Ancient to Modern Astronomy Ptolemy 85 A.D. to Newton 1727 View retrograde motion View retrograde motion

Ptolemy (85 A.D A.D.)  Ptolemy modified the geocentric model to account for the retrograde motion of planets  The "solution" to retrograde motion came in the form of a mad, but clever proposal

Ptolemy (85 A.D A.D.)  "Epicycles", and the concentric spheres to which they were attached were termed the "Deferents”  Centers of the epicycles executed uniform circular motion as they went around the deferent at uniform angular velocity, and at the same time the epicyles (to which the planets were attached) executed their own uniform circular motion

Ptolemy (85 A.D A.D.)

Claudius Ptolemaeus (Ptolemy) (85 A.D A.D.) At first, not widely accepted because scientists thought the model to be too complicated At first, not widely accepted because scientists thought the model to be too complicated Although the geocentric model with epicycles did explain the motions of the planets better. Although the geocentric model with epicycles did explain the motions of the planets better. Important in terms of predicting astrology and fate. Important in terms of predicting astrology and fate.

Later refinements (2nd century B.C.) Hipparchus: Placing the Earth away from the centers of the “perfect spheres” Ptolemy: Further refinements, including epicycles

Epicycles The Ptolemaic system was considered the “standard model” of the Universe until the Copernican Revolution. Introduced to explain retrograde (westward) motion of planets

Epicycles (SLIDESHOW MODE ONLY) View retrograde motion Video from Movies

The Copernican Revolution Nicolaus Copernicus (1473 – 1543): Father of the Heliocentric Universe (Sun in the Center)

Nicolas Copernicus ( ) Polish cleric first proposed the heliocentric model Wrote the book De Revolutionibus and stashed it under his mattress Proposed all planets including Earth revolve around the Sun Circular orbits at constant velocities Copernicus’ model was the best to date but still had problems accurately pinpointing the position of the planets

Copernicus’ new (and correct) explanation for retrograde motion of the planets This made Ptolemy’s epicycles unnecessary. Retrograde (westward) motion of a planet occurs when the Earth passes the planet. Explanation of Retrograde Motion

Explain the difference between the geo- and helio-centric models of the solar system. Earth- centered Sun- centered

Galileo Galilei (1564 – 1642) Invented the modern view of science: Transition from a faith-based “science” to an observation-based science. Greatly improved on the newly invented telescope technology. (But Galileo did NOT invent the telescope!) Was the first to meticulously report telescope observations of the sky to support the Copernican Model of the Universe.

Major Discoveries of Galileo (2) Surface structures on the moon; first estimates of the height of mountains on the moon

Major Discoveries of Galileo Moons of Jupiter (4 Galilean moons) Rings of Saturn (What he really saw)

Major Discoveries of Galileo (3) Sun spots (proving that the sun is not perfect!)

Major Discoveries of Galileo (4) Phases of Venus (including “full Venus”), proving that Venus orbits the sun, not the Earth!