History of Astronomy

Early Astronomy

• Astronomy Is science that the universe • • Greeks 600 B.C. – A.D. 150 Measured distances to the Sun and Moon

Eratosthenes

Eratosthenes  Successfully Measured the circumference of the Earth  1.7% Error 2400 Years Ago

Geocentric View

Geocentric View  Pre 300 B.C.

 Earth is the center of the Univerese  The orbs (Sun, Moon, Mercury, Venus, Mars and Jupiter) orbit the Earth each day  Surrounded by a Hollow Sphere

Heliocentric

• • Aristarchus (312-230 B.C.) Earth and the other planets orbit the sun Dominated Western Thought for over 2000 Years

Ptolemaic System

• • • Ptolemy (A.D. 141) Believed in Geocentric Model Observed Retrograde Motion – Planets Move to the East, but periodically they stop and reverse direction Social Bias in Science

Modern Astronomy

• • Renaissance of Science Broke Away from Religious and Philosophical Views Used Natural Laws to explain the motions of the Heavens

Modern Astronomy

• • • • Nicolas Copernicus 1473-1543 Earth is a Planet Sun Centered Planets Orbited the Sun in Complete Circles

Modern Astronomy

• • Tycho Brahe 1546 -1601 Spent 20 yrs. Measuring the Locations of the Heavenly Bodies • • • • Johannes Kepler 1571-1630 Assistant to Brahe Discovered 3 Laws of Planetary Motion – Ellipse Determined the Distance from the Sun to Earth is 1AU = 150 Million km

Modern Astronomy

• • • • Galileo Galilei 1564 – 1642 Major Contribution was the behavior of the Moving Objects Ground Lenses to make telescopes Made Discoveries that supported Heliocentric View • • • • Sir Isaac Newton 1642-1727 Expanded on Galileo Force Formulated and tested the Law of Universal Gravitation at the age of 23 This is the force that makes planets revolve in a circle