History of Astronomy

“Progress in science is often slow and intermittent and may require a great deal of patience before significant progress is made” (McMillan 18).

Aristotle Greek Philosopher B.C. Geocentric: Earth center of the universe Taught the perfect form: Circle Pros: Described the moon and sun’s orbit Cons: variations in planetary brightness and planets orbits phillwebb.net

Claudius Ptolemaeus Ptolemy 40 AD Ptolemaic model ◦ Described 5 planet orbits well Building off Aristotle's version and what observers had observed in the sky dealing with planetary motion reocities.com

Claudius Ptolemaeus ptolemy.berkeley.edu

Aristarchus of Samos Lived: B.C. All planets, including Earth, revolve around the sun. Earth rotates on its axis once each day Why his ideas weren’t accepted: Politics, Aristotle’s ideas won the popular vote

“Usually one generation of scientists can bring sufficient objectivity to bear on a problem, though some especially revolutionary concepts are so swamped by tradition, religion, and politics that more time is need” (McMillan 31).

Nicholas Copernicus Polish Cleric ◦ 16 th century Copernican Revolution ◦ All planets orbit the sun ◦ Explained planets orbits and variation in planetary brightness ◦ Wrote of his findings, but claimed them as only a mathematical hypothesis  Keep him out of trouble with the church ◦ Never excepted during his life time  Went against the religious view points at the time  Contradicted conventional wisdom: didn’t match Aristotle thinkers.

Nicholas Copernicus indiamart.com ml Diagram of the Copernican system, from De Revolutions

Galileo Galiei Italian mathematician and philosopher Used the brand-new technology to further humans understanding = telescope ◦ Telescope was invented in Holland in early 17 th century Performed experiments to test his ideas ◦ ‘Father of experimental science’ quotationsbook.com marcdatabase.com

Galileo’s Discoveries Moon has mountains, valleys, and craters Sun has imperfections-dark blemishes now known as sunspots Sun rotates approximately once per month around an axis roughly perpendicular (right angle) to the Earth’s orbit. Jupiter’s moon (4 of them) Venus show a complete cycle of phases, similar to the moon

Galileo’s Popularity His ideas were opposite to what science thought at that time 1610 published his findings agreeing with Copernican theory his ideas were judged contrary to accepted belief of that time Both his and Copernicus were banned by the ‘Church’ Told to abandon his astronomical pursuits ◦ Which he didn’t “These actions brought Galileo into direct conflict with the Church. The Inquisition forced him, under threat of torture, to retract his claim that Earth orbits the Sun, and he was placed under house arrest in 1633” (McMillan 30). ◦ It wasn’t until 1992, did the ‘Church’ publicly forgave Galileo ‘crimes’

Tycho Brahe , Denmark Studied astrology, alchemy, and medicine Kept meticulous records of stars, planets, and celestial events. He move to Prague, after a falling out with the Danish courts There he hired Kepler to find a theory that could explain Brahe’s planetary data ◦ Year later Brahe died and Kepler inherited Brahe potion (Imperial Mathematician of the Holy Roman Empire) and possession

Johannes Kepler 16 th century German mathematician and astronomer Took him 29 years to try and find an unifying principle to explain the motions of the planets ◦ Data was collected by Brahe libwebspace.library.cmu.edu

Kepler’s Laws I. The orbital paths of the planets are elliptical with the Sun at one focus ◦ Ellipse is a flattened circle, a circle is a special kind of ellipse II. An imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal intervals of time. ◦ When the planet is closer to the Sun it must move faster then it is further away ◦ This applies to any orbiting object III. The square of a planet’s orbital period is proportional to the cube of its semi-major axis astro.psu.edu hyperphysics.phy-astr.gsu.edu

Isaac Newton 17 th century British physicist/mathematician Newtonian Mechanics ◦ 3 basic laws of motion, the laws of universal gravitation, and a little calculus en.wikipedia.org

Newton’s 1 st Law Inertia: the tendency for an object to keep moving in the same direction and speed unless acted upon by an outside force. More mass = greater inertia and the more force is needed to change its motion

Newton’s 2 nd Law The acceleration of an object is directly proportional to the net applied force and inversely proportional to the object mass ◦ Greater force or smaller mass = increase acceleration ◦ F=ma

Newton’s 3 rd Law To every action there is an equal and opposite reaction

Laws of Universal Gravitation Gravitational force: things with mass exerts attraction on other masses “ The mutual gravitational attraction of the Sun and the planets, as expressed by Newton’s law of gravity, is responsible for the observed planetary orbits” (McMillan 37). ◦ The Sun pulls the planets changing the planets forward motion into a curved path

Newton’s revision to Kepler’s Laws I. The orbit of a planet around the Sun is an ellipse having the center of mass of the planet-Sun system at one focus ◦ The center of mass of two objects about the same size is outside either object. However if one object is larger then the other the center of mass shifts towards the larger object. III. Changed the math to use the combined mass of the two object, which made it more correct and also allowed it to be used outside our solar system