Measurement
The Solar Ring Clock
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This sundial tells time using sunlight passing through numbered openings in a ring.
As the Sun moves across the sky, light shines through a different number and projects it onto the central surface, showing the approximate hour.
Additional Information
This style is related to the “armillary sphere” sundial, a design going back to ancient Greek and Chinese astronomy.
The ring has to be tilted to align with Earth’s axis for the time markings to stay accurate through the seasons.
As the seasons change and the Sun’s path shifts, the bright spot’s height on the ring shifts too — some ring sundials use that to show the date as well as the time.