Unit III: The Wanderers
CELESTIAL TOWER · UNIT III OF VI
Five bright lights in the ancient sky refused to behave. While every star wheeled past in orderly procession, these five drifted, loitered, and sometimes even walked backward, and the Greeks named them for it: planetes, the wanderers. It took humanity nearly two thousand years to understand what they were doing, and the argument over it redrew our entire picture of the universe. This unit is a detective story, little scholars, and I promise you the geometry is worth it.
Unit Learning Objectives
By the end of this unit, scholars will be able to:
- Find the naked-eye planets in the sky and explain what the word "planet" originally meant.
- Explain retrograde motion geometrically, showing how both the Ptolemaic and Copernican models accounted for it and why the modern understanding works.
- Describe Venus through Maya astronomical records and the transit expeditions, and explain its runaway greenhouse state.
- Narrate the honest history of the Mars canal craze and the "face on Mars," and describe what rovers have actually found.
- Explain how Uranus was recognized as a planet and how Neptune was predicted mathematically before discovery, and state what the IAU planet definition says and why Pluto was reclassified.
In This Unit
Lesson 12: The Naked-Eye Planets
Mercury through Saturn as the ancients knew them: wanderers against the fixed stars, and how to find each one tonight.
Lesson 13: Retrograde & the Model Wars
Why planets seem to move backward, taught as true geometry: epicycles versus perspective, and the telescope evidence that settled it.
Lesson 14: Venus, the Morning Star
The Maya tracked Venus with astonishing precision; centuries later came the transit expeditions and the story of Earth's sister gone wrong.
Lesson 15: Mars, the Red Wanderer
Lowell's canals, the face on Mars, and the rovers that showed us the real planet. Wanting canals did not build them.
Jupiter's moons and Saturn's rings, Uranus observed before it was recognized, and Neptune: the planet found by mathematics first.
Lesson 17: Pluto & What a Planet Is
The 2006 vote heard round the world, what the definition actually says, and why science updating itself in public is a strength, not a scandal.
The Unit III Quiz closes this unit. You will find it, with its download, at the end of Lesson 17: Pluto & What a Planet Is.
What Scholars Will Observe, Practice, and Make
Scholars spot and log two planets in a month, track Venus as a morning or evening star, sketch Jupiter's four bright moons over several nights (Level Two) or track Saturn's steady position (Level One), and work through the retrograde geometry themselves rather than taking anyone's word for it.
Beyond the wanderers lie the lights that never wander at all. In Unit IV we study the fixed stars: what they are, how far away they are, and the true stories behind their names.
From the Celestial Shelf
The printed companions to this unit, from Professor Glimmerwick’s shelf in the shop.
