1. I. Early History of Astronomy
A. Ancient Greeks
1. Used philosophical arguments to explain natural phenomena
2. Also used some observational data
3. Most ancient Greeks held a geocentric (Earth-centered) view of the universe
4. Air, Earth, Fire, Water
5. Aristotle-spherical earth
Geocentric animation

2. I. Early History of Astronomy
a. "Earth-centered" view
1. Earth was a motionless sphere at the center of the universe
2. Stars were on the celestial sphere
a. Transparent, hollow sphere
b. Celestial sphere turns daily around Earth
b. Seven heavenly bodies
1. Changed position in sky
2. The seven wanderers included the
a. Moon
b. Mercury
c. Venus
d. Sun
e. Mars
f. Jupiter
g. Saturn
Aristotle

3. I. Early History of Astronomy
6. Anaxagoras ( BC)-moonlight physics
7. Aristarchus (312–230 B.C.) was the first Greek to profess a Sun-centered, or heliocentric, universe
He also calculated relative sizes and distances of the sun,earth, moon

4. I. Early History of Astronomy
Eratosthenes ( BC): a. 1st to accurately measure the earth’s circumference using a gnomon and the sun.
(250,000 stadia)
b. Error of only ~500 miles

5. I. Early History of Astronomy
9. Hipparchus ( BC):
a. logged ~ 850 star locations and star brightness (6 different magnitudes)
b. Great mathematician
(trig)

6. These are the apparent magnitudes of the bright objects seen in the sky.

7. I. Early History of Astronomy
10. Planets exhibit an apparent westward drift
a. Called retrograde motion
b. Occurs as Earth, with its faster orbital speed, overtakes another planet
Retrograde movement
animation

8. I. Early History of Astronomy
11. Ptolemaic system
(Claudius Ptolemy)
a. A.D. 141, The Almagest
b. Geocentric model
c. To explain retrograde motion, Ptolemy used two motions for the planets
1. Large orbital circles, called deferents, and
2. Small circles, called epicycles
Animation of epicycles and deferents

9. I. Early History of Astronomy
…Ptolemy’s Epicycles and Deferents…

10. I. Early History of Astronomy
…Ptolemy’s retrograde motion…

11. I. Early History of Astronomy
…a model built to explain Retrograde Motion in both a Geocentric and Heliocentric design…

12. RetroLink 2012 Opposition Information
Officially, the current Mars apparition begins with the 4 Feb 2011 conjunction—when Mars is in the same direction as the Sun from the point of view of an Earth-bound observer.
For this apparition Mars opposition will occur at 20:35 03 March 2012 UT. Mars will have a visual magnitude of -1.23, a size of about 13.9 arcseconds and be about 1.66 AU away from Earth. At opposition, it will be at coordinates (J2000) 11h06m, +10°21' in the constellation of Leo. Note that a waxing gibbous Moon will be about 40° to the west of Mars so scattered light could affect your observing. Mars will appear as a bright red-orange object that should rise at about the same time the sun sets (and set at about the same time as the next sunrise). The season on Mars will be late spring in the northern hemisphere and late autumn in the southern hemisphere; LS=78.3° for those familiar with that notation. At opposition, the entire visible disk of Mars is illuminated; it is in its full phase, much like a full moon. Before and after opposition, it will be in a gibbous phase; it can never have a crescent phase since Mars is further away from the Sun than Earth and thus can never be between Earth and the Sun
RetroLink

13. I. Early History of Astronomy
B. Birth of modern astronomy
s and 1600s
2. Five noted scientists
a. Nicolaus Copernicus (1473–1543)
1. Concluded Earth was just a planet
2. Constructed a model of the solar system that put the Sun at the center, but he used circular orbits for the planets
3. Heliocentric Solar System
4. Ushered out old astronomy
5. De Revolutionibus

14. I. Early History of Astronomy
b. Tycho Brahe (1546–1601)
1. Precise observer
2. Tried to find stellar parallax: the apparent shift in a star's position due to the revolution of Earth
3. Did not believe in the Copernican system because he was unable to observe stellar parallax
Animation of different systems

15. I. Early History of Astronomy
Tycho Brahe (1546–1601)
4. Great instrument maker
Cassiopeia…1572
Tycho’s Supernova
Tycho Crater, about 85 kilometers across, is clearly visible on our Moon's surface. The freshness of the crater and the rays of material radiating from it suggest that this is a young crater; there has been little time to erode it. Tycho Crater appears close to the southern polar region of the Moon. The circular crater is surrounded by a bright ejecta blanket. Rays of ejecta extend across the lunar surface.
Tycho Crater on the Moon
The Quadrant

16. I. Early History of Astronomy
c. Johannes Kepler (1571–1630)
1. Ushered in new astronomy
2. Planets revolve around the Sun
3. Student of Tycho Brahe
4. Strong mathematician

17. I. Early History of Astronomy
5. Three laws of planetary motion
a. Orbits of the planets are elliptical
b. Planets revolve around the Sun at varying speed
(Faster at perihelion…..slower at aphelion)
c. There is a proportional relation between a planet's orbital period and its distance to the Sun (measured in astronomical units (AUs)—one AU averages about 150 million kilometers, or 93 million miles) P2=a3

18. I. Early History of Astronomy
…What is an Ellipse?...

19. I. History of Early Astronomy

20. I. Early History of Astronomy
..the properties of an ellipse…

21. I. Early History of Astronomy
Kepler’s 3 Laws:
#1: All orbits are elliptical……………..e is eccentricity
As “e” approaches 0, the orbit becomes more circular!
Icarus’ orbit

22. I. Early History of Astronomy
Kepler’s 3 Laws:
#2: Equal Area Law
animation
This implies a planet moves faster at perihelion and slower at aphelion!

23. I. Early History of Astronomy
Kepler’s 3 Laws: #3: P2 (years) = a3 (AU)
For Earth: Period is 1 year
a is 1 AU
Therefore (1)2=(1)3
For Jupiter: Period is years
a is 5.20 AU
Therefore: (11.86)2 = (5.20)3
140.6 = 140.6

24. I. Early History of Astronomy
…Kepler’s 3 Laws of Planetary Motion…

25. I. Early History of Astronomy
d. Galileo Galilei (1564–1642)
1. Supported Copernican theory
2. Used experimental data
3. Used an astronomical telescope in 1609
4 Galilean Satellites:
Io, Europa, Ganymede, Callisto

26. I. Early History of Astronomy
4. Galileo's discoveries using the telescope
a. Four large moons of Jupiter
b. Planets appeared as disks
c. Phases of Venus
d. Features on the Moon
e. Sunspots and sun’s rotation

27. I. Early History of Astronomy

28. I. Early History of Astronomy
5. Tried and convicted by the Inquisition…died under house arrest
6. In 1992, 350 years later, Pope John Paul II officially declared Galileo innocent.
7. Galileo died, blind and under house arrest, on January 8, 1642.
On Christmas Day of that same year, born was…………

29. I. Early History of Astronomy
e. Sir Isaac Newton (1643–1727)
1. Law of universal gravitation
2. Proved that the force of gravity combined with the tendency of a planet to remain in straight-line motion results in the elliptical orbits discovered by Kepler
3. 3 laws of motion
(inertia…1st law)
4. Mass vs Weight
5. Principia
Halley’s Comet
Orbital animation

30. I. Early History of Astronomy
…What is Gravity?...

31. I. Early History of Astronomy
…What is Gravity?...

32. I. Early History of Astronomy
…What is gravity?...

33. I. Early History of Astronomy
…What is Gravity?...
Zero G drink

34. I. Early History of Astronomy
…Orbital Movement…
Link

35. I. Early History of Astronomy
…A brief timeline review………