Timeline Project Make a group of 3 people and decided who is presenting to the class and who will be the back up if they are not here Pick one of the individuals or cultures that contributed to ancient astronomy Information that needs to be on your poster – Name of group members and job assignment – Era of influence, for the person or culture – What was there contribution to astronomy – What influence does it have in the Modern world

Chapter 3 Ancient Astronomy I will be able to explain how ancient civilizations/people teach us about astronomy

Chapter Opener

Mesopotamian Astronomy First to keep records, built observatories called ziggurats Ziggurats had 7 terraces: Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn Had 4 constellations, one for each season. Eventually had 12, one for each month Calendar was 360 days long, would cycle 12 and 13 month years to keep seasons in order Created the 360 degree circle, 60 minutes, 60 seconds and the 0 symbol for degrees.

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The Babylonians 500 BC started to notice some cycles in the moon and planets Realized how planet motion could be predicted, by knowing the cycles of each object Their strong belief in astrology is what lead them to explore these cycles The first to apply a mathematical model to the movement of celestial objects Had no interest in modeling the solar system

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Egyptian Astronomy They were more practical in the use of astronomy. Predicting farming ; growing season, Nile floods Placement of monuments, temples and other structures Astronomy was mainly mythological Influenced Greek Astronomy.

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Early Greeks Astronomy started for same reasons as other cultures in the region Records are tough to get on most & second most of the time First culture that started to use the information to explain how the universe works, without mythology Greek astronomy was wide spread across the Mediterranean region

Miletus Three famous astronomers from this city: Thales, Anaximander & Anaximenes (in Asia Minor) Thales (624 – 547 B.C.E) was instructed by the Egyptians, was looking into predicting eclipses Anaximander (611 – 547 B.C.E.) gave explanations of the movement of objects, Earth was free floating, other objects were hollow with fire inside with holes. Anaximenes (585 – 526 B.C.E) continued the mechanical explanations of the heavens, started the idea of a celestial sphere

Pythagoras 582 – 500 B.C.E Continued the development of a mechanical system for the universe – not much written so it is hard to know if it was Pythagoras or students First to place the sky on circular orbits Earth is not flat and moves in a circle around a central fire This movement made a great deal of sound Made celestial objects circular

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Eudoxus 408 – 355 B.C.E : born in Asia minor moved to Athens ; studied under Plato Tried to explain the retrograde motion of planets using Pythagorean ideas Object would spin on multiple circles to account for their motions across the sky He did not explain the change in light from object – tied to their distance from Earth Also failed to explain why retrograde motion was not always the same.

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Aristotle Lived B.C.E., A student of Plato Accepted Eudoxus model and added some more circles, only motion that is repeatable and suitable for unchanging objects like the sun and moon He Held Pythagorean view of circular celestial objects…gave proofs (next Slide) Also accepted and added to Empedocles (494 – 434 B.C.E.) 4 elements idea: fire, earth, wind and water. Stated that they fall to their natural place and since earth is the heaviest it is at the center

Aristotle Proofs All objects fall down toward the center of a sphere, if Earth was another shape this would not be the case If the Earth was another shape we would see this cast on the moon during a lunar eclipse. If the moon was not a sphere we would not see the phases of the moon If the Earth was flat we would see all the stars from every location Was not an Astronomer but his ideas had an influence for almost 2000 years and some are still relavent today

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Later Greeks Greeks had developed a model of celestial motions After Aristotle they began to apply geometrical principles to the model Over the next 500 years they discovered important concepts on the size, shapes and distances They fine tuned the model of the solar system The big four Aristarchus, Eratosthenes, Hipparchus and Ptolemy

Aristarchus After Euclid wrote his book on geometry, Aristarchus applied them to astronomy Showed that the size and distance of celestial objects could be determined His method involved taking the moons angular measurement – directly Then using the linear measurement – that is taken during an eclipse – cylinder versus sphere Look at diagrams on page 46 Works well if all objects are the same distance

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Aristarchus Hipparchus later improved the method and was able to show the moon was at 59 earth radii (60 earth radii) Aristarchus also said the distance to the sun could be found by using the first and last quarter moon Figures on page 47 – angle estimated at 87 degrees – the closer the lower the angle – farther closer to 90 Estimated at 19 times the distance of earth to moon distance – accepted for 2000 years

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Aristarchus Problems – Impossible to measure the angles in his time Did show the universe was larger then it was believed at the time He calculated the size of the Sun. It was so large that he moved it to the center The rotation of the Earth would cause objects to fall at an angle, great winds to constantly blow and stars would dim as we revolved around the sun

Eratosthenes Calculated the diameter of the earth Sent an assistant to Syene (a city to the south of Alexandria) and he reported that the sun’s light hit the bottom of a pit at noon on summer solstice Discovered that the distance between the two cities was 1/50 th of the earth’s diameter Accuracy is the only real problem (25,000 miles)

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Hipparchus Lived on the island of Rhodes – most of his work was lost He improved the measurements of distance for the moon and sun; length of the year, improved the star catalogs and theories on sun and moon motion Started cataloging stars in 134 B.C., may have had close to 850 stars in it, compared his work to earlier astronomers and found a 2 degree change over time – this was precession Vernal equinox shifts by 1 degree every 78 years Estimated precession at 360 degrees every 28,000 yr

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Ptolemy Claudius Ptolemaeus worked in Alexandria from 127 – 151 A.D. He developed the latitude and longitude system, put North on the top and east on the right of maps He also improved the measurements of distance for the sun and moon He cataloged over a thousand stars and their brightness – a system we still use today Some of this may have been Hipparchus work

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Ptolemy Refined the geocentric model, moved earth to off center yet still unmoving – used same argument as Aristotle Changed the shape of the orbit (deferent) to an ellipse and gave every planet on an orbit an epicycle or a circle on a circle path This means that objects did not have a uniform speed or distance from earth point of view Stood for 1500 years, no one looked into it again for 1000 years

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Chinese Astronomy Started recording data as far back as 1300 century B.C. Recorded over 900 solar eclipses and 600 lunar eclipses over 2600 years The also had entries for meteor showers, super novas, and comets (Halley being one of them) The super nova and comet data has been helpful to modern astronomy It was also used for the same purposes as Mesopotamia and Greeks

Mesoamerican Astronomy Mayan was the strongest in astronomy and flourished between 0 A.D. and 1000 A.D. Venus was identified with an important god in both Aztec and Mayan culture, battles were timed with positions of this planet They had extensive tables that predicted the movements of Venus, lunar and solar eclipses Their calendar used all three of these objects to keep it in order Most data lost to the world due to Spanish Conquest