A Shadow Stick in the Bahamas

This just in from Dick Forte in the Bahamas…

Tristan,

Here is a Gooley-inspired sun dial in the southern Bahamas, just inside the tropics, 74 56.9 w, 23 06.5 n. (I call it a Gooliation, an elision of Gooley with inspiration or celebration.)

The conch shells with blue tops were put down in November on the hour (eastern standard time) at the top of the shadow made by the gnomon. The shells with the green tops were similarly placed this April (also on EST not EDT). Shells with the same hour are linked with white markers. There are more greens than blues because the shadows for the blues in the morning and evenings got too long. Ill send a few more shots by following emails.

Thanks for the idea. It was fun creating it and hopefully a few more lines will be laid down in the future.

Dick

PS. I cant figure out why the November shells are in an arc while the April ones seem to be in a straight line.

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Thanks Dick, what a joy to receive pictures of a shadow stick from the Bahamas.

From my email reply:

The difference between straight and curved arcs is to do with how close to the equinox you are. Lines appear straighter the closer to an equinox you are and more curved the closer to a solstice.

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