Periods of Western Astronomy Western astronomy divides into 4 periods Prehistoric (before 500 B.C.) Cyclical motions of Sun, Moon and stars observed Time and directions develop Classical (500 B.C. to A.D. 1400) Measurements of the heavens Geometry and models to explain motions
Periods of Western Astronomy Renaissance (1400 to 1650) Accumulation of data led to better models Technology (the telescope) enters picture Modern (1650 to present) Physical laws and mathematical techniques Technological advances accelerate
Who? Early Ideas: Pythagoras (500 BC) Earth was round Evidence: the sphere is the perfect shape used by the gods
Who? Early Ideas: Aristotle (300 BC) Earth is round: Evidence: Shape of Earth’s shadow on the Moon during an eclipse Evidence: Traveler moving south will see stars previously hidden by the southern horizon
Who? Eratosthenes (276-195 B.C.) made the first measurement of the Earth’s size He obtained a value of 25,000 miles for the circumference, a value very close to today’s value
Who? Ptolemy of Alexandria (140 AD) Geocentric model (earth- centered) Assumed: Each planet moved on a small circle, which in turn had its center move on a much larger circle centered on the Earth (epicycles) – explained retrograde motion http://www.youtube.com/watch?v=72FrZz_zJFU
Who? Nicolaus Copernicus (1473-1543) Heliocentric (sun-centered) models explain retrograde motion as a natural consequence of two planets (one being the Earth) passing each other Relative distances of the planets from the Sun BUT could not predict planet motion
Who? Tycho Brahe (1546-1601) Made observations of a supernova and comets - the heavens were both changeable and more complex than previously believed Designed and built more precise & accurate instruments Made measurements of the planets – gathered data
Who? Johannes Kepler (1571-1630) Tycho’s data passed to Kepler, his young assistant Kepler derived his three laws One: Using Mars data, Kepler showed the orbit of planets to be an ellipse with the Sun at one foci Two: Planets will sweep out in equal distances in equal times Three: The farther the semi-major axis, the longer the orbit (a3=p2)
Who? Galileo (1564-1642) – house arrest! Invent and use the telescope to observe space Found: The Moon’s surface has craters and is made of rock The Sun has spots, changes its appearance, and rotates Jupiter has four moons orbiting it Milky Ways has many stars
Who? Isaac Newton (1642-1727) - born the year Galileo died - CREEPY Major advances in math (calculus), physics (motion/optics), and astronomy(gravity) Newton’s laws of motion and gravity