Chapter 19

I. Earth history of astronomy

A.Ancient Greeks

1.Use 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)

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 the sky

2.The seven wanderers included the

a.Sun

b.Moon

c.Mercury through Saturn

4.Aristarchus (312-230 B.C) was the first Greek to profess a sun-centered or heliocentric, universe

5. Planets exhibit an apparent westward drift

a.Called retrograde motion

b.Occurs as Earth with its faster orbital speed overtakes another planet

6.Ptolemaic system

a. A.D 141

b.Geocentric model

c.To explain retrograde motion, Ptolmy used two motions for the planets

1.Large orbital circles called deferents and

2.Small circles call epicycles

B. Birth of modern astronomy

1.1500s and 1600s

2.five noted scientists

a.Nicolaus Copernicus

1. Concluded Earth was 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.Ushered out old astronomy

b.Tycho Brahe

1.Precise observer

2.Tried to find stellar parallax

3.Did not believe in the Copernican system because he was unable to observe stellar parallax

c.Johannes Kepler

1.Ushered in new astronomy

2.Planets revolve around the sun

3.Three laws of planetary motion

a.Orbits of planets are elliptical

b.Planets revolve around the sun at varying speed

c.There is a proportional relation between a planet's orbital period and its distance to the sun (Aus) one AU averages about 150 million kilometers or 93 million miles.

d. Galileo Galilei

1. Supported copernican theory

2. Used experimental data

3.Constructed an astronomical telescope in 1609

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

5.Tried and convicted by the Inquisition

e.Sir Isaac Newton

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

II.Constellations

A.Configurations of stars named in honor of mythological characters or great heros

B.Today 88 constellations are recognized

C.Constellations divide the sky into units, like state boundaries

D.The brightness stars in a constellation are identified in order of their brightness by the letter of the Greek Alphabet

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