Chapter 22 Section 1 Early Astronomers Aristotle Copernicus Kepler GalileiNewton

Let’s start at the beginning… Ancient Greece – Golden Age (600 b.c. – a.d 150) – Relied on observations – Used geometry and trigonometry principles to measure size and distances of sun & moon. Aristotle – Earth is round—thought so b/c of Earth’s curved shadow on Moon – Theory abandoned in Middle Ages Eratosthenes – 1 st successful attempt to establish size of Earth – Used geometry to determine circumference of Earth (angles of Sun) Hipparchus – Star catalog—location of ~850 stars organizes according to brightness – Measured length of year to within minutes of modern year (current)

Earth is #1 ! Geocentric meaning Earth Centered was created by Claudiaus Ptolemy. He thought the earth was the center of everything in our Solar system. Oh wait… Sun is #1 ! Heliocentric meaning Sun Centered was created by Nick Copernicus and he thought and proved that the sun was the center of our solar system and every thing revolves around the sun.

Ptolemaic System Cladius Ptolemy – Ptolemaic system Accounted for the movements of the planets Retrograde motion – Apparent movement of a planet that appears to approach, reverse, and then continue onward – Occurs because Earth has a faster orbital speed than Mars (see below)

Modern Men Copernicus ( ) Poland – Earth as a planet, proved Earth rotates – Heliocentric theory Brahe ( ) Denmark – Designed and built angle-measuring device – Mars observations executed precisely

Modern Men: Kepler Danish; Brahe’s assistant 3 laws of planetary motion 1.Planet’s orbit is an ellipse (oval) shape with one focus. 2.The planet’s move faster when nearer the sun and slower when farther away (equal areas in equal time). 3.Square of length of time it takes a planet to orbit the sun (orbital period) is proportional to the cube of its mean distance to the sun (p 2 =a 3 ). Defined the term astronomical unit (Au) – Average distance between Earth & sun (~150 million km)

Modern Men: Galileo Italian Telescopes for more precise observations – 4 satellites (moons) orbiting Jupiter & other moving objects – Planets are circular disks; not just points of light. – Venus has phases just like the moon. – Rough, mountainous texture on moon. – Sunspots on Sun’s surface revealed rotational period of ~ 1 month

Modern Men: Newton English Formulated law of universal gravitation – All objects have gravity between them. – The greater the mass of the object, the greater the gravitational force. Laws of inertia and gravity – Without gravity, planets would move in a straight line out into space.

Contemporary Fellows Edwin HubbleHubble – American – Universe is still expanding – Galaxies outside of our own Stephen Hawking – 1942-_____ British – Theorized existence of black holes Carl Sagan – American – SETI, questioned Drake equation, popularized science and the Cosmos TV program James Webb Space TelescopeTelescope – Named after NASA administrator – Infared – Big bang theory and origin of universe