Eclipse Sundial August 21, 2017
at latitude 44.480°, longitude 73.210° W
Max. coverage: 68% Time of max. coverage: 2:40 pm EDT
This is an unusual sundial that tells time only during a solar eclipse, and only for the location for which it was designed.
To tell time during eclipse, set paper flat on the ground, oriented to true north. (To cheat, you can adjust the paper to match the sun at one of the time readings)
Project the sun’s image on to the dial using a pinhole card. The image will be small from a pinhole, but larger from binoculars. Visit staging.timeanddate.com/eclipse/make-pinhole-projector.html to learn how to do this safely. Rotation will be most rapid near the eclipse maximum.
As the moon crosses in front of the sun, the sun’s crescent will rotate. Read time from the line that matches the sun’s crescent tips.
Curiously, the dial rotates clockwise for locations south of totality, and counter-clockwise for locations north of totality.