Historical Astronomy Project

https://en.wikipedia.org/wiki/Equatorial_ring https://en.wikipedia.org/wiki/Equatorial_ring#:~:text=An%20equatorial%20ring%20was%20an,other%20places%2C%20for%20calendar%20purposes https://sciencedemonstrations.fas.harvard.edu/presentations/equatorial-ring https://people.sc.fsu.edu/~dduke/lectures/lecture2.pdf https://youtu.be/AaWuJHQL-bQ?si=-j6wojPbx4g1rCS0 https://www.fleaglass.com/ads/brass-equatorial-ring-signed-i-sisson-fecit-made-in-london-circa-1720/ https://www.fleaglass.com/ads/brass-equatorial-ring-signed-i-sisson-fecit-made-in-london-circa-1720/ https://cults3d.com/en/3d-model/gadget/equatorial-ring-sundial-dr-strange

When, Who, Where? -Made during 2nd century AD. -Created by astronomer and mathematician Claudius Ptolemy of Alexandria. -Used during the Hellenistic period in ancient Greece. Fundamental to astronomy from Antiquity through the Middle Ages and into the early Modern era. Placed before temples and on solid ground.

The equatorial ring works by being set up vertically in plane of the equator, facing east and west. During the time of the Spring and Fall equinoxes the sun will rise directly in the east and set directly in the west, moving across the zenith. During the majority of the first half of the day the bottom part of the ring will be in the shadow cast by the top half of the ring. For the majority of the rest of the year the sun will illuminate the bottom half of the ring as it moves from further north to further south. There is one thing in the sky that this instrument focuses on, that is the sun. Claudius Ptolomy used the equatorial ring to discover the length of a full year, he did this by measuring how many days in between the equinoxes the bottom half of the ring was illuminated. The measurements that were taken using this tool is the length of a full year.

The purpose of this tool was to tell the exact times on when the spring and autumn equinoxes started. This was important to ancient cultures because it would be useful to use as a calendar as the Gregorian calendar wasn’t yet invented. They probably also wanted to know the equinoxes so they know when they can start their planting seasons and when to end their planting seasons.