Chapter 2 - History

Lets See What the Greeks Knew (THIS IS NOT INYOUR TEXT!)

Geocentric - earth centered
Wanderers - planets
1. sun
2. moon
3. Mercury
4. Venus
5. Mars
6. Jupiter
7. Saturn

on the celestial sphere

Aristotle (384 - 322 BC)

1. Astronomy - spherical earth
2. Chemistry - 4 Basic elements
3. Physics - motion


Aristarchus (312 - 230 BC)

1. sun centered
2. calculated dist to sun and moon
3. calculated sizes of sun and moon- he was wrong but on the right track


Eratosthenes (276 - 194 BC) (OH)

1. calculated circumference of earth - ~2% error


Hipparchus (~100 BC)

1. star catalog ~ 800 stars
2. determined brightness of stars - 6 magnitudes
3. calculated length of year within 4 minutes
4. predicted eclipses w/in hrs.


Ptolemy ( 141 ) - Almagest

1. earth centered - Geocentric image
2. circles for orbits
a. deferents
b. epicycles

3. retrograde motion (OH)

Accepted for ~13 centuries - the power of the RomanC.C.

Retrograde Motion Movie


Why did astronomy change? $$$$$$$$$$$$$$$$$$$$$$

What is happening in the world at this time?

Nicolas Copernicus (1473 - 1543)

Polish Cleric - religious man
Politically correct - thought his book would cause trouble; so he dedicated it to the Pope
De Revolutionibus, Orbium Coelestium
On the Revolution of the Heavenly Sphere
1. Earth was a planet
2. Sun was in the center - heliocentric
the most talked about but least read book in history?
it still used:
1. circles for orbits
2. epicycles
3. does not really explain retrograde motion
But it does:
1. determine the distance to the planets
2. determine the period of the planets (He got 6)
3. allows to identify the geometric arrangements of the solar system

1600 - Giordano Bruno - burned at the stake

Tycho Brahe (1546 - 1601)

1. Best naked eye astronomer of all time
2. built the best instruments
3. used research teams - get the best help & giveit the hardest problems
4. He canít find stellar parallax (OH)
5. ultimate party animal - Can you really have to muchFUN? -- no nose & real jerk
Johannes Kepler (1571 - 1630) Last astrologer/astronomer- celestial harmonies
God as mathematician
Keplerís 3 Laws of Planetary Motion
1. Ellipses (OH 1 & OH 2)    Aphelion and Perihelion
2. Equal Areas
3. p2 = d3 (see Table 2-3 do these on your calculator - read the box to the left too.)needs the Astronomical Unit (AU) - distance from Earth to Sun150 x 106 km

Galileo Galilei (1564 - 1642)

Thought vs. experiment

Falling objects - LT of Pisa

Using a telescope - he did NOT invent it, so who did?

1. 4 satellites (moons) of Jupiter - I Eat Cream Gravy
a. determined their period
b. dispelled belief that Earth would leave the       Moon behind
Galileo Data        Actual picture

2. Planets are disks - Earth like?

3. Venus has phases like the moon phases indicate an orbit inside the Earthís

4. Moon is not smooth

a. mountains
b. craters
c. plains - mare - "seas"

5. Sunspots - sun is not "pure"

a. determined rotational period

In 1616 the RCC declares the Copernican system illegal! (Yes, this will work)

Wrote Sidereus Nuncius ( The Starry Messenger)b/c it didn't discuss philosophical implications and was in Latin the RCC let it slide

Wrote Dialogue of the Great World Systems in Italian

He was exonerated by the RCC* in 1992 - so they issued a stamp! Anything for a buck

*Really Cash Crazy

What else and who else is around at this time?

Pascal, the Ninja Turtles

What is the Rest of the world doing?

Isaac Newton (1643 - 1727)

A. Laws of Motion
1. Inertia
2. F = ma
3. Action = Reaction
B. Law of Universal Gravitation

    This allows us to determine orbits

FG= G m1m2 / d2

mass vs. weight

moon 1/6 Earth