Unit 02 · The History of Astronomy
Astronomy is the oldest science, and this unit walks the long argument that built it. It begins with the geocentric sky — a reasonable read of the evidence, since you feel no motion and the heavens wheel overhead each night — and traces why it strained against the wandering planets. From Ptolemy's careful geometry to Copernicus's Sun-centered turn, Tycho Brahe's precise naked-eye data, Kepler's three laws of orbital motion, and Galileo's first telescope views of Jupiter's moons and the phases of Venus, mastery means you can explain how patient observation overturned centuries of authority — and see a piece of it yourself in a planet you track across weeks in your own journal.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| The geocentric model & its logic | Dismisses the geocentric model as simply foolish or ignorant. | Says Earth was thought central but cannot say why that was reasonable. | Explains why an Earth-centered sky fit the evidence — no felt motion, the nightly wheeling overhead — and where it strained against the planets' retrograde loops. |
| The shift to a heliocentric model | Cannot contrast the geocentric and heliocentric pictures. | Names Copernicus but treats the switch as mere opinion. | Shows how a Sun-centered model explains retrograde motion more simply, and explains why acceptance came slowly. |
| Tycho's data & Kepler's laws | Does not connect observations to the laws of motion. | Recites one of Kepler's laws from memory without its basis. | Uses Tycho Brahe's precise naked-eye data to justify Kepler's three laws — ellipses, equal areas, and the period–distance relation. |
| Galileo's telescope evidence | Cannot say what Galileo observed or why it mattered. | Names Jupiter's moons but not their significance. | Explains how Jupiter's moons and the phases of Venus were direct evidence against an Earth-centered universe. |
| Tracking the sky & the journal | Accepts claims on authority and leaves the observation journal blank. | Reads about the debate but keeps thin, undated notes. | Tracks a planet's position over weeks under a red flashlight, logging dated sketches, and argues from that evidence rather than authority. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“The geocentric model wasn’t foolish — you feel no motion, and the sky really does wheel overhead every night. It broke on the planets’ retrograde loops. When I tracked Mars over a month in my journal and watched it back up against the stars, Copernicus’s Sun-centered picture explained it far more simply — and Galileo seeing Venus run through phases was evidence authority couldn’t argue away.”
“Ancient people thought Earth was the center because they didn’t know better. Kepler made some laws. Galileo had a telescope, I think.”
You demonstrate this unit by reconstructing the geocentric-to-heliocentric argument and tracking a planet’s motion in your dated sky journal over several weeks, explaining aloud how evidence overturned authority — not a multiple-choice test. A criterion counts as mastered only when you can both trace the historical reasoning and point to the observation that settled it. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.