A Brief History of Astronomy Ancient Astronomy Geocentric

A Brief History of Astronomy Ancient Astronomy Geocentric Universe Socrates, Aristotle & Ptolemy Heliocentric Universe Copernicus, Galileo, Tycho & Kepler The New Science of Newton Modern Astronomy

Ancient Egypt (3000 BC - 2000 BCE) 365 day calendar 12 months of 30 days 3 10 -day weeks with 5 day intercalation period at end of year (like leap year) Step Pyramid built by King Zoser (2800 BC) • Faces north • east entrance (sunrise) • west exit (sunset) Year began with Nile inundation and appearance of Sirius (July)

Ancient Greece Philosophy of Nature (Science)_ Nature should be looked at as it worked on its own, so by conducting an experiment, nature was put in "unnatural" circumstances, and hence the results of an experiment would not agree with the true way nature worked.

Pythagoras (582 -500 BCE) Founded school of mathematics and philosophy The Pythagorean Paradigm had three key points about the movements of celestial objects: 1. Their motion is perfectly circular 2. The Earth is at the exact center of their motion 3. Their motion is perfectly uniform

Plato (Student of Socrates) 427 -347 BCE There absolute truths obtainable through mathematics. (From the Pythagorean Doctrine) Plato’s Problem Find a geometric explanation for the apparent motion of the planets n n n Apparent backward motion against the stars Changing brightness Changing speed (speeds up and slows down)

“The Crystalline Sphere” Aristotle (Student of Plato, 384 - 322 BCE) The stars and planets are spheres, made of an ethereal substance that move in circles around a central earth.

Ptolemy’s model consisted of a series of concentric spheres, with the Earth at the center (geocentric). The motions of the Sun, Moon, and stars were based on perfect circles. Ptolemy (85 -165 CE)

To account for the observed retrograde motion of the planets, a system of epicycles or small circular paths hold the planet, that in turn moved around larger circular orbits around the Earth.

Simplified Ptolemaic Solar System

Rebirth (Rinascenza) Italian historian Giorgio Vasari 1550 Christopher Columbus 1451 - 1506 n. A rebirth of classical learning and knowledge through the rediscovery of ancient texts, and; n. A rebirth of European culture in general. William Shakespeare 1564 - 1616 Leonardo Da Vinci’s Mona Lisa 1452 -1519

Nicolaus Copernicus 1473 - 1543 Finally we shall place the Sun himself at the center of the Universe. All this is suggested by the systematic procession of events and the harmony of the whole Universe, if only we face the facts, as they say, 'with both eyes open'. —Copernicus from "De Revolutionibus Coelestibus"

Tycho Brahe Danish astronomer, 1546 - 1601 Tycho made highly accurate (within 1/60 degree) nakedeye observations of the positions of stars and planets over many years. He proposed a compromise model in which all the other planets orbit the sun, but the sun orbits the earth.

Johannes Kepler German astronomer, 1571 - 1630 Kepler worked under Tycho during 1600 - 1601, then inherited the records of Tycho’s detailed observations. He accepted the Copernican hypothesis, but abandoned the assumption that all motions are circular.

The Orbit is an Ellipse! Focus The sun is at one focus; there’s nothing at the other.

Planets go faster when they’re close to the sun A line drawn from the sun to the planet sweeps out equal areas in equal times.

Outer planets move slower than inner planets. Time (yr) Radius (AU) (Time)2 (Radius)3 Mercury 0. 24 0. 39 0. 058 0. 059 Venus 0. 61 0. 72 0. 37 Earth 1. 00 Mars 1. 88 1. 52 3. 53 3. 51 Jupiter 11. 86 5. 20 140. 7 140. 6 Saturn 29. 46 9. 54 867. 9 868. 3 (Time in years)2 = (Radius in AU)3

Kepler’s Laws 1. 2. 3. Orbits are ellipses, with sun at one focus. Equal areas in equal times (faster when close to sun) (Time in years)2 = (Radius in AU)3 Bottom line: The universe speaks math!

Galileo Galilei Italian scientist, 1564 - 1642 Made one of the first telescopes, and pointed it at the heavens. . .

Siderius Nuncius (The Starry Messenger) Venice, 1610 (Written in Italian, not Latin!)

Lunar topography. . . Sunspots. . . The Moon is not a smooth and perfect sphere.

New “planets” orbiting Jupiter. . . At least some planets don’t orbit the earth; and earth isn’t the only planet with a “moon”!

What happened to Galileo? n n n He became famous (not just among astronomers). He started advocating (teaching) Copernicanism (and ridiculing those who disagreed) Condemned by the Church, placed under house arrest and forced to recant his beliefs (not really).

Isaac Newton English scientist and mathematician, 1642 - 1727

Newton’s Accomplishments n Newton’s Laws of Motion n Inertia (mass) Force Action/Reaction Gravity (a phenomena of mass) n Lenses (made an improved telescope using mirrors rather than lenses) n Calculus – the mathematics to determine how things change. n

Caroline & William Herschel Cataloged the sky Sky maps containing nebulae, galaxies, nova 1738 - 1822 Telescope through which Uranus was first observed. 1750 - 1848 40 foot x 50 inch Largest in the world in 1800

Our 30 Closest Stars Alpha Centauri Barnard’s Star