Fooling around with lettering. It needs a little tweaking. Some strokes ought to be heavier, maybe. I’m trying to hold onto the energy of my sketch. I’m not sure if I like this yet. Let it sit for a while.
We’ve talked about telling time with sundials and water clocks and hourglasses. Those things are a headache to carry around. Mechanical clocks, like a pendulum clock, wouldn’t be invented until 1637. What if you’re traveling around in ad 800—how do you know what time it is?
One way to tell time was this fantastic little device called an astrolabe.
Wherever you happen to be, if you can see the Sun or the stars, you can tell the time if you’re carrying an astrolabe with you. The main feature of an astrolabe is a flat map of the sky—with the stars and planets on a grid. The grid—called a climate—shows the sky as it appears in your part of the world. It’s circular and fits into a circular frame, called the mater (Latin for ‘mother’). On top of the climate is the rete (Latin for ‘net’), an openwork circular plate with pointers that you can line up to point at the Sun or a specific star on the climate. On top of that is a sighter—a straight arrow kind of piece. All these spin on the same axis. You pick a star, adjust the rete to point at your star on the climate, and hold up the astrolabe and sight the actual star along the sighter. When the sighter lines up with the star, you can read the time with remarkable accuracy. Here’s a video showing how it’s done. This guy even made his own astrolabe. And here’s more.
Here’s a website that explains how to use an astrolabe and even gives you pdfs you can download and print to make your own.
The idea of multiple nesting spheres—each sphere tracking a ‘wandering star’ or planet; the fixed stars; and the motions of the Sun and Moon—is kind of complicated. Astronomers built models of the geocentric universe to try to explain it. These are called armillary spheres.
They were usually made out of brass. Here’s one you can build out of cardboard.
Even though Earth isn’t the center of the universe, the model still works for locating positions of stars as we see them from Earth. Not only was Ptolemy’s data useful for knowing where the stars are and tracking them, but we can also predict where they will be tomorrow or next year. It became possible to know exactly when the Sun will rise and set years in the future. Astronomers could predict eclipses of the Sun or Moon. You can accurately tell the time based on Ptolemy’s data. It was a pain in the neck to carry an armillary sphere around, though. Something more compact was needed.
Back to the beginning of The Western Civ User’s Guide to Time & Space
I did this caricature a few years ago. Obviously I enjoyed painting the hair. I don’t seem to have a copy of the finished piece. Here are some in-progress shots. Gouache on Arches watercolor paper.
As Ptolemy worked out the positions of the stars on a big sphere, he imagined smaller spheres that account for the movement of the Sun and the planets— operating like separate, smaller gears in a giant clock. The amazing thing is, even though Earth isn’t the center of the universe, Ptolemy’s geocentric model is still accurate. Weird, huh? If you ever visit a planetarium, you’ll sit in a round room with a domed ceiling above. At the bottom of the dome, all around the room, is the horizon. The night sky is projected onto the dome with all the fixed stars in their places—they rotate around, just like the real night sky. The planets are also projected onto the dome. The planet projectors operate on a separate gear system exactly like the spheres Ptolemy had proposed.
Here’s some interesting info about planetarium projectors.
Here’s a listing of planetariums so you can find one near you.