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Hello Robert.

Your imagination is indeed worthy of a Hollywood fantasy film script,
I am sure you would find a move to the West Coast a profitable one ;-)

The trouble is that without a time for the photo, you are in the end
dependent of what is essentially a lunar to give you longitude, which
results in an error of the order of 50 miles in longitude

My more prosaic offering was to envisage three acacia trees standing
in a triangle. Ropes are brought from each tree and tied together at
the centre. A plumbline is hung from the join between the three ropes.

There are (in the Southern part of the Sahara desert) two days a year
when the sun is directly overhead. At that moment, the shadow of the
three ropes on the ground will appear centered like the cross hairs
of a telescopic sight on the shadow of the plumb bob on the ground.

The moon rising (or setting) could be in the sky and a plate, with
water in it, reflecting the top of the moon, could be carefully
placed on the ground.

This information would be sufficient to give the year and day and
narrow down the time to within a few minutes from the altitude of the
moon, but I can see no way to improve on that, except that our
soldier writes the time on the back of the photo, or there is a clock
in the photo somewhere.

This scenario would appear to have been feasible in 1943, which was
the last year of the desert campaign.

Thanks again for your thoughts

Geoffrey

   

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