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22.1 Early Astronomy
The Birth of Modern Astronomy
 Nicolaus Copernicus
• a Polish Astronomer
Copernicus concluded that Earth is a planet
He theorized that the Sun was at the center of
the Universe, and that the Earth and other
planets revolved around it.
STILL WRONG
The Copernican Model of the
Universe It did 3 things
• It explained the motions of the planets.
• It took the Earth out of it’s spot as the
center of the universe.
• it expanded the size of the Universe.
22.1 Early Astronomy
The Birth of Modern Astronomy
 Tycho Brahe
• Tycho Brahe designed and built instruments to
measure the locations of the heavenly bodies.
did not accept Copernicus’ model of the universe.
He attempted to combine it with the Ptolemaic model. He
proposed that the five known planets revolved around the sun,
which, along with those planets, revolved around the earth each
year.
The stars, then, revolved around the Earth, which was
immobile.
Tycho Brahe’s first contributions to astronomy was the
detection and correction of several errors in the standard
astronomical tables.
22.1 Early Astronomy
The Birth of Modern Astronomy
 Johannes Kepler
• Kepler discovered three laws of planetary motion:
1. Orbits of the planets are elliptical.
2. Planets revolve around the sun at varying
speed.
3. There is a proportional relationship between
a planet’s orbital period and its distance to
the sun.
22.1 Early Astronomy
The Birth of Modern Astronomy
 Johannes Kepler
• 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.
Planet Revolution
22.1 Early Astronomy
The Birth of Modern Astronomy
 Galileo Galilei
• Galileo’s most important contributions were his
descriptions of the behavior of moving objects.
• He developed his own telescope and made
important discoveries:
1. Four satellites, or moons, orbit Jupiter.
2. Planets are circular disks, not just points of light.
3. Venus has phases just like the moon.
4. The moon’s surface is not smooth.
5. The sun has sunspots, or dark regions.
The Solar System Model Evolves
22.1 Early Astronomy
The Birth of Modern Astronomy
 Sir Isaac Newton
• Although others had theorized the existence of
gravitational force, Newton was the first to
formulate and test the law of universal
gravitation.
 Universal Gravitation
•There is a gravitational force acting between any two
objects in the universe.
Gravitational force decreases with distance.
• The greater the mass of an object, the greater is
its gravitational force.
• We don't fall towards the people next to us
because they are much less massive than
Earth. But the Sun is more massive than
Earth. Why don't we fall to the Sun?
• It is much farther away. As the distance
between two objects gets larger, the
gravitational force between them gets
smaller.