1. The Copernican Cosmos

2. -80 epicycles in the Ptolemaic system -34 in the Copernican system
Ptolemaic Universe: “Epicycles Upon Epicycles”
-80 epicycles in the Ptolemaic system
-34 in the Copernican system

3. Copernicus:
Application of Occam’s razor? Yes. Epicycles overpopulate the heavens. Overly complex system.

4. Three incorrect assumptions
Earth was the center of the universe
Uniform circular motion in the heavens
Planets made from a perfect, unchanging substance not found on the Earth (quintessence).

5. Copernican Revolution
Copernican Revolution is a term which applies to the transition from a geocentric cosmological model to a heliocentric model.

6. Copernican model

7. Tycho and Stellar Parallaxes
Bio ( )
-scientist (astronomer)
-the nose

8. Sextant

9. Sextant
-measures the angles between two objects, generally a celestial
object and the horizon

10. Modern sextant

11. Why is the sextant important to science?
Brahe used them for stellar measurements
Better navigation for ships
Observation of a stellar parallax for Tycho? No, a parallax is not observed until 1838 with the help of a strong telescope.

12. Parallax
Illustration

13. Tycho’s Cosmological Model

14. Tycho’s Cosmological Model
Tried to reconcile Ptolemaic and Copernican systems
the five planets orbit the Sun, while the Moon and the Sun orbit the stationary Earth.
Sphere of fixed stars remained. Brahe supported his model by observing that the stars
did not shift (i.e., he could not observe parallaxes).

15. Other Contributions to Science
Studies on the new star of 1572
Studies on comet of 1574
Both challenge the veracity of the Aristotelian
contention that the heavens are inalternable,
incorruptible.

16. Tycho’s cosmology merges the Ptolemaic and Copernican systems
Tycho’s cosmology merges the Ptolemaic and Copernican systems. Geocentric universe with the planets revolving around the sun.
Why? He could not observe a stellar parallax (shifting of the stars) which would involve great distances of empty space which was an implausible notion (horror vacui-nature abhors a vacuum).
Made and used a sextant for stellar measurements. Sextant has practical uses for seafaring.
Discovery of star (nova) of 1572 and comet of 1574 turns Aristotle’s thesis of the inalterability of the heavens on its head.

17. Assumption of uniform circular motion (planetary circular orbits).

18. Johannes Kepler

19. Kepler’s Three Laws of Planetary Motion
-First Law. Orbit of every planet is elliptical, with the sun as one of the foci.

20. Kepler’s Three Laws of Planetary Motion
-Second Law. The radius vector (of a planet) traverses equal areas in equal times.

21. Kepler’s Three Laws of Planetary Motion
-Third Law. T 2 = R 3
the square of the time of one orbital period (T2) is equal to the cube of its average orbital radius (R3).
Problem: What is Venus’s average distance from the sun? Well, we know Venus takes earth days to orbit the
sun. Venus’s orbital period then would be 224.7/365 or.61 earth years. Since T 2 = R 3, then
.612=R3 or
.3721= R3
3√ = 3√ R3
.71926=R
Which would be AU (astronomical units). If one AU for earth
is 93,000,000 miles, then Venus’s average distance would be
66,859, miles.

22. Next time, class presentation