by Raffaello Lena, Piergiovanni Salimbeni, Cristian Fattinnanzi, Giorgio Mengoli
 
Geologic Lunar Research group (GLR)

Introduction
A paper recently appeared in this Journal [1] proposed the presence of possible domes in crater Ptolemaeus.
The problem with visualizing domes in Ptolemaeus is that they are emplaced on a rolling plains material called the Cayley plains.
This undulating topography makes discerning buried craters from ordinary reliefs rather difficult. By the way our hypothesis on the presence of domes in Ptolemaeus was  further suggested by the finding of domes in the Ranger imagery [1-2].
To ascertain if other structures could be ascribed to lunar domes morphology the Geologic Lunar Research group (GLR) set out to coordinate its team of observers for the target date of january 18, 2002 and march 21, 2002.
 

Observations
Our group worked by using the Internet as a communication platform in real time coordinating observing event.
Our observations are reported  in Figures  1-7.
For each observations considered here, the local altitude of the Sun, H, and its colongitude, C, were calculated with the Lunar Observer's Tool kit software. From the shadow lenghts and the local solar altitude, the heights of the features casting the shadows were also estimated with the same software.

The agreement between visual observations and the corresponding images is very good. The images provides further evidence of these features which are difficult to discern in different lighting conditions. The reported dome-like features (Table 1) appear to be hemispherical, having a gentle slope, but are lacking in other surface features on the top.
 

Discussion:
On the floor of Ptolemaeus there are several structures  that are not domes, as they have an irregular shape and major/minor axis ratios of greater than 2. These are likely hummocky terrain or subdued crater walls due to the Imbrium ejecta inundation. However, the numbered features are all of dome like morphology, and have major/minor axis ratios of less than 2. Their  positions and diameters  are identified in table 1.

Table 1

Feature     Eta             Xi         latitude(°)     longitude(°) Diameter  Km
 
1             -0.1540     -0.0579         -8.86             -3.00                 5
2             -0.1525     -0.0517         -8.77             -3.36                 6
3             -0.1590     -0.0599         -9.15             -3.48                 4
4             -0.1530      -0.0619         -8.80            -3.59                 4

Using our available images we estimate for features 1-2 a height at about 100 meters.
These features are of low height and angle of inclination, making them difficult to identify when distant from the terminator.

Their morphology is in agreement (as best we can tell) with  the Westfall criteria  [3].
More observations of these  structures  are needed to study their origin. This report also demonstrates that lunar domes are difficult features for the lunar observer. They require extreme patience and specific conditions of lunar solar altitude.

Our hypothesis on the presence of possible domes is further suggested by the finding of domes in Ptolemaeus in the Ranger imagery [1-2].
It could be  a definite indication that, at some time in its geologic history, the crater Ptolemaeus  was an area where the intruding lavas found release to the surface.

Acknowledgments:
The authors gratefully acknowledge M. Cicognani and F. Padulosi  for their contribution to this paper.
 

 References:
[1] Lena R., Salimbeni Pg., Douglass E.,  Santacana G., On the presence of possible domes in Ptolemaeus: a preliminary report. Selenology, vol 20, n.3, 2001.
[2]  Ranger IX Photographs of the Moon. NASA SP-112. U.S. Government Printing Office: Washington, 1966.
[3] Westfall J., A generic classification of lunar domes. JALPO, 18, 1964.

Captions to figures:
 

Figure 1: Pg. Salimbeni  on January 18,  2002 at 18:20 UT, seeing I Antoniadi scale; SCT 200 mm f/10 at 300x. H =4.18° over  Ptolemaeus  C= 5.89° .
 

Figure 2: R. Lena on January 18,  2002 at 18:40 UT, seeing II-III Antoniadi scale; SCT 250 mm f/10 at 250x. H =4.35° over Ptolemaeus  C= 6.07° .
 

Figure 3: M. Cicognani on August 26,  2001 at 19:30 UT, seeing III Antoniadi scale; Cassegrain 410 mm  f/17 at 284x. H =2.26° over  Ptolemaeus  C= 4.31° .

Figure 4: G.Mengoli , on March 21,  2002 at 18:00 UT, seeing III Antoniadi scale; SCT 250 mm  f/10 CCD Starlight Xpress HX5,
software  AstroArt v2.0 (media-highPass-LowPass). H =2.14° over  Ptolemaeus  C= 3.72° .

Figure 5: C. Fattinnanzi , on March 21,  2002 at 18:40 UT, seeing III Antoniadi scale. Newton 200 mm f/6 and  webcam Vesta .
H =2.47° over  Ptolemaeus  C= 4.06° .

Figure 6: C. Fattinnanzi , as preceding image.

Figure 7: R. Lena on March 21,  2002 at 20:30 UT , seeing III Antoniadi scale.  Refractor 10 cm f/15 at 250x. H =3.48° over  Ptolemaeus  C=5.08 ° .