Geology Reference
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F
IG
. 8.19
(
a
,
b
,
c
) Moonset at furthest north, over the silhouette of the
marker stone (Photos by Mark Runnacles, February 9, 2006)
and all I have for that alignment are snapshots taken by my col-
league Bob Graham in a different month, well after moonrise when
it finally cleared the clouds (Fig.
8.22
).
Within the limits of accuracy of the stones, the southerly
events and the northerly moonset appeared to be where they
should be (Figs.
8.19
,
8.20
,
8.21
and
8.22
). But northerly moonrise
was to be a shock - not visible until it emerged from behind the
tower blocks, on a much lower track than predicted (Fig.
8.23
).
Projected back, it met the true horizon at the theoretical rising
point (Fig.
8.24
), but in real life, when it rose above the true hori-
zon, it would have been far to the right of the prediction, almost
out of line with the stone!
Once again the source of the error became clear, once I knew
it was wrong. Under pressure to finalize the calculations, I had
assumed that the rising and setting paths would all make roughly
the same angle with the horizon. I knew that wouldn't be the case
at higher latitudes, but I didn't think it would make a big differ-
ence at the latitude of Glasgow. Instead of doing it graphically,
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