From Ptolemy to Webb
On the fall equinox at St. John’s College, the Ptolemy Stone captures a celestial moment: a bronze ring, tilted to the latitude of Annapolis, through which the Sun casts a shadow exactly along its center line at 2:20pm. The design echoes the ancient armillary spheres described in Ptolemy’s Almagest, where nested circles modeled the heavens and guided centuries of observers. Students who gather at the Stone stand in a lineage stretching from Alexandrian spheres to the great observatories of Europe. Today the James Webb Space Telescope extends that lineage to the edge of the universe, and soon the Vera C. Rubin Observatory → in Chile will map the southern sky every few nights, revealing cosmic change in real time. From bronze ring to billion-dollar arrays, we still trace order in the sky.
Ptolemy’s Spheres →
Hubble Tension →
The Ptolemy Stone, St. John’s College, September 2025. Photo by author.