ASTRONOMY The study of the universe

Chinese Observation Observation and record keeping goes back more than 4000 years. solar eclipses. Of particular interest to early Chinese astronomers were solar eclipses. An astronomical tool that was especially important to early Chinese astronomers was the gnomon. A gnomon is simply an object—a post stuck in the ground, for instance— whose shadow is used to record the changing position of the Sun. Who were some of the earliest astronomers?

BABYLON and SUMERIA 3000BC The astronomers of Babylon were a special group of scribes who observed the movements of the stars and planets. The astronomers had many different responsibilities. They recorded their observations about the daily, monthly and yearly position of the stars and planets. They advised the king about how their observations affected the calendar. And they advised the king about how omens seen on earth or in the skies might effect future events. scribesomens Newly translated Babylonian texts indicate that positions and motions of the stars and planets were calculated instead according to complex equations inherited from the Sumerian civilization. The Babylonians seem not to have understood the theoretical basis of these formulas, only how to use them. The Sumerians had even more exact knowledge of the solar system and its place in the universe than their Babylonian heirs, whom they predate. Their calendar, devised as early as 3000 B.C., is the model for our calendar today, and they evidently understood a number of more arcane astronomical matters.

STONEHENGE STONEHENGE ENGLAND 2900 BC Was used to identify the first day of summer. Ancient astronomers could use it like a giant gunsight to determine when the sun was rising in a certain direction.

Accurate calendars 2400 BC EGYPTIAN Astronomy

The Aztec “ Sun Stone” Calendar of the Aztec people of Pre-Columbian Mexico. Stone's year of creation, 1479 CE. Measures about 3.6 meters (12 feet) in diameter, 1.22 meters (4 feet) in thickness and weighing 24 tons, [ [

"El Caracol" at Chichén Itzá --an observatory of the Maya and Toltec. The Maya were expert sky- watchers Buildings aligned with solstices, equinoxes, the moon, or planets. Center of the Yucatán Peninsula present-day Mexico.

The Aztec calendar wheel is represented by 13 months of 20 days each, as determined by the movement of the Sun, Moon, and stars. ©Library of Congress

Aristotle Aristotle 300 BC Famous Greek philosopher Logic thinking Scientific teachings used for over 1000 years

EarthEarth, Water, Air, Fire,WaterAirFire AetherAether, which is the divine substance that makes up the heavenly spheres and heavenly bodies (stars and planets).heavenly spheres Each of the four earthly elements has its natural place. All that is earthly tends toward the center of the universe, i.e., the center of the Earth. Water tends toward a sphere surrounding the center. Air tends toward a sphere surrounding the water sphere. Fire tends toward the lunar sphere (in which the Moon orbits). When elements are moved out of their natural place, they naturally move back towards it. This is "natural motion"—motion requiring no extrinsic cause. So, for example, in water, earthy bodies sink while air bubbles rise up; in air, rain falls and flame rises. Outside all the other spheres, the heavenly, fifth element, manifested in the stars and planets, moves in the perfection of circles.

Ptolemy (c.85-c.165) A GREEK ASTRONOMER Believed the planets and sun orbit the Earth. GEOCENTRIC- “Earth Centered” The order: Mercury, Venus, Sun, Mars, Jupiter, Saturn. This system became known as the Ptolemaic system.

Copernicus ( ) the founder of modern astronomy His theory had the sun in the center of the solar system HELIOCENTRIC- “Sun Centered” asserted that the earth rotated on its axis once daily and traveled around the sun once yearly:

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BRAHE Made an extremely accurate star catalogue of over 1000 stars. He showed the moons orbit is not a perfect circle.

ellipses realized that the orbits of the planets were not circles, but instead "flattened circles" called ellipses KEPLER ( )

Crafted his own telescope Discovered: that our Moon has craters, Jupiter has its own moons, the Sun has spots GALILEO GALILEO 1564 to 1642

Sir Isaac Newton ( ) Defined the Laws of Motion and Universal Gravitation. Now our solar system makes sense!