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Mons Piton (published onSelenology, vol 23, n.3, 2004 )

By Cristian Fattinnanziand Raffaello Lena

Geologic Lunar Research (GLR Group)

Introduction

Ina previous paper appeared in Selenology [1] , Boint and Rodenborn described a profile of Mare Imbrium west of Mons Piton.

Mons Piton is an isolated mountain massif reaching a height of 2250 m above the surface of Mare Imbrium.

Several observations of Mons Piton have been made over many lunations by GLR and it is possible to compare the results of these studies.

In this paper we illustrate our results concerning a study of the slope around Mons Piton. The results obtained by us may be compared with data reported in [1].

Instruments and measures

Figure 1: reports Mons Pitonunder a low Sun. This image was obtained on March, 13, 2000 at 18:10 UTby G. Mengoli using a Meade 152 ED refractor.

Figure 2: was obtained by G. Di Iorioon April, 1,2001 at22:00 UT using a Schmidt Cassegrain 20 cm.

Another observation (figure 3) was made by A. Bareson April,2,2001 at 21:00 UT using a Mewlon 25 cm.

The local altitude of the Sun, H and its colongitude, C, were also calculated with the Harry Jaimeson’s Lunar Observer’s Tool kit software.

Furthermore, the scale of the images was obtained which allowed shadow lengths (Lm) to be expressed in km.

For every image considered here the “expected” shadow length (Le)was calculated with the formula:

Le = 2250 / Tan (a)

Where (a) is the local solar altitude above Mons Piton when the images were taken and 2250 is its height.

Comparing the length of the measured shadows (Lm) with the length of the expectedshadows (Le) the apparent incline of thenearby soil (Ia) was estimated.

This apparent incline is calculated with the formula:

Ia=(Le - Lm)Tan (a)

The writersestimate theerror making severalmeasures of the shadow casting points. On this basis the error bar on fig. 1 and 2 is calculated at 1% of the values whereas the error bar on fig.3 is 5% of the value.

FIG.3

On the other hand the effect of the lunar curvature (C) must be taken into account (see figure 4) and it was considered in these measurements.

FIG 4

The “correction factor”considering the effect of the lunar curvaturewas calculated with the formula :

C =1740-(1740)2 - (Lm)2

Where 1740 is the lunar radius and Lm is the measured shadow length.

The degree of incline (Ir), considering the effect of lunar curvature,was calculated with the formula :

Ir = Ia + C

Our results are shown in Table 1.

TABLE 1 (scale of the images 0.445 km per pixel)

Results and discussion

Our data show an interesting incline, considering the correction dueto the lunar curvature. We estimated an incline of -66, -147 and +13 meters at a distance of 9, 25 and 41 km respectively.

It is due to a sloping soil: the shadow length measured will be either longer (downward slope) or shorter (upward slope). The effect of sloping soil is described in [2].

From thiswe estimated the profile of Mare Imbrium west of Mons Piton (Table 2).

TABLE 2

FIG 5

The consistency of the graphed incline (figure 5) suggestsa slight depressionto the west of Mons Piton. By the way our measurement is consistent with our images andthe longest shadow having an upward slope (see fig. 1)seems to be falling on a small mare ridge.We suggest another use of this technique : use shadow length variations to determine a profile of a mare ridge.

Acknowledgement

Many thanks to GLR observers for the images they submitted and to C. Wood for his stimulating discussion.

References

[1] Boint and Rodenborn, Selenology , 2003, vol 22.3.

[2] R. Lena, C. Fattinnanzi and F. Lottero, Selenology, 2004, vol 23.1.

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