Planets & The Origin of Science Reading: Chapter 2 Required: Guided Discovery (p.44-47) Required: Astro. Toolbox 2-1 Optional: Astro. Toolbox 2-2, 2-3 Next Homework Due. Sept. 26 Office Hours: Monday, Tues. 3-4
Planets: Wanderers in The Sky! Ancient peoples noticed that five stars seemed to move...! They called them Planets which means wanderers.! Every ancient culture was aware of these 5 planets.! Words for the days of the week derive from the 5 visible planets: Mercury, Venus, Mars, Jupiter, and Saturn.
How Planets Move! In one night, the planets move from East to West due to Earth s rotation.! But, Night after night, planets drift slowly from West to East with respect to the background stars.! This is called direct motion.! However sometimes a planet reverses direction!! We call this backward drift retrograde motion. ast West
Ptolemy s Geocentric Model! Greek scientist Ptolemy worked at the Great Library of Alexandria in Egypt (~140 AD)! His research included astronomy, astrology, geography & music.! Ptolemy used a geocentric model of the solar system explain retrograde motion.! Earth was at the center.! In Ptolemy s model, the planets travel along small circles (epicycles) that move on larger circles.
Ptolemy s Geocentric model
Geocentric Model Planets Circle the Earth on epicycles anim.
The Geocentric Model! Ptolemy s views were published in a book: the Almagest! Because it could explain retrograde motion, his theory was widely accepted by European & Middle Eastern astronomers.! When later observations did not agree with the Geocentric Model, many small changes were added.! The Model became quite cumbersome, but it was widely accepted for 1,600 years!
How do you Challenge an accepted theory?! Arab scientist Alhazan* (965-1040) came up with a way.! Like Ptolemy, he lived in Egypt and studied many subjects (optics, astronomy, math, geometry)! A hypothesis must be proved by experiments that can be confirmed, he said.! Later scientists in Europe read his books, and developed what we now call the scientific method. *a.k.a. Ibn al-haytham
Copernicus Heliocentric theory! We credit Nicolaus Copernicus, a 16th-century Polish astronomer, with our modern view of the Solar System! Copernicus suggested a heliocentric theory! Sun was at the center of the Solar System.! Planets moved in circles around the Sun. Copernicus could also explain retrograde motion.
I began to be annoyed that the movements of the world machine were not understood with greater certainty by the philosophers, who otherwise examined so precisely the most insignificant trifles of the world. Copernicus, Book on the Revolutions, 1543
it is just like someone taking from various places hands, feet, a head, and other pieces, each very well depicted, but not for the representation of a single person. In forcing these fragments together, they created a monster rather than a man. Copernicus, Book on the Revolutions, 1543
An inner planet (eg. Earth) catches up with an outer planet (eg. Mars) causing it to appear to move backward (retrograde motion)
Copernicus Heliocentric Theory! Copernicus new theory clearly stated planets positions relative to the Sun! It predicted the next appearances of planets in the sky.! These predictions proved correct, lending support to Copernicus Heliocentric Model.! However, his model was no more accurate than the Geocentric model
A Heretical Idea?! Copernicus Heliocentric theory caused problems with the Church.! The Church had accepted Ptolemy s geocentric universe.! It agreed with the Church s notion of heaven as a perfect place.! To question this model was to question the Church s authority.! Copernicus book was censored by the Catholic Church.! Copernicus died before the full effects of his model were felt! However, other astronomers supported his model, using their observations.
Galileo Galileo Galilei (1564-1642) was an Italian scientist who studied many fields. He tried to measure the speed of light, and studied gravity. He obtained the first observations to confirm the Heliocentric Model
More Evidence for the Copernican Model! Galileo was the first person to use a telescope for astronomy.! Several of his observations supported the Heliocentric model of Copernicus:! He discovered moons orbiting Jupiter (not the Earth)
Galileo Galilei! Galileo observed Venus with his telescope.! He reported seeing crescent and gibbous phases on Venus! Gibbous phases are only possible if Venus is on the other side of the Sun from us.! This can t happen in the Geocentric model of the Universe!
Geocentric model Of Ptolemy
Theory: Venus is always between the Sun and Earth Prediction: Venus will always be seen in crescent phase http://astro.unl.edu/classaction/animations/renaissance/ptolemaic.html
Not to scale! Theory: Venus sometimes goes behind the Sun Prediction: Venus will sometimes be seen in gibbous phase. Telescope Observation: Venus does show gibbous phase! http://astro.unl.edu/classaction/animations/renaissance/venusphases.html