Ancient Astronomy

Astronomy – the most ancient of the sciences

Astronomical records back to prehistoric times

Scientific Methods —Common Steps

1. Recognize a question, a puzzle, or an unexplained fact.

2. Make a hypothesis (educated guess) to resolve the puzzle.

3. Predict consequences of the hypothesis.

4. Perform experiments or make calculations to test the predictions.

5. Formulate the simplest general rule that organizes the three main steps.

The Scientific Attitude

The scientific attitude is one of• inquiry.

• experimentation.

• willingness to admit error.

The Scientific Attitude• Fact is a close agreement by

competent observers who make a series of observations about the same phenomenon.

• A scientific hypothesis is an

educated guess that is only presumed to be factual until supported by experiment.

Which of these is a scientific hypothesis?

A. The Moon is made of green cheese.

B. Atomic nuclei are the smallest particles in nature.

C. A magnet will pick up a copper penny.

D. Cosmic rays cannot penetrate the thickness of your textbook.

The Scientific AttitudeCHECK YOUR NEIGHBOR

Which of these is a scientific hypothesis?

A. The Moon is made of green cheese.

B. Atomic nuclei are the smallest particles in nature.

C. A magnet will pick up a copper penny.

D. Cosmic rays cannot penetrate the thickness of your textbook.

The Scientific AttitudeCHECK YOUR NEIGHBOR

Explanation: All are scientific hypotheses! All have tests for proving wrongness, so they pass the test of being a scientific hypothesis.

Oldest star chart- 32,000 years ago (Orion?)

Stonehenge – 3100 – 2100 BC

Great Pyramid at Khufu (Cheops) – 2600 B.C.

Aligned within 1/20 degree of true north

Possible correlations with astronomical objects?

Chichen Itza – Mayan observatory

Medicine Wheel – Northern Wyoming

Chaco Canyon – supernova of 1054?

Chaco canyon – Anasazi sun dagger –

A.D. 400-1300, marks summer solstice

Constellations

Apparent groupings of stars – relatively fixed positions

Constellations – the 88 semi-rectangular regions that make up the sky

Star trails

Star trails around South Celestial Pole (Gemini Observatory, Chile)

Most of modern astronomy and cosmology comes from the Greeks

Celestial Sphere

The Geocentric View

Aristotle’s View: The Most Perfect Form is the Circle

The Crystalline Spheres

The Motion of the The Motion of the EarthEarth Parallax: The apparent motion of an Parallax: The apparent motion of an

object due to the motion of the object due to the motion of the observer.observer.

The Greeks could not detect any The Greeks could not detect any parallax for the stars (or planets).parallax for the stars (or planets).

Conclusion:Conclusion:– The Earth is not moving.The Earth is not moving.

OROR– The Stars are too far away to measure The Stars are too far away to measure

parallax with crude instruments / eye.parallax with crude instruments / eye. The Greeks chose not moving.The Greeks chose not moving.

Correct Method - Wrong Conclusion

AristarchusAristarchus 310 - 230 BC310 - 230 BC

Heliocentric modelHeliocentric model

Determined relative distances Determined relative distances betweenbetween

Sun and MoonSun and Moon

The Distance to the The Distance to the SunSun Aristarchus measured Aristarchus measured to be 87 degrees to be 87 degrees Sun Distance = 19 Moon DistanceSun Distance = 19 Moon Distance (today: Sun is about 400 times further away than moon)(today: Sun is about 400 times further away than moon)

Aristarchus of Samos ~ 310 - 230 BCE

First Quarter Moon

Third Quarter Moon

α

Ptolemy

(85 – 165 A.D)

Lived in Egypt, probably Alexandria

Summarized Greek astronomy in the Almagest

Geocentric model of solar system

Epicycles and EquantsEverything circles something else…

Very complicated – but it worked! (sort of)

http://astro.unl.edu/naap/ssm/animations/ptolemaic.swf

http://astro.unl.edu/animationsLinks.html#ca_renaissance

Major assumptions of the Ptolemaic model

– All motion in the heavens is uniform circular motion.

– The objects in the heavens are made from perfect material, and cannot change their intrinsic properties.

– The Earth is at the center of the Universe.

After the Greeks:

• Alexandria burns in 272 A.D., Roman empire collapses, and Europe enters Dark Ages

• Roman Catholic Church combines Ptolemaic with Aristotelian thought into official church doctrine – Earth as immovable center of cosmos

• Much of astronomy is carried forth by Persian and Islamic astronomers who preserved Greek thought and refined it – named many stars we know today

Breaking through the old model…

Major problems with the Ptolemaic System:

It failed to….

Accurately predict eclipses (off by hours, days, etc…)

* Predict position of planets accurate enough

*Couldn’t explain meteors, comets, supernovae

Nicolas Copernicus (1473-1543) – proposed heliocentric hypothesis, mostly on philosophical grounds

Copernicus’ model:

• Gave similar predictions to Ptolemaic model, also used epicycles, etc…

• Proposed earth rotates on axis to cause night and day

• Proposed earth and other planets travel around sun

• Radical idea for time –this sounded crazy to most people!!!

De Revolutionibus Orbium Coelestium, 1543

(On the Revolutions of the Heavenly Spheres)

Copernicus’ explanation of retrograde motion

Galileo1564 - 1642

• All bodies fall at same rate!! - Tower of Pisa

Galileo’s Telescope• Galileo’s telescopic observations led

him to firmly reject the geocentric model.

The Milky Way was composed of The Milky Way was composed of millions of stars.millions of stars.

He realized that wherever he looked, he saw more and more stars……

SaturnSaturnGalileo noticed….“Saturn has ears”

SunspotsSunspotsA. A. The surface of the Sun was imperfect.

B. apparent motion of the spots across the Sun's disk implied rotation.

• Detailed moon drawings – the moon is not a smooth sphere!

The Galilean Satellites

• They Orbit Jupiter!•So Why Cannot the Planets Orbit The Sun

The Phases of VenusThe Phases of Venus Galileo noticed that when Venus wanes (becomes crescent), it becomes larger.

The Phases of Venus