TOPIC #1:Chapter 22Origin of Modern Astronomy

Section 1: Early Astronomy• Astronomy is the science that studies the universe.

• The “Golden Age” of early astronomy was centered in Greece.

• Ancient Greeks like Aristotle studied the motion of heavenly bodies by observing and recording the motions.

Section 1: Early Astronomy• Early models of the solar system developed by the Greeks

were geocentric models these models were Earth centered.

• This means that the sun, moon and other planets orbit the Earth.

• Orbit- The path of an object as it goes around anotehr object in space

Section 1: Early Astronomy

Section 1: Early Astronomy• Some ancient Greeks believed in the heliocentric theory this

was the idea that the Earth, moon and other planets orbit the sun.

• There was no way of measuring or collecting data that could support either theory during the times of the ancient Greeks?

Section 1: Early Astronomy

Heliocentric Theory

Section 1: Early Astronomy• Claudius Ptolmey (A.D. 141) defended the geocentric theory of

the universe (which was later proven wrong).

• He believed that the motion of the planets across the nights sky was evidence of the geocentric theory.

• He even accounted for retrograde motion, which is the apparent westward motion of planets against the stars.

• The stars seem to move in an easterly direction but at times the planets seem to move in the opposite direction.

Section 1: Early Astronomy• Retrograde motion

did not help the geocentric theory but it defined the motion of planets “backwards”.

• It was later found that this was due to their own rotations on an axis.

Section 1: Early Astronomy• Polish astronomer, Nicolaus Copernicus (1473-1543) is

credited with discovering the heliocentric model of the solar system because he was able to support his discovery with data and evidence.

Section 1: Early Astronomy• Danish astronomer, Tycho Brahe (1546-1601) advanced the

study by inventing many tools used to observe and measure planetary motion.

• He had an assistant named Johannes Kepler (1571-1630) who furthered his study.

• Kepler is credited with discovering the Three Laws of Planetary Motion.

• These laws identify and define how planetary bodies orbit the sun and each other.

Section 1: Early Astronomy• Kepler defined the shape of the path planetary bodies orbit in

as an ellipse.

• From these laws of motion we have developed a way of measuring distance in space.

• The distance between the Earth and the sun is called an astronaumical unit (AU).

• This is used as the system of measurement when talking about any distance in space.

Section 1: Early Astronomy• Galileo Galilei (1564-1642), an Italian astronomer was the first

person to use the telescope to study space.

• He made many discoveries that supported Copernicus’s heliocentric model of the universe.

Section 1: Early Astronomy• Sir Issac Newton (1642-1727) was a British astronomer who

made arguably the most important discovery in all of astronomy.

• He is credited with defining and proving the existence of gravity.

• Gravity is the attractive force all objects have which determines the motion of objects in space.