison material has been made under the same lighting conditions and with a similar sized instrument. Details can be compared and confirmed with those recorded, others puzzeled over when aspects of the same features do not correspond or others are missed altogether! Some discrepancies can be attributed to differing orientations of Sun Earth and Moon, others to seeing conditions and telescope used, others merely observer error. These errors are understandable when we consider our restricted terrestrial viewpoint with all its problems of weather, poor air quality etc.and the relatively minute details visible in medium to large aperture amateur telescopes, even a six inch telescope should reach craters a mere mile in diameter under suitable conditions. How then do we explain the loss of an 80 MILE diameter crater!!

On the evening of 1994 December 18th I was observing the waneing Moon with a three inch reflector. The telescope was of good quality but seeing conditions prevented the use of anything higher than X84. I had no special areas noted for observation in my log for that date, but was facinated by the walled plain named Gauss on the north east limb, the interior of which was completely shadow filled. The eastern wall was broken down into a series of brilliant "peaks" and two peakes were protruding above the interior shadows. The observation was made over a 40 minute period, but I returned to the area 25 minutes later to record the greatly diminished eastern wall and central peaks (see Fig. 1).

It is always interesting to record these rapid changes in features due to advancing or diminishing shadows, and as such the observation seemed to be of interest.

Fig 1
Fig 1
Plate 1
Plate 1
The following day whilst checking colongitude values and other data I was trying to locate comparative details in my litrature and consulted Rukl's atlas of the moon.Chart 16 covers the area but shows the western wall of Gauss terminating approximately on a line comensurate with the southern tip of Berosus (large crater to the west of Gauss). This was puzzling, as I seemed to record the western ramparts of Gauss extending further south to a point opposite the centre of Hahn (large crater south of Berosus).

I cross checked with copies of charts by Wilkins and Moore, who both showed a large feature further east than the eastern ramparts of Gauss but appearing to "join" with Gauss at its southern tip. This feature being denoted as "Timoleon" in both cases (see plate 1).

When such discrepancies are suspected it is customary to note the area for future observation in ones observing log, for repeat observation under similar conditions and, if possible, under opposite illumination. This can prove problematical if features towards the centre of the lunar disc are under scrutiny. Whilst observation under rising sun can be easily be secured ,observation of the same feature under opposite illumination generally involves staying up into the "small hours" or setting the alarm and rising early at some unsociable hour. When we are concerned with observation of features in the limb regions, as here, securing observations of a young moon or a couple of days after full prove less problematical and I was therefore able to note several dates for both sunrise and sunset observation under favourable libration, all I needed now was clear skies!

Further research during the early part of 1995 led to Harold Hill supplying Wilkins and Moores description of timoleon which reads:

"A great ring very near the limb to the N.W. of Hahn ?? It is fully 80 miles in diameter with walls bearing peaks of at least 10,000 ft. ,bears a general resemblance to Gauss. On the vast interiorare craters ridges and many hills.Of the craters the largest lies on the west and there are at leastfour more to the south of it. On the northern part is another crater "F" while one of the hills liesalmost exactly in the centre and thus constitutes a central hill. On the outer west is a small crater"

In his recently published work "Mapping and Naming the Moon", E.A.Whitaker lists Timoleon included in appendix L and designates it as one of Schmidts new crater names. Schmidt began his Lunar observing about 1840 and continued for some 34 years. We might then assume that the name Timoleon first appeared during this period.

The next observing opertunity arose on 1995 March 3rd when a slender cresent hung low in the late winter sky. Conditions were not favourable and detail was difficult to make out on the bright cresent. I noted some dark shading and black "spots" indicative of shadow filled craters but little else (see fig 2).

Further results were obtained on 1995 August 11th and 1995 October 9th, both under similar illumination to the first observation and reproduced here in figs. 3 & 4.

Fig 2
Fig 2
Fig 3
Fig 3
Fig 4
Fig 4
An excellent opportunity presented itself on 1996 February 20th (fig 5) when, under sunrise conditions, the sliver of the young moon was observed under surprisingly good seeing conditions and sky transparency. Details generally accorded with the observation in fig. 2 and the "play" of light and shadow seemed to give the impression of a large walled feature in the position of "Timoleon", very puzzeling indeed!

I was spurred on to try and secure observations under sunset conditions but with the region in question more suitably illuminated than when previously observed.

The results reproduced in fig. 6 represent the clearest picture I had to date relating to the area. Conditions were excellent and I decided to study the whole limb region east of Gauss as opportunities for observations of this nature are rare. The area relating to Timoleon was observed, not as a single large enclosure, but as a series of broken ridges, flooded craters and smaller well defined craters. The surface immediately south east of Gauss was broken up into many ridges and valleys, these were very difficult to depict and can only be taken in the drawing as a "representation".

A further study was secured on 1997 Dec. 14th (reproduced in fig. 7) using my eight inch telescope. Whilst this bears a superficial resemblance to that contained in fig. 6, I feel it is a much more accurate account due to the increased aperture used and more favourable illumination / libration. Crater positions and feature interpretations are very often difficult to correlate between observations made on differing dates and moreso with different instruments, this is one of the pitfalls of visual observation, the ability to set down on paper accurate records of features over an extended period is the mark of a first class observer.

Fig 5
Fig 5
Fig 6
Fig 6
Fig 7
Fig 7
From the observational data obtained by myself over a three year period it would seem that under certain illumination and libration conditions evidence for the existence of a walled plain in the position of "Timoleon" is compelling. However under the most favourable presentations the region displays a different appearance, more akin to that of an area of broken ridges and crater forms. With referrence to plate 1 it is obvious there have been discrepencies in the representation of this region in the past. Certain features could be attributed to a degree of copying from one chart to another and its interesting to note that a recent lunar chart given as a "free gift" with an astronomy magazine depicted a large enclosure in the location of Timoleon.Neisons rendition, although crude by todays standards, does show the area comprising open ridges and raised features, more akin to what is observed under sunset conditions with favourable libration.

From personal correspondence with Harold Hill he kindly extracted and supplied data from the J.B.A.A. vol 75 no 2 1965 in which a list of transferred names of lunar features is included. Among these the name Timoleon is dropped and Liapunov substituted. However Liapunov is a crater some 50 miles in diameter at a position 89 deg. east 25 deg. north and nothing like the 80 miles diameter given for Timoleon located approx 80 deg. east 35 deg. north it would seem "Timoleon" has dissapeared !!

I hope the preceding paragraphs will enable readers to realise that they should never take anything for granted, even the owner of a modest telescope has the equipment to "see for themselves" and observe any area of the moon, under differing conditions of illumination, compare their observation with available maps, charts and photographs interpret their findings and draw their OWN conclusions. If this philosophy is adopted then the lunar surface holds a lifetimes observing opportunities.

Article and drawings © Copyright 2000 Nigel Longshaw


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