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AstronomyPhys 181-701

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“That’s no moon…That’s a space station!”Obi Wan Kenobi – STARWARS

“The sun, with all those planets revolving around it and dependent on it, can still ripen a bunch of grapes as if it had

nothing else in the universe to do.”Galileo Galilei

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ASTRONOMYThe study of matter and

energy in our Universe and its evolution over time.

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Early Observations The Sun and Moon

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ECLIPSES

GREEK ~ ekleipsis

Abandonment•580’s B.C. Herodotus reports that a war between the Lydians and the Medes was ended by a solar eclipse that took both armies by surprise during a battle.

•1504 Christopher Columbus convinced Jamaicans to aid him by threatening that the Christian god would swallow the sun in anger, and event which then proceeded, right on schedule.

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SHADOWSShadows

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Eclipse Facts1. Moon and sun have roughly the same angular size.

2. Lunar eclipses last about 1 h 45 min (total).

3. Moon’s umbral shadow on the Earth is no wider than 167 mi…Thus solar eclipses last no more than 7 min 30 sec.

4. Total eclipses occur every 18 yr 11 days.

5. On the average, a given location may witness a lunar eclipse nearly every year and a partial solar eclipse nearly every other year, but a total solar eclipse only about once every four centuries.

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Totality

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Diamond Ring

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Moons Umbra

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Anular Eclipse

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Lunar ObservationsLUNAR OBSERVATIONS

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Moon Phases

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What time is it?

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ANALEMMA

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Size of the earthEratosthenes 240 B.C.

Estimating the size of the Earth

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The Motion of the Planets Around the Sun

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Plato ~ 400 B.C.

Motion of the planets in the skyMust be explained.

Models must have these features:

1. Must be mathematical2. Must explain observations3. Must be based on the perfection of circles4. Must obey Aristotelian Physics

Ancient Astronomers

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AristotleAristotelian Physics

An object will not move unless some influence causes its motion.

Conversely, the absence of such an influence would render an object

motionless.

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The consequence of the Aristotelian view is that the Earth can not be in motion because the influence producing such motion would be felt.

His chemistry was just as bad…

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Stellar Parallax

Sought but not observed until 1838

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AristarchusAristarchus: Relative Distances

and Sizes of the Moon and the Sun ~ 220 B.C.

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PtolemyPtolemy 150 A.D.

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Retrograde Motion

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In 640 A.D., after a 14 month siege by Arabs, the great city and library of

Alexandria fell.

The Arabs recognized the value of the Almagest and continued to develop

mathematics and astronomy.

In Europe, much knowledge was lost and the west was consumed by the Dark Ages…

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IMPORTANT

• Eclipse Frequency• Moon Phase Tells Time• Aristotelian Physics• Stellar Parallax• Plato Describes Features of Model• Retrograde Motion & Ptolemy’s

Model

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Next time…..

THE COPERNICAN REVOLUTIONTHE COPERNICAN REVOLUTION