History of Astronomy

The History of Astronomy

We expand our knowledge by adding to what people before us discovered.

Ptolemy A.D. 140

Reasoned that the Earth was the center of the universe.

People believed his “geocentric” system for more than 1500 years.

• Why: Because visually, it appeared to be correct.

His evidence:

• The moon circled the earth.

• The sun seemed to circle the Earth.

• He concluded that the stars must also.

His problem:

• Planet motions would not fit.

• This idea is called GEOCENTRIC

Ptolemy’s Model of the Solar System

• Ptolemy’s theory is known as the Geocentric Model because he thought the Earth was the center of the universe.

• In Greek, “Geo”

  means Earth

He believed his theory for several reasons

• Gravity of all objects were attracted to the earth, which suggested to him that the earth must be the center.

• He thought the Earth did not move because objects fell in the same place if thrown up in the air.

Ptolemy's Model: Notice where the sun is!

Multiple Choice

Ptolemy reasoned that the _________ was the center of the universe.

• Earth

• Sun

• Moon

Multiple Choice

Ptolemy's model of the Solar System was called the _________ theory.

• Geocentric

• Correct

• Earth-king

• Suncentric

Multiple Choice

In Greek, "GEO" means...

• Moon

• Earth

• Sun

• Planets

Early astronomers looked for patterns and mathematical relationships.

Astronomers wanted to find evidence to support or reject Ptolemy’s ideas.

Nicholas Copernicus

• Polish Astronomer & Mathematician

• Early 1500's

Nicholas

Copernicus

Copernicus’s Model of the Solar System

• Copernicus’ theory is called the Heliocentric Theory because he thought the sun was the center of the universe.

• In Greek, “helios” means sun

Copernicus’s Model of the Solar System

• Galileo made additional observations using a telescope, which supported the heliocentric theory.

• Galileo observed that Venus went through a full cycle of phase’s like the Moon. This could only be explained if Venus were orbiting the Sun.

Copernicus waited until just before he died to publish his work!

Why? Because he knew how upset many people would be about what he said.

Multiple Choice

Copernicus found evidence that the ________ revolved around the __________.

• Earth revolved around the Sun

• Moon revolved around the Sun

• Sun revolved around the Moon

Multiple Choice

This is known as the _____________ Theory.

• Geocentric

• Suncentric

• Heliocentric

• Lunarcentric

Multiple Choice

Copernicus also found that the Earth rotated to cause _______.

• night & day

• a month

• a year

Multiple Choice

Another discovery of Copernicus' was that the Earth revolved around the Sun to cause ___________.

• a month

• a day

• a year

• a night

Multiple Choice

Which Astronomer made additional observations which supported the Heliocentric Theory?

• Ptolemy

• Galileo

Tycho Brahe

1546 - 1601

Tycho Brahe collected quantitative data for many years.  

• Often he did not see the relationships among his data, but kept it anyway.

Tycho Brahe

• First to predict that orbits were not circular.

• Measured length of day to within 1 second.

• Data was later used to prove that the planets orbit the sun.

Johannes Kepler

1571 - 1630

Johannes Kepler

• Kepler was an assistant to Tycho Brahe in the late 1500s.

• He took Tycho’s years of observations and used math to come up with his laws of planetary motion.

Johannes Kepler

• He figured out that planets closer to the sun feel a stronger solar force and therefore have to move faster to overcome the sun’s gravity.

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• He used Tycho’s data to figure out that the planets’ orbits are not round, but are ellipses.

Galileo Galilei

1564 - 1642

Galileo Galilei

Galileo Galilei

View through a telescope showing rotating moons of Jupiter.

Photo of Venus going through phases like the moon.

Picture of Galileo’s original drawings of Saturn and Venus.

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Galileo's

telescope

And then came -

Sir Isaac Newton

Sir Isaac Newton

• He determined that the balance between inertia and gravity keeps planets in orbit.

Inertia  - - - -

The tendency of a moving object to continue in a straight line -

or a stationary object to remain at rest.

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Gravity - - - -

The attractive force between objects -

the force depends on the mass  of the two objects.

Newton's telescope

Newton invented a new telescope using mirrors.

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Multiple Choice

Johannes Kepler was an assistant to ____

• Galileo Galilei

• Tycho Brahe

• Sir Isaac Newton

• Copernicus

Multiple Choice

Which planet did Galileo discover had phases like the moon?

• Mercury

• Venus

• Earth

• Jupiter

Multiple Choice

The tendency of a moving object to continue in a straight line - or a stationary object to remain at rest.

• Gravity

• Inertia

Multiple Choice

The attractive force between objects - the force depends on the mass of the two objects.

• Gravity

• Inertia