1. Origin of Modern Astronomy
Chapter 22.1

2. Astronomy is the study of the universe
Ancient Greeks used philosophical arguments to explain natural events
Geocentric Model (Aristotle and Ptolemy)
Geo means “Earth”
Centric means “located in the center”
The moon, sun, and the known planets (Mercury, Venus, Mars, and Jupiter) orbit the Earth
Heliocentric Model (Aristarchus and Copernicus)
Helio means “Sun”
The Earth and the other planets orbit the sun
The Greeks also used some observational data

3. Geocentric and Heliocentric Models

4. The Birth of Modern Astronomy
Claudius Ptolemy created a model of the universe that accounted for the movement of the planets
Retrograde motion is the apparent westward motion of the planets with respect to the stars

5. Retrograde Motion

6. The Birth of Modern Astronomy
Nicolaus Copernicus concluded that Earth is a planet. He proposed a model of the solar system with the sun in the center.

7. The Birth of Modern Astronomy
Tycho Brahe designed and built instruments to measure the locations of the heavenly bodies. His observations, especially of Mars, were far more precise than any made previously.

8. The Birth of Modern Astronomy
Johannes Kepler discovered three laws of planetary motion:
Orbits of the planets are elliptical
Planets revolve around the sun at varying speed
There is a proportional relationship between a planet’s orbital period and its distance to the sun

9. Kepler Vocabulary An ellipse is an oval-shaped path
An astronomical unit (AU) is the average distance between Earth and the sun; it is about 150 million kilometers

10. Planet Revolution

11. The Birth of Modern Astronomy
Galileo Galilei’s most important contributions were his descriptions of the behavior of moving objects
He developed his own telescope and made important discoveries

12. Galileo’s important discoveries
Four moons orbit Jupiter
Planets are circular disks, not just points of light
Venus has phases just like the moon
The moon’s surface is not smooth
The sun has sunspots, or dark regions

13. The Birth of Modern Astronomy
Sir Isaac Newton was the first to formulate and test the law of universal gravitation
Gravitational force decreases with distance
The greater the mass of an object, the greater is its gravitational force