PHSC 1053/3053: Astronomy Historyfaculty.atu.edu/jrobertson/courses/PHSC1053/PHSC1053... ·...

Astronomy is perhaps the oldest science. – Stargazing probably came before our use of…

• language • fire • tools

• What is out there? • How does it all work? • How do we know what we know? • What is its past? What is its future? • What is “our” place in the universe? • How do we fit in?

PHSC 1053/3053: Astronomy History

Ancient Roots of Science

• How is modern science rooted in ancient astronomical observations?

• Describe several impressive ancient astronomical accomplishments.

Astronomical Event Recorded

Ancient Astronomy • Many cultures throughout the world practiced

astronomy.

• They made careful observations of the sky.

• Over a period of time, they would notice the cyclic motions of: – Sun – Moon – planets – celestial sphere (stars)

Stonehenge • Stonehenge (England) Sunrise on the summer solstice as seen looking east.

Stonehenge (completed 1550 BC)

• If you stand in the middle: – the directions of sunrise &

sunset on the solstices is marked. – the directions of extreme moon

rise & set are marked.

• The Aubrey holes are believed to be an analog eclipse computer.

• Many other alignments are verified by astronomical planetarium computer simulations

This famous structure in England was used as an observatory.

Observatories • Big Horn Medicine Wheel (Montana) • Chichen Itza Mayan Caracol (Mexico)

Caracol • Located at Chichen Itza, Yucatan, Mexico, the

Caracol Tower was built about 1000 AD.

• It has some solstice and equinox alignments, and also some star alignments. More interesting are the apparent alignments with Venus (one of their "gods").

• Mayan tablets also mention the rising of Venus. The alignments make sense in light of the written records.

Caracol

Mayans (fl. A.D. 400 – 1200)

• lived in central America

• accurately predicted eclipses (~19 year cycle!)

• Venus was very important Mayan mathematics

– base 20 system – invented the concept of “zero”

the Observatory at Chichén Itzá

Big Horn

Big Horn • The Big Horn Medicine Wheel in the Big Horn Mountains

near Sheriden, Wyoming was interpreted in 1974 as an indicator of summer solstice sunrise and sunset, with other alignments for the rising of certain stars (Aldebaran, Rigel, and Sirius).

• Built about 1050 AD. Has 28 spokes, and is about 90 ft in diameter.

• About 50 similar circles exist. The oldest is in Canada (built about 2500 BC - at the same time as the Egyptian pyramids).

Sun Dagger and Aztec Calendar Stone

Sun Dagger • Discovered in 1977.

• Anasazi Indians of Chaco Canyon, New Mexico constructed a spiral

rock carving on Fajada Butte.

• At noon on the summer solstice, a dagger of sun penetrates the center of the spiral.

• On the autumnal equinox, a sun dagger passes through the center of a small spiral on the left, and another passes on the edge of the large spiral. At the Winter Solstice, a big sun dagger passes on either side of the large spiral.

• Also marks a 19-year lunar cycle. (The spiral has 19 rings.)

Why did they do it? • archeologists & anthropologists surmise:

– to keep time – for agricultural purposes – for religious purposes

• As far as we can tell, none of these ancient cultures

tried to build a physical model based on their observations.

• Instead, they created myths to explain the motions of the objects in the sky.

• Science seeks explanations for observed phenomena that rely solely on natural causes.

• Science progresses through the formulation and testing of models of nature that explain the observations as simply as possible with the least amount of complexity. ! Occam’s Razor

• A scientific model must be testable and make predictions that can also be tested. This may force us to revise or abandon the model.

Hallmarks of Good Science

a model that survives repeated testing, experimental verification and allows accurate predictions to be made.

Theory

Bad Scientific Practice • pseudoscience – masquerades as science, but

does not follow the scientific rules of evidence.

• nonscience – establishes truths through belief or conviction

Astrologer/Astronomer • In the ancient world Astronomers paid their bills and funded

their pursuits by – predicting astronomical events for nobles (making them seem both

knowledgeable and therefore wise and powerful) • eclipses • tides • comets • planetary motions

– casting horoscopes, predicting fortunes – entertainment

• Astrology, although totally bogus, was good economics!

Astrology • claims to study how the positions of the Sun, Moon, &

planets among the stars influence human behavior

• was the driving force which advanced ancient astronomy

• Kepler & Galileo were the last astronomers to cast horoscopes… since then astronomy grew apart from astrology into a true science

• modern scientific tests of astrology fail …it is a pseudoscience

Astronomy Versus Astrology Astrology is an ancient superstition that hold that a person’s personality

and actions are influenced by the positions of the sun, moon, planets, and stars at the moment of birth. In addition, astrologers claim that the daily changes in the location of heavenly bodies can influence events in our everyday lives. All of this is summarized in a horoscope, which includes a diagram of the zodiac, showing the precise positions of the heavenly bodies in their orbits.

Is there any physical reason we should expect astrology to work, except

that it might appeal to our needs? There seems to be no way for the various heavenly bodies to interact on the body of a baby at birth, except via gravity. The force of gravity exerted on the baby by the doctor is many times larger than that of the sun and planets. Thus, it would seem more important where the doctors and nurses stand in the room rather than the orientation of the sun, moon, mars and the earth.

Astronomy Versus Astrology Is there any evidence that astrology does work? Astrology has been

tested many times over, and no legitimate test has proven any astrological influence on our lives. Extensive tests have searched in vain for relationships between birth date and profession, blood type, handedness, divorce rate, etc.

Yes it is based on science: Positions via Celestial Mechanics It is NOT a science. It can not make accurate, verifiable predictions. NO it doesn’t influence our lives: Use it like you would flipping a coin

or for entertainment along with the Sunday Funnies or fortune cookies.

Ancient Astronomers (Astrologers)

Arab Astronomers at work keeping the nobles informed and entertained. A mix of science and pseudo-science.

What have we learned? • How is scientific thinking similar to other

everyday thinking? • Scientific thinking involves trial and error like much

other everyday thinking, but in a carefully organized way.

• How is modern science rooted in ancient astronomical observations? • Ancient cultures observed the motions in the sky for

religious and practical reasons. Science took root as they eventually sought to understand the patterns they had discovered.

Astronomy Versus Astrology TOP 10 • 10. Astronomers never try to contact dead Astrologers.


• 9. Politicians wives never ask astronomers for advice.



• 8. The positions of the stars, planets, etc. dictate an

astronomer’s evening observing schedule, but they dictate ALL aspects of an astrologer’s life.





• 7. Telescopes come in a staggering array of shapes and sizes. All Ouija boards look the same.





• 7. Telescopes come in a staggering array of shapes and sizes. All Ouija boards look the same.

• 6. No Astronomer has a 900 number.

Astronomy Versus Astrology TOP 10 • 5. Your VISA limit is of very litter interest to an

astronomer.


astronomer. • 4. Astronomers occasionally make accurate predictions.


astronomer. • 4. Astronomers occasionally make accurate predictions. • 3. Alcohol makes complex astronomical concepts more

difficult to comprehend. It makes astrological concepts easier.




• 2. Transposing two astronomical objects’ coordinates makes a huge difference. Transposing two peoples’ horoscopes makes no difference at all.




• 2. Transposing two astronomical objects’ coordinates makes a huge difference. Transposing two peoples’ horoscopes makes no difference at all.

• 1. Astronomers believe in the truth of relativity. Astrologers believe in the relativity of truth.

The Scientific Method

Iterative Logic and Creativity

“Right-brain” thinking “Left-brain”

thinking

Science Questions • Science is only interested in questions that have an

experimentally verifiable end.

• There must be a Test for wrongness or rightness.

• If there is nothing experimentally verifiable, there is no science.

• Not interested in speculations, only what can and can not happen.

• Beware Pseudo-Science (Astrology) • Extraordinary Claims Require Extraordinary Evidence!

Claudius Ptolemy (AD 100-170) Almagest

– star catalogue and atlas with brightness assignments – measurement instruments – motions & model of planets,

Sun, Moon (geocentric)

His model fit the data, made accurate predictions, but was horribly contrived!

Aristotle’s Perfect Spheres

Our Place In the Cosmos Aristotle and Ptolemy Geocentric Theory (Earth Centered View) Copernicus and Galileo Heliocentric Theory (Sun Centered View)

How does one explain retrograde motion?

Over a period of 10 weeks, Mars appears to stop, back up, then go forward again.

Movie. Click to play.

The Enigma of the Planets

The position of Mars observed against the background stars over many weeks. Planos ~ wanderer

The retrograde loops of other planets over the course of years, shown against the background stars.

Epicycles Attempting to explain planetary motion in a geocentric model of the universe using perfect circles was not easy. Just ask Kepler.

Geocentric Solar System This allowed the earth to be stationary in space, in the center of the universe, and would describe some of the motions of the heavens, though not very accurately.

Retrograde Motion • Mars Retrograde Motion

• Epicycles (Geocentric View)

Eratosthenes Lived in Alexandria Egypt at the height of its glory as the center of intellectual learning and knowledge in the ancient world. He learned from a friend, of a water well in Syenne Egypt, near Aswan to the south. On a certain day of the year, the city celebrates summer. On that day at noon, the sun does not cast any shadows and you can see sunlight reflected from the bottom of most water wells. Eratosthenes knew that no such day existed in his town of Alexandria further north.

Models and Experimental Verification The earth is round? The earth moves? Ludicrous?! Eratosthenes Knew

The moon and sun are round. During lunar eclipses, earth’s shadow on the moon is round.

Models and Experimental Verification How big is the earth. How fast is it going? Eratosthenes Knew

The moon and sun are round. During lunar eclipses, earth’s shadow on the moon is round. Ships at sea appear mast first and disappear mast last indicating

curvature.

Sailing, sailing, over the ocean blue... Eratosthenes Knew

The moon and sun are round. During lunar eclipses, earth’s shadow on the moon is round. Ships at sea appear mast first and disappear mast last.

Sailing, sailing, over the ocean blue... The earth must be round? Eratothenes Knew

The moon and sun are round. During lunar eclipses, earth’s shadow on the moon is round. Ships at sea appear mast first and disappear mast last.

Hire a Runner to Step out the Distance Stadia (unit of measure ~ football field (Roman Coliseum))

Size of the Earth 3600 = Circumference of the Earth 70 Distance from Alexandria to Syenne What is the distance from Alexandria to Syenne?

Eratosthenes (276 - 195 BC) • He measured the circumference of the Earth. • The Sun is at the zenith in the city of Syene at noon on the summer solstice. •But at the same time in Alexandria, it is 7° from the zenith.

• Eratosthenes inferred that Alexandria was 7° of latitude north of Syene. • The distance between the two cities is 7/360 times the Earth’s circumference. • His result of 42,000 km is very close to the right number: 40,000 km.

Earth As A Sphere Circumference of the earth = (360/7) 50,000 = 24,000 miles For π ~ 3 and D = 2 x Radius 2 π R = 24,000 R = 24,000/6 R ~ 4,000 miles Radius of the Earth

Scientific Analysis Eratosthenes had measured the size of the earth to within 10% of the actual value. Quite a feat. But, science is not only about answering a question (how big is the earth?), but following up on the consequences of the theory or model. If the earth is a sphere with a radius of 4,000 miles, what are the consequences?

Consequences Perhaps we can not believe the earth is flat. It must be a sphere. But, at least let us believe it sits motionless at the center of the universe with the stars and planets revolving around us. OTHERWISE… Distance = Speed x Time Distance = Circumference Speed = v Time = period of rotation

Consequences Perhaps we can not believe the earth is flat. It must be a sphere. But, at least let us believe it sits motionless at the center of the universe with the stars and planets revolving around us. OTHERWISE… Distance = Speed x Time Distance = Circumference Speed = v Time = period of rotation D = 24,000 t = 24 hours

Calculating Rotation Speed D = v t 2 R π = v t 2 (4,000 miles) 3 = v (24 hours)

Calculating Rotation Speed D = v t 24,000 miles = v 24 hours 24,000 miles = v 24 hours v = 1,000 miles/hour DO YOU FEEL FAST?!

Predictions Spherical, Rotating Earth: Someone at the equator must move at 1,000 miles/hour. Experimental Verifications of the Rotating Earth:

– Focault Pendulum

– Coriolis Effect

– Planetary Motions

DEFENDER OF COPERNICAN HELIOCENTRIC THEORY I. Craters on the Moon (imperfection) II. Sunspots on the Sun (imperfection and solar rotation) III. The Moons of Jupiter (earth is not the center of all things) IV. The phases of Venus I-III Represent Circumstantial evidence IV Smoking Gun: undeniable unrefutable proof

Galileo’s Observations

Galileo’s Phases of Venus Heliocentric Geocentric

Galileo and the Inquisition

Real Retrograde Motion • Mars Motion (Heliocentric Theory)

Galileo’s observation of the phases of Venus was the final evidence which buried the geocentric model.

Geocentric Heliocentric

No gibbous or full phases! All phases are seen!

Galileo observed all phases!

Heliocentric Retrograde Motion of Mars

Summary • Ancient Observatories

• Astronomy and Astrology

• Geocentric versus Heliocentric Views of the Cosmos

PHSC 1053/3053: Astronomy Historyfaculty.atu.edu/jrobertson/courses/PHSC1053/PHSC1053... ·...

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