Open during daylight hours. Mostly.
The daylight
department.
A small office with one employee.
Raise the fin. Let the sun do the work.
—:—
Today in Philadelphia
—:— solar time
Made for 39.95° north
A little paper. A little astronomy.
The dial keeps solar time. Your clock also keeps time zones and daylight saving.
A note from the timekeeper
The folded fin points toward true north. Its upper edge rises at Philadelphia’s latitude, so its shadow crosses the printed solar-hour lines as Earth turns.
Clock time and solar time differ because of longitude, Earth’s orbit and axial tilt, and daylight saving. The two readouts describe the same moment. The scrubber follows the actual Philadelphia day, including the shorter and longer days when the clocks change.
This is a calculated, clear-horizon shadow for central Philadelphia, using standard atmospheric refraction. Buildings, clouds and local weather are left outside the department. Near the horizon, the shadow can extend beyond the paper.
The dawn stop is 12 minutes after calculated sunrise; evening is 25 minutes before sunset. At night the sun casts no shadow, even though the dial still sits in the light of your screen.
Solar calculations follow NOAA’s published method ↗, checked against U.S. Naval Observatory positions ↗. All calculations run here; no location permission or weather service is needed.