Periods of Western Astronomy Western astronomy divides into 4 periods Prehistoric (before 500 B.C.) Motions of Sun, Moon, & stars observed Keeping time and directions develops 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) 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, based on the belief that the sphere is the perfect shape used by the gods
Who? Early Ideas: Aristotle – 300 BC The Earth is round Shape of Earth’s shadow on the Moon during an eclipse A traveler moving south will see stars previously hidden by the southern horizon
Who? Early Ideas: Aristarchus – 280 BC Found relative dimensions of the solar system Earth was much smaller than the distances to the celestial bodies Heliocentric (Sun-centered) model for the solar system
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? Eudoxus (400-347 B.C.) Proposed a geocentric model in where each celestial object was mounted on its own revolving transparent sphere with its own separate tilt
Who? Ptolemy of Alexandria (140 AD) Improved the geocentric model by stating that each planet moved on a small circle, which in turn had its center move on a much larger circle centered on the Earth The small circles were called epicycles and this tried to explain retrograde motion
Who? Nicolas Copernicus (1473-1543) Re-examined the heliocentric model and used it to explain retrograde motion Data did not make sense with geocentric model Heliocentric models explain retrograde motion as a natural consequence of two planets (one being the Earth) passing each other
Who? Nicolaus Copernicus (1473-1543) Found relative distances of the planets from the Sun However, problems remained: Could not predict planet positions any more accurately than the model of Ptolemy
Who? Tycho Brahe (1546-1601) Made meticulous measurements & observations of the planets, supernovas, & comets Proposed a compromised geocentric model Designed & built instruments of far greater accuracy than any yet devised
Who? Johannes Kepler (1571-1630) Using Brahe’s data, discovered that planets move in ellipses with the Sun located at one of the two foci (not in circles)! He also created something we will learn about more later called Kepler’s Three Laws!
Who? Galileo (1564-1642) Used the telescope to study the heavens & noticed: The Moon is made of rock with a surface similar to Earth’s The Sun has spots. changes its appearance, & rotates Jupiter has four objects (moons) orbiting it Milky way is filled with many stars
Who? Isaac Newton (1642-1727) - born the year Galileo died – CREEPY? Major advances in mathematics, physics, and astronomy “Discovered” gravity & calculus