The Origin of Modern Astronomy Chapter 4 The Origin of Modern Astronomy

4-1 The Roots of Astronomy The study of astronomy of ancient people is known as ________________ The Best known example of archaeoastronomy is Stonehenge built form 3000 BC to 1800 BC Most of what may have been discovered by early ancient peoples has been lost

4.1 The Roots of Astronomy The Astronomy of Greece Heavily influenced by religion and astrology. 624-547 BC- Thales of Miletus- a Greek philosopher taught that the universe is rational and the human mind can understand why the universe works the way it does. 570-500 BC- Pythagoras- a Greek philosopher- connected things in nature with mathematics

4.1 The Roots of Astronomy 428-347 BC – Plato- not an astronomer, taught the most perfect geometric form was a sphere and therefore the perfect havens must be made up of spheres- this influenced astronomers and the principle of uniform circular motion

4-1 The Roots of Astronomy 384-322 BC- Aristotle- one of Plato’s students- involved in many subjects. Believed that the universe was divided into two parts- Earth, corrupt and changeable and the heavens, perfect and unchanging. He believed that Earth was the center of the universe and called his model a geocentric universe. A century later Aristarchus proposed a theory that Earth rotated on its axis and revolved around the sun. Most of what he wrote is lost.

4-1 The Roots of Astronomy

4-1 The Roots of Astronomy 200 BC Eratosthenes- found a way to calculate Earth’s radius Hipparchus- usually credited with the invention of trigonometry, compiled the first star catalog and discovered precession.

4-1 The Roots of Astronomy 140 AD- Ptolemaeus- studied the motion of the planets

4-2 The Copernican Revolution 1473- AD Copernicus- Controversial idea of a heliocentric universe 1514- put his idea into a pamphlet to be published but was afraid to publish it at the time 1540- lets a friend publish his pamphlet

4-2 The Copernican revolution Galileo- according to our text he did not invent the telescope and not condemned by the Inquisition for believing that Earth moved around the Sun Even though Galileo didn’t invent the telescope, he was one of the first people to observe the sky with a telescope Observed sun spots on the sun and Venus had phases like the moon READ and SUMMARIZE the trail of Galileo

4-3 The puzzle of the planetary motion 1546 AD Tycho Brahe- observational astronomer Interesting Fact: In college he was in a duel… he ended up with a wound that disfigured his nose and for the rest of his life wore a false nose of gold and silver While he made observations- he noticed that Jupiter and Saturn passed very close to one another at a time that was not indicated in previous tables, showing errors. 1572 a “new star” appeared in the sky- Tycho’s supernova. According to Aristotle the starry sphere (furthest from Earth) was perfect and unchanging

4-3 The puzzle of the planetary motion 1573- Tycho announced his discovery that the new star did not show parallax so would have to reside in the starry sphere in a small book De Stella Nova (The new star) Friends with a Danish King- Frederik II, who gave Tycho money to build an observatory He could not measure parallax for the stars and concluded that Earth had to be stationary, so he rejected the Copernican Hypothesis He did not have telescopes they were invented a century later- he used large instruments to measure angles.

4-3 The puzzle of planetary motion

4-3 the puzzle of planetary motion Kepler Believed in the Copernican Theory 1600 hired by Tycho who died a year later Studied mars to see/learn how planets moved 1606 realized that the planets moved on an ellipse and not a circle Planets move faster when closer to the sun and slower when farther away His new discoveries helped prove against circular and uniform motion.

4-3 The puzzle of planetary motion Kepler’s 1st law: the orbits of the planets around the sun are ellipses with the sun at one focus Ellipse semimajor axis, a= half of the longest diameter eccentricity, e= distance from either focus to the center of the ellipse/the semimajor axis Circle is an ellipse with eccentricity equal to zero

4-3 The puzzle of planetary motion Kepler’s 2nd law: A line from a planet to the sun sweeps over equal areas in equal intervals of time Kepler’s 3rd law: A planet’s orbital period is proportional to its average distance from the sun cubed: