The Ordered Universe

The Birth of Modern Astronomy

(Trefil & Hazen, The Sciences, Ch 2)

Homer’s “Bear that never bathes”

Stonehenge

…one of several old “time-reckoning” machines. It’s moving parts are in the sky.

Ancient astronomy

Great Pyramid of Giza

…was aligned to the pole star, and it was possible to read the seasons from the position of the pyramid’s shadow.

The Mayans of Yucatan

…inscribed stone monuments with formulae for predicting solar eclipses

Plains Indians

• Recorded the rising points of the bright stars, to record seasonal grazing patterns.

Political Power

…Columbus influenced native people to provide food for his crew by warning of “an inflamed and angry moon.”

Brief Overview of Early Science

• Greece, 4th C B.C.• Roman Empire Fell,

5th C A.D.• Chinese, Polynesians,

Arabs• Islamic influences in

Spain 10-12th C

• Universities emerge in Europe, 13th C

• Printing press, 15th C• Copernican hypothesis

heliocentrism 15th C• Galileo and “scientific

method” 17th C

The Ordered Universe

Part 1:

Ancient Astronomers

Ancient China

• Working calendar 13th Century B.C.!

• Star Catalog with 800 entries, 350 B.C.!

• Observed comets and supernovas

Babylonian Astronomy

• Oldest scientific documents

• 800 B.C.• Record eclipses,

positions of planets and rise/setting of the Moon

Greek Astronomy600 B.C. to 200 A.D.

• Thales introduced geometrical ideas into astronomy.• Pythagorus universe as a series of concentric spheres• Eudoxus the idea of rotating spheres to account for the

observed complexities of planetary motions.• Aristotle correct explanation of lunar eclipses; sound

argument for the spherical shape of the earth.

Astronomy at Alexandria 3rd Century B.C.

• Aristarchus• Determined size and

distance of Sun and Moon rel to Earth

• Developed 1st heliocentric model

• Eratosthenes• Made accurate

calculation of the size of the Earth

Claudius Ptolemy

• Greek astronomer from 2nd Century, proposed first enduring theory of the universe, an Earth-centered or Geo-centric model.

Occam’s Razorand interpreting oddities

• 14th Century English Philosopher

• Given a choice, the simplest solution to a problem is most likely to be right.

Stonehenge

2

Figure 2-1

Stonehenge is built so that someone standing at the center will see the Sun rise over the heel stone on midsummer’s morning.

4

Figure 2-3

One puzzling aspect of the construction of Stonehenge is the raising of the giant lintel stones. Three steps in the process were probably (a) to dig a pit for each of the upright stones; (b) to pile dirt into a long sloping ramp up to the level of the two uprights so that the lintel stones could be rolled into place; and (c) to cart away the dirt, thus leaving the stone archway.

The Ordered Universe

Part 2:

Birth of Modern Astronomy

The “Fab. Four”

Copernicus, Brahe, Kepler, Galileo

Figure 2-5

The Ptolemaic (a) and Copernican (b) systems both assumed that all orbits are circular. The fundamental difference is that Copernicus placed the Sun at the center.

(a) (b)

Mikolai Kopernik, 1473

• Copernicus outlined a theory for a sun-centered or “heliocentric” universe

• 1543, On the Revolutions of

the Spheres

Tycho Brahe,1546-1601

Johannes Kepler, 1571-1630

Kepler’s Laws

• Planets orbit the sun in an ellipse.• planets move more rapidly when close to

the sun and more slowly when distant from the sun

• The cube of the mean distance of each planet from the sun is proportional to the square of the time it takes to complete one orbit

Check your neighbor…

• Summarize key ideas of our attempt to make sense of the universe– Ancients of China, Egypt, Greece

– Aristarchus

– Eratosthenes

– Ptolemy

– Copernicus

– Brahe

– Kepler