About a million years ago (21st Feb) I took @haverfordedu Astro101 class to visit Special Collections in the @haverfordedu library to see historical astronomy related books.... here's a thread of some of the cool things we saw....

The first heliocentric model as published by Nicolas Copernicus in "De Revolutionibus Orbium Coelestium" (On the Revolution of Celestial Orbs), 1543.

A geocentric model of the Universe, as published by Sacrobosco in his delightful little book Tractatus de Sphaera (On the Sphere of the World), first published 1230 (this edition 1626 - post Copernicus!).

(PS. That's my little finger - this is a really tiny book).

In Sacrobosco (1230 first publication, this edition from 1626), this neat drawing indicating one of the ways scientists could tell that the Earth was round (definitely not a #flatearth).

One last one from Sacrobosco (1626), which really had many charming diagrams - this one demonstrates how lunar eclipses work.

We looked at a collected works of Galileo, and I was able to find diagrams related to the four main findings he had which supported the heliocentric model and enraged the Catholic church - sunspots, mountains on the Moon, moons of Jupiter, and phases of Venus....

Here's a 1718 reproduction of some of Galileo's sketches of his sunspot observations.

Here is a diagram by Galileo showing mountains on the Moon.

Here's a series of observations of the moons of Jupiter by Galileo. They clearly orbited Jupiter, casting doubt on the geocentric Universe model.

Here's a diagram by Galileo explaining how Venus shows phases. This cannot happen if Venus orbits the Earth, and so is clear evidence of the heliocentric Universe.

That's all the photos I took: we also saw an early copy of Newton's Principia, letters from Albert Einstein, Mary Somerville, Edmund Halley, Williams Herschel, Nathaniel Bowditch and Maria Mitchell, and some materials on the history of the @haverfordedu Observatory.

It was really an awesome visit, and such an amazing resource to see first hand. I am glad we scheduled it before in person classes ended for the semester.