Fellow Shadow Watchers,
Most diallists are familiar with the Noon Gap that
occurs on a horizontal sundial with a thick style edge. The fact that the
shadow 'swaps edges' at 6.0am and 6.0pm is also well understood.
I'm currently designing a large horizontal sundial for Longyearbyen at 78° 12'
north to be located on Spitsbergen in the Svalbard Island Group, where it may
well be 'the world's first heated sundial', permafrost and cabling permitting.
The sun at 78°N is above the horizon for several months continuously so the
dial must read for a full 24 hours and its only just now dawned on me that the
corollary of a 'Noon Gap' is a 'Midnight Overlap'. i.e. With a style edge of
any significant thickness the half hours-ish either side of midnight occupy the
same space on a 24 hour dial. Of course a similar situation occurs with an
'overhung' gnomon at Noon at lower latitudes as has been discussed on the SML
before so I should have anticipated this.
Is this a new term for The Glossary or too rare to be worth listing? ;-)
Tony Moss
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