Introduction to Astronomy And let there be light! Introduction to Astronomy

The Beginnings of Astronomy I The Universe – Everything there is; all of Creation; all energy, space, and matter Astronomy – The study of the universe beyond the earth’s atmosphere System – that thing you’re observing Solar System – the system comprised of the Sun and those objects the Sun holds by its gravitational force. The Solar System is composed of: A medium-sized yellow star (The Sun), 9 planets, over 60 satellites (moons) orbiting the planets, thousands of asteroids, countless meteoroids and comets, the solar wind (plasma) gases, and interplanetary dust.

All ancient civilizations wanted to learn about astronomy for religious purposes—when to plant, harvest, when to offer sacrifice. Stonehenge outside of Salisbury, England, is an example of a stone age observatory, but 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, as the scientific method was forged and refined in the crucible of Western Europe and the controversies involved in heavenly motions. The people who made things happen:

Beginnings of Astronomy III Models of the Solar System Aristotle, Hellenistic astronomy, and the Medieval Church – Geocentric View Copernicus – Heliocentric model, circular orbits Brahe – Magnificent experimentalist whose meticulous observations and measurements of planetary motion set the stage for the refinement of the Copernican Model. Kepler – The measured period of Mars’ orbit was 8 minutes/yr different from predictions based on Copernican model. Showed inadequacy of circular orbits. Used elliptical orbits to eliminate error. Newton - His law of Universal Gravitation gave a model explaining why planets revolved around the Sun.

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Ptolemy 90-168 AD Adopted around 460 AD by western religions. Ptolemy’s model stood unchallenged for 1400 years. And because its proposition that Earth was the center of the universe dovetailed so nicely with the Church’s teaching that Earth and its inhabitants were the center of God’s creation, the two became inextricably intertwined. The Church endorsed Ptolemy’s model precisely because it fit biblical accounts of the creation of the universe by God. The geocentric system had by then become an article of faith, closed to any scientific scrutiny.

That Ptolemy could place Earth at the center of the universe and still predict the planets’ positions adequately was a testament to his ability as a mathematician. That he could do so while maintaining the Greek belief that the heavens were perfect—and thus that each planet moved along a circular orbit at a constant speed—is nothing short of remarkable.

Ptolemy on Orbits 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 travelled along a larger circle, called a deferent, with Earth at its center.

Introduce the ellispe 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.)

And second, he had the center of the epicycle move at a constant angular speed around a third point, called the equant, which lay on the opposite side of the deferent’s center from Earth. These modifications allowed Ptolemy to predict the positions of the planets with reasonable—though far from perfect—accuracy.

1/18 > sin 3 > 1/20 Distance between sun and moon Historians of mathematics have, as a rule, given too little attention to Aristarchus of Samos. The reason is no doubt that he was an astronomer, and therefore it might be supposed that his work would have no sufficient interest for the mathematician. The Greeks knew better; they called him 'Aristarchus the mathematician'.

Copernicus- 1473 -1543 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. Although the Greek astronomer Aristarchus developed the same hypothesis more than 1500 years earlier, Copernicus was the first person to argue its merits in modern times. The Sun was Copernicus’ center of the universe, encircled by Mercury, Venus, Earth, Mars, Jupiter, and Saturn.

Tycho Brahe – 1546 -1601 was a Danish nobleman known for his accurate and comprehensive 25 years.) astronomical and planetary observations. 1546-1601

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, based on his works 

Keplar – 1571 1630 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" that geometers call ellipses

Laws of Planetary Motion The Orbits of Planets are ellipses, with the sun at one focus of the ellipse. The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse. The ratio of the square of the revolutionary periods for two planets is equal to the ratio of the cubes of the Semi-major axis. he orbits of the planets are ellipses, with the Sun at one focus of the ellipse. The orbits of the planets are ellipses, with the Sun at one focus of the ellipse.

Galileo Galilei – 1564 - 1642 1564-1642 Pisa Italy  was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the scientific revolution.

A true scientist Galileo developed an arrogance about his work, and his strident criticisms of Aristotle left him isolated among his colleagues. Galileo refined his theories on motion and falling objects, and developed the universal law of acceleration, which all objects in the universe obeyed.

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

Inventions and improvements Telescopes Thermometer Gravity? Tower of Piza Magnets Regulated clocks

Sir Isaac Newton – 1642 - 1727 England Light based on Keplar De Mathimatica – Pricipa…Calculus. Involving bodies in motion – planets. Gravity from Keplar and Hooke

Isaac Newton Eccentric/ Brilliant / Head of Royal Academy of science in latter years. Mathematics Astronomy Light and Color Motion – Physics – law of motion. Theology