Origin of Modern Astronomy

Unit 7 Chapter 22

Chapter 22.1: Early Astronomy

Astronomy: the study of the universe, the properties of objects in space, and the laws under which the universe operates.

The “Golden Age” of modern astronomy was centered in Greece. (600B.C.E- A.D.150)

Developing the basics of geometry and trigonometry allowed them to measure the distances of the sun and the moon.

The astronomical discoveries that the Greeks made relied on careful observation

Aristotle, a famous Greek philosopher concluded the Earth was round based on the curved shadow it cast on the moon.

Eratosthenes, estimated the circumference of the Earth based on angles of the noon sun in two different cities

Hipparchus,Determined the location of 850 stars, developed the first measurement of a “year”, and developed a method for predicting lunar eclipses

The Greeks believed in a geocentric view of the universe.

In a geocentric model the moon, sun and the other planets orbit the Earth.

Stars were contained on a transparent hollow sphere called the celestial sphere

The seven “wanderers” included the sun, the moon, Mercury, Venus, Mars, Jupiter, and Saturn.

Aristarchus (312-230 BCE) proposed a heliocentric, or sun-centered, model of the solar system. Where the sun is in the center and the other planets orbit the Sun.

He used geometry to calculate the size of the sun and the moon and determined that the sun was much larger than the Earth.

In AD 141, Claudius Ptolemy published his work accounting for planetary movement within the universe which he called Ptolemaic system.

Ptolemy’s model was based off the geocentric model of the planets orbiting the Earth.However, he noticed that planet motion had a unique drift which he called retrograde motion.

Retrograde motion: apparent westward shift in motion in relation to the stars.

The Birth of Modern Astronomy

Nicolaus Copernicus (1473- 1543) concluded that Earth was a planet and that the sun was the center of the solar system.

Tycho Brahe (1546-1601) designed and built instruments to measure locations of planetary bodies.

Johannes Kepler (1571- 1630)trained by Brahe, Kepler discovered the three laws of planetary motion.

Planetary Laws of Motion