Figures of Early Astronomy Texts

James Hedberg

City College of New York,

Dept. of Physics

"Aren't they all wrong?"

-anonymous

"Philosophy of science is about as useful to scientists as ornithology is to birds."

-Richard Feynman

California Condor Wild Populations

Data from the Center for Biological Diversity

Back to the books

Ptolemy - The Almagest

Claudius Ptolemy: a sketch from 1584 (he died in 170)

That the Heavens are Spherical and Move as a Sphere
That the Earth is Spherical as a Whole
That the Earth is small compared to the Heavens
That the Earth is in the Middle of the Heavens
That the Earth does Not Move at All

"Sun, stand still over Gibeon, and you, moon, over the Valley of Aijalon."

-Joshua

Nikolaus Copernicus - de Revolutionibus

That the Heavens are Spherical and Move as a Sphere
That the Earth is Spherical as a Whole
That the Earth is small compared to the Heavens
Maybe the Earth is NOT in the Middle of the Heavens?
Maybe the Earth does Move?

Copernicus's hand drawn system of the world.

From the original manuscript of De Revolutionibus

Close up: Note the hole in the center where the compass needle has poked through the page.

Here we see Copernicus' hand drawn system of the world. One can imaging him placing the compass needle in exactly the same spot 8 times, and then carefully tracing out the resulting circle.

It's hard to say what was the original thought process that lead Copernicus to explore the notion of a Heliocentric solar system. He didn't leave many notes behind and what we do have, are mostly legal and official documents related to his duties as a physician and canon. From his scientific work, we can be certain that Copernicus loved circles. His main complaint with the Ptolemaic system was that in order to explain the observed change in speed of planets, the geocentrics had to introduce the dreaded 'equant'. Getting rid of the equant was Copernicus' prime motivations in building his new system.

What improvements does Copernicus' system make?

Better predictions? - no
Simpler math? - not really
Makes more sense from a physical point of view? - kinda

In this arrangement, therefore, we discover a marvelous symmetry of the universe, and an established harmonious linkage between the motion of the spheres and their size, such as can be found in no other way.

-Copernicus

Astronomy is stuck

Parallatic to measure the altitude and azimuths

Tycho Brahe

Kepler - Mysterium Cosmographicum

Why were the planetary orbs arranged as such?

References

Primary

Ptolemy's Almagest
Copernicus, De Revolutionibus
Kepler, Mysterium Cosmographicum

Secondary

The Almagest: Introduction to the Mathematics of the Heavens, Ptolemy, Perry & Donahue
The Copernican Revolution, Thomas Kuhn
The Book Nobody Read, Owen Gingrich
Kepler's Geometrical Cosmology, J.V. Field

Other

Tycho Brahe's Description of his instruments and scientific work, Raeder, Stromgren, and Stromgren, 1946