Add to table of Contents: Planetary MotionPg. 72 Early AstronomersPg. 73

Background: don’t write The Universe – Everything there is; all energy, space, and matter Astronomy – The study of the universe beyond the earth’s atmosphere. Solar System – the Sun and all the objects that travel around it due to gravitational force. Objects = planets, over 60 satellites (moons) orbiting the planets, thousands of asteroids, countless meteoroids and comets, and interplanetary dust.

Asteroid = large rock 1000km to 10m

Meteoroids = rocks less that 10 meters

Meteor = a meteoroid that is flaming hot from entering Earth’s atmosphere. Meteorite= meteor that survives atmospheric entry and lands on earth.

Comets = dust, ice, and gases (dirty snowball)

Ancient civilizations wanted to learn about astronomy for religious and societal purposes— when to plant crops, harvest them, when to offer sacrifice, etc. Mesoamerican tribes, the Anasazi, the Babylonians, and other ancient civilizations also developed calendars based on relatively sophisticated astronomical observations. The history of science involves the history of astronomy and the controversies involved in heavenly motions.

Aristotle B.C. Greek Philosopher 1 st to suggest the Earth- centered solar system model (Geocentric). Couldn’t explain why sometimes planets appeared to move backward, relative to other planets.

Ptolemy AD Greek Astronomer Created the earth centered model of the solar system = geo-centric. Ptolemy’s model stood unchallenged for 1400 years. This was due to the fact that it proposed that Earth was the center of the universe and this matched with the Church’s teaching that Earth and its inhabitants were the center the universe. The geocentric(=earth-centered) system then become an article of faith, closed to any scientific scrutiny.

Ptolemy explained planet orbits and rotations. The greatest difficulties he had to overcome were explaining the changing speeds and the occasional east-to-west, or retrograde, motion of the planets. He accomplished this by having each planet move along a small circle, called an epicycle, whose center traveled along a larger circle, called a deferent, with Earth at its center.

Introduced the ellipse Although this scheme came close to accomplishing what he wanted, it still came up a little short. So Ptolemy made a couple of refinements. First, he placed Earth slightly away from the center of the deferent. (A slightly off-center circle comes very close to mimicking an ellipse.)

Copernicus As a Polish astronomer, Copernicus made a great leap forward by realizing that the motions of the planets could be explained by placing the Sun at the center of the universe instead of Earth. In his view, Earth was simply one of many planets orbiting the Sun, and the daily motion of the stars and planets were just a reflection of Earth spinning on its axis. Created the sun-centered model of the solar system = Heliocentric.

Tycho Brahe – Brahe was a Danish nobleman known for: accurate and comprehensive observations of the solar system. He observed a bright “new star” and named it a supernova.

Johannes Kepler A German mathematician, astronomer, and astrologer. A key figure in the 17th century scientific revolution, he is best known for his: laws of planetary motion

Keplar – Kepler believed firmly in the Copernican system. Kepler was forced finally to the realization that the orbits of the planets were not the circles demanded by Aristotle and assumed implicitly by Copernicus, but were instead the "flattened circles”. Determined planets did rotate in elliptical paths.

Galileo Galilei – Pisa Italy was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the scientific revolution.

A true scientist Galileo refined his theories on motion and falling objects, and developed the universal law of acceleration, which all objects in the universe obeyed.

Inventions and improvements: Refracting(light bending) Telescope Galileo Thermometer Gravity experiment at the Tower of Piza Designed mechanism for pendulum clocks

Soon Galileo began mounting a body of evidence that supported Copernican theory and contradicted Aristotle and Church doctrine. There were Mountains on the moon. Jupiter was orbited by four moons. The sun had spots Venus had phases.

Sir Isaac Newton – English scientist

Contributions of Isaac Newton Created calculus Astronomy – built first practical reflecting telescope. 3 Laws of Motion Studied Light and Color Universal laws of gravitation – gravity held planets in orbit

Planetary Motion Pg. 72 Draw Models! Geo-Centric

Helio-Centric