ASTR 1000 Lecture Notes - Lecture 5: Deferent And Epicycle, Orbital Period, Semi-Major And Semi-Minor Axes
19 Jun 2018
School
Department
Course
Professor
Class 5 & 6
Geocentric Models: Geo meaning earth, centric meaning at the centre. A model of the solar
system that holds that earth is at the centre of the universe and all other bodies are in orbit around
it. The earliest theories of the solar system were geocentric. The idea of circles. The moon moves
faster than the sun, and the celestial sphere moves slower
than the sun.
-Problems appeared when you put the planets into this
theory:
-Mercury and Venus always stayed near
the sun
-Mars, Jupiter and Saturn experienced
prograde and retrograde motion.
- Mercury and Venus are in Orbits
INSIDE the earth, the others are
OUTSIDE the orbit.
Ptolmey: Idea is the planet is on an epicycle, moves counterclockwise on the epicycle but the
deferent stays put. Prograde motion outside of loop, retrograde loop inside loop.
- Venus never gets more then a 46degree angle away from the sun
Heliocentric Model - Helio meaning “Sun God”, centric meaning putting the sun at the centre of
things. A model of the solar system that is centred on the sun, with Earth in motion about the sun.
Big 5 astronomers - Copernicus, Gallileo, Tycho Brahe, Kepler, and Newton
Copernicus - he asserted that earth spins on its axis and, like all other planets, orbits the sun. Not
only does this model explained he observes daily and seasonal changes in the heavens, as we
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Geocentric models: geo meaning earth, centric meaning at the centre. A model of the solar system that holds that earth is at the centre of the universe and all other bodies are in orbit around it. The earliest theories of the solar system were geocentric. The moon moves faster than the sun, and the celestial sphere moves slower than the sun. Problems appeared when you put the planets into this theory: Mercury and venus always stayed near the sun. Mars, jupiter and saturn experienced prograde and retrograde motion. Ptolmey: idea is the planet is on an epicycle, moves counterclockwise on the epicycle but the deferent stays put. Prograde motion outside of loop, retrograde loop inside loop. Venus never gets more then a 46degree angle away from the sun. Heliocentric model - helio meaning sun god , centric meaning putting the sun at the centre of things.
