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Station 6 and 7 Intervisibility

Copyright © 2003 by Eric M. Jones.
Last revised 21 January 2006.

With thanks to Journal Contributor Bob Fry for asking the question, for his preliminary work on AS17-140-21504, and for his identification of the Station 6 boulders in Gene's Station 7 photo AS17-146-22355.


In Gene Cernan's Station 7 panorama frame AS17-146-22355, the tops of the two major fragments of the Station 6 Split Boulder are just above and slightly to the left of center. More importantly, they are slightly south of the down-Sun direction. Necessarily, the Station 7 should be slightly north of the up-Sun direction as seen from Station 6. The relevant frame from Gene's Station 6 pan is AS17-140-21504. Bob Fry and I have both examined the image with some care and don't see a boulder of the right size that bears obvious resemblance to the Station 7 boulder. Consequently, it seemed appropriate to do a careful determination of bearings of the Station 7 boulder relative to other, identifiable boulders in the area and to background features using (1) photos Gene and Jack took at the two stations, (2) a detail of the area from Pan Camera image AS17-2309, and (3) station locations as marked in Figure 6-3d in the Apollo 17 Preliminary Science Report.

Figure 1 ( 314k ) is a detail from Pan Camera frame AS17-2309 showing the area of interest, extending from Turning Point Rock on the left eastward past the Station 6 Split Boulder to Station 7 and beyond.

Figure 2 ( 203k ) is a labeled version of the same area shown in Figure 1. Marker boulders 'A', 'B', and 'C' are important to the discussion. Note the approximate locations from which Gene's Station 6 and Station 7 pans were taken. Each is marked with an 'x'.

Marker boulders 'A' and 'B' are well to the east of both Stations. 'A' and 'B' can be seen in Figure 3 ( 272k ), which is a side-by-side comparison of labeled details from Gene's Station 6 photo AS17-140-21504 (left) and Gene's Station 7 photo AS17-146-22343 (right). This figure will be discussed in more detail below.

Marker boulder 'C' is southwest of Station 7, as can be seen in Figure 4 ( 272k ), which is a labeled version of Gene's photo AS17-146-22351. Boulder 'C' is beyond the Station 7 boulder in the direction of the center of Henry Crater, making its identification quite easy in the pan camera frame. To help in determining the location of Station 7 in the Station 6 photos, lines are drawn in Figure 5 ( 84k ) from the Station 6 pan site to Station 7, to the Station 7 pan site, and to the three marker boulders. Angular seperations were then measured for later comparison with Gene's Station 6 photo AS17-140-21504. Note that the seperation of boulders 'A' and 'B' as seen from Station 6 is 3.9 degrees.

Figure 6 ( 76k ) is a similar diagram showing the relative locations of Station 6 and the three marker boulders as seen from Station 7. From Station 7, the seperation of boulders 'A' and 'B' is 9.8 degrees.

Before we try to locate Station 7 in AS17-140-21504, additional analysis to confirm the identities marker boulders 'A' and 'B' is appropriate. Namely, we can use the Pan Camera frame to determine differences in bearing of each of the marker boulders as seen from the Station 6 and Station 7 panorama sites. These differences can then be compared with the apparent shift in direction to the boulders relative to a distant background feature as seen from the two sites.

Figure 7 ( 75k ) shows a 7.3 degree difference in bearing of marker boulder 'A' from the Station 6 and 7 pan sites.

Figure 8 ( 78k ) shows a 13.8 degree difference in bearing of marker boulder 'B' from the Station 6 and 7 pan sites.

Let us now return to Figure 3 ( 272k ), which is the side-by-side comparison of similar up-Sun photos from Gene's two pans. In both images, note the dark area - probably an outcrop - near the summit of the most distant peak beyond boulders 'A' and 'B'. The left edge of the dark area provides a reference bearing, labeled '0' in both images. Noting that the spacing of the reseau crosses in the images is 10.3 degrees, we see that the relative bearing of boulder 'A' changes from -3.2 degrees (left of the reference bearing) to +3.5 degrees (right of the reference bearing). The difference is 6.7 degrees, which is in satisfactory agreement with the 7.3 rightward shift expected from Figure 7. Similarly, the relative bearing of boulder 'B' changes from +1.2 degrees to +14.2 degrees, a 13.0 degree difference in good agreement with the 13.8 degree shift expected from Figure 8. In addition, we note that the seperation of boulders 'A' and 'B' as seen from Station 6 is 4.4 degrees, in good agreement with the 3.9 seperation determined in Figure 5 while the seperation of 'A' and 'B' as seen from Station 7 is 10.7 degrees, in satisfactory agreement with the 9.8 degree seperation determined in Figure 6.

Finally, we consider the locations in AS17-140-21504 of the STation 7 boulder and the Station 7 panorama site. Figure 9 ( 78k ) is a detail from 21504. The seperation of 'A' and 'B' is shown as 4.3 degrees while the seperation of 'B' and 'C' is shown as 7.2 degrees. Both are about 10 percent larger than the corresponding determinations in Figure 5. Consequently, the bearings of Station 7 is shown 2.1 degrees left of boulder 'A' and the Station 7 pan location is shown a further 3.0 degrees to the left.

Careful examination of the image does not show anything that looks like the Station 7 boulder at the expected bearing, suggesting that it is not visible from Gene's Station 6 pan site and is obscured by intervening terrain and/or boulders.