Upon Whose Shoulders We Stand: A History of Astronomy Up to 200 A.D. Astronomy DSA.

Upon Whose Shoulders Upon Whose Shoulders We Stand: A History of We Stand: A History of

AstronomyAstronomyUp to 200 A.D.Up to 200 A.D.

Astronomy DSAAstronomy DSA

Who were these Who were these ““ancient ancient astronomers?astronomers?””

Where did Where did ““realreal”” astronomy begin? astronomy begin? What did we know about astronomy What did we know about astronomy

2000+ years ago? 2000+ years ago? Who discovered some of our basic Who discovered some of our basic

principles of astronomy—and how did they principles of astronomy—and how did they do it? do it?

What tools did they use What tools did they use ““back thenback then””?? Why did they get into astronomy?Why did they get into astronomy? When were maps of the sky created?When were maps of the sky created? When were constellations When were constellations ““inventedinvented””??

Why was astronomy important?Why was astronomy important?

CalendarsCalendars Planting/Farming depended upon the Planting/Farming depended upon the

knowledge of the seasonsknowledge of the seasons Religion/ AstrologyReligion/ Astrology NavigationNavigation TimekeepingTimekeeping Land SurveyingLand Surveying

Datelines:Datelines:

ChinaChina IndiaIndia GreeceGreece EgyptEgypt MexicoMexico

GeometGeometryry

RuledRuled Here Here

you you see see math & math & a beliefa belief

system system in in stonestone

Timelines:Timelines: Most of us think of Astronomy really Most of us think of Astronomy really

starting with Copernicus, Tycho Brahe, starting with Copernicus, Tycho Brahe, Galileo…..Galileo…..

But a lot of what we know today and take But a lot of what we know today and take as fact was as fact was ““knownknown”” and measured and measured thousands of years ago.thousands of years ago.

This a short history of some of those early This a short history of some of those early astronomers who reasoned and measured astronomers who reasoned and measured out a lot of the universe without out a lot of the universe without sophisticated tools—but with sophisticated sophisticated tools—but with sophisticated reasoning and mathematics.reasoning and mathematics.

ArchaeoastronomyArchaeoastronomy

The study of the astronomical sites which have The study of the astronomical sites which have left us with no written records or names of the left us with no written records or names of the people who set up the ruins that we study today. people who set up the ruins that we study today.

It is understanding how these sites were used, It is understanding how these sites were used, and the determination of what these ancients and the determination of what these ancients knew by studying the geometry and alignments knew by studying the geometry and alignments of the sites. of the sites.

ArchaeoastronomyArchaeoastronomy

What are some of the famous archaeoastronomy What are some of the famous archaeoastronomy sites?sites?

Nabta: Megalithic Site – 1000 years before Nabta: Megalithic Site – 1000 years before Stonehenge.Stonehenge.– Circle of stones marking solstices and cardinal points Circle of stones marking solstices and cardinal points

more than 6000 years ago in Southern Egypt.more than 6000 years ago in Southern Egypt.

Stonehenge: 3100 BC to 2000 BCStonehenge: 3100 BC to 2000 BC

Mesoamerican sites: 1500 BC to 1500 ADMesoamerican sites: 1500 BC to 1500 AD

Nazca Lines in Peru: 300 BC to 800 ADNazca Lines in Peru: 300 BC to 800 AD

Nazca Lines in PeruNazca Lines in Peruhttps://en.wikipedia.org/wiki/Nazca_Lineshttps://en.wikipedia.org/wiki/Nazca_Lines

History of Astronomical ScienceHistory of Astronomical Science

Starts about 600 BC in GreeceStarts about 600 BC in Greece Differs from Archaeoastronomy in that it is Differs from Archaeoastronomy in that it is

documented, written records of events. It documented, written records of events. It is reasoned out (even if wrong) theories of is reasoned out (even if wrong) theories of how things work. how things work.

It is attributable to someone/some It is attributable to someone/some learning center. learning center.

It is experiential (in most cases) with data It is experiential (in most cases) with data and observations.and observations.

Who were some of the Who were some of the ““starsstars””??

Thales of Miletus, Asia MinorThales of Miletus, Asia Minor Pythagoras of SamosPythagoras of Samos Democritus of Abdera, GreeceDemocritus of Abdera, Greece Oenopides of Khios, GreeceOenopides of Khios, Greece Aristotle of Athens, GreeceAristotle of Athens, Greece Aristarchus of SamosAristarchus of Samos Eratosthenes of Cyrene, North LibyaEratosthenes of Cyrene, North Libya Hipparchus of RhodesHipparchus of Rhodes Ptolemy of Alexandria, EgyptPtolemy of Alexandria, Egypt

Thales: 624 to 547 BCEThales: 624 to 547 BCE

Said to have predicted a solar eclipse in Said to have predicted a solar eclipse in 585 BC585 BC

Greeks already knew about the 19 year Greeks already knew about the 19 year cycle for lunar eclipses.cycle for lunar eclipses.

Measured height of the pyramids by Measured height of the pyramids by understanding understanding ““similar trianglesimilar triangle”” theory: theory: measure the shadow length at the time of measure the shadow length at the time of day when your shadow is as long as your day when your shadow is as long as your height. height.

Developed the early geometric theorems.Developed the early geometric theorems.

Pythagoras of Samos: 580 -500 BCEPythagoras of Samos: 580 -500 BCE

Invented some of the math that was Invented some of the math that was needed to get a scientific basis for needed to get a scientific basis for astronomical calculations –Pythagorean astronomical calculations –Pythagorean theorem.theorem.

First to note that the morning and evening First to note that the morning and evening stars were both Venus.stars were both Venus.

Built on Anaximander, who postulated that Built on Anaximander, who postulated that planets and stars go around in perfect planets and stars go around in perfect circles.circles.

Still geocentric thinking at his time.Still geocentric thinking at his time.

Democritus: 470-380 BCDemocritus: 470-380 BC

Developed the concept of the atom: all Developed the concept of the atom: all things were made of microscopic and things were made of microscopic and indivisible, indestructible atomic particles.indivisible, indestructible atomic particles.

He understood that the Milky Way was a He understood that the Milky Way was a large collection of stars and also thought large collection of stars and also thought that space was limitless. that space was limitless.

Oenopides: 450 BCOenopides: 450 BC

Popularized the 12 signs of the zodiacPopularized the 12 signs of the zodiac Probably copied them the Assyrians in Probably copied them the Assyrians in

MesopotamiaMesopotamia First to fix the angle of the ecliptic with the First to fix the angle of the ecliptic with the

celestial equator—called it 24 degrees.celestial equator—called it 24 degrees. Fixed the year at 365 ¼ days.Fixed the year at 365 ¼ days. Postulated the Postulated the ““Great YearGreat Year””—the number —the number

of years when the motion of the Sun and of years when the motion of the Sun and the Moon exactly repeated their motions—the Moon exactly repeated their motions—59 years59 years..

Oenopides' result leads to a lunar month Oenopides' result leads to a lunar month of 29.53013 days which is remarkably of 29.53013 days which is remarkably close to the modern value of 29.53059 close to the modern value of 29.53059

Aristotle: 384-322 BCAristotle: 384-322 BC

Did his best work on classifying plants and Did his best work on classifying plants and animalsanimals

Took a qualitative approach to scienceTook a qualitative approach to science Did not use mathematics in his studiesDid not use mathematics in his studies Earth, air, fire and water were the Earth, air, fire and water were the

elementselements Earth is immobileEarth is immobile Stars and planets use the PythagorasStars and planets use the Pythagoras’’

circular spheres modelcircular spheres model Re-discovered in the late Middle Ages, and Re-discovered in the late Middle Ages, and

used to impede observational science.used to impede observational science. Geocentrist Geocentrist

Aristarchus of Samos: 310-230 BCAristarchus of Samos: 310-230 BC

Believed in a heliocentric universeBelieved in a heliocentric universe Estimated the distance of the moon and Estimated the distance of the moon and

sunsun Utilized excellent mathematical principles Utilized excellent mathematical principles

but lacked the tools to get the but lacked the tools to get the observational data correct.observational data correct.

All of his written records destroyed in the All of his written records destroyed in the fire of the library in Alexandria.fire of the library in Alexandria.

Aristarchus Mathematical GeniusAristarchus Mathematical Genius

Aristarchus: Measuring the SunAristarchus: Measuring the Sun’’s Sizes Size

http://youtu.be/fE5WHZW3taM

Eratosthenes of Cyrene: 276-197 BCEEratosthenes of Cyrene: 276-197 BCE

Developed a map of the worldDeveloped a map of the world Developed a way to find the prime Developed a way to find the prime

numbersnumbers Estimated the circumference of the Estimated the circumference of the

earth.earth. Measured the tilt of the earthMeasured the tilt of the earth Suggested that a leap day be added Suggested that a leap day be added

to the calendar every fourth year.to the calendar every fourth year.

Eratosthenes MeasurementsEratosthenes Measurements Working in Syene and Alexandria, which Eratosthenes assumed were on the same meridian, Working in Syene and Alexandria, which Eratosthenes assumed were on the same meridian,

he estimated the distance between the cities to be about 5,000 stades (a stade is believed to he estimated the distance between the cities to be about 5,000 stades (a stade is believed to be about 559 feet - approximately one-tenth of a mile). At summer solstice, at noon, the Sun be about 559 feet - approximately one-tenth of a mile). At summer solstice, at noon, the Sun cast no shadow in Syene, but in Alexandria a shadow was visible. Using a gnomon (a vertical cast no shadow in Syene, but in Alexandria a shadow was visible. Using a gnomon (a vertical stick), Eratosthenes measured the shadow's angle to be about one-fiftieth of a circle.stick), Eratosthenes measured the shadow's angle to be about one-fiftieth of a circle.

Calculated earth radius at 4212 miles vs the 3963Calculated earth radius at 4212 miles vs the 3963 Calculated moon radius at 1478 vs. 1080 milesCalculated moon radius at 1478 vs. 1080 miles

NOT BAD for 220 BCE!!!NOT BAD for 220 BCE!!!

From “Cosmos”From “Cosmos”

http://youtu.be/tl9qIuFRIWg

Entire series available from HuluEntire series available from Huluhttp://www.hulu.com/cosmos

Hipparchus: 190 – 120 BCHipparchus: 190 – 120 BC Introduced the idea of 360 degrees in a circle.Introduced the idea of 360 degrees in a circle. Calculated the length of a year within 6.5 Calculated the length of a year within 6.5

minutes.minutes. Calculated the moonCalculated the moon’’s distance at between 59 s distance at between 59

and 67 earth radii…correct answer: 60and 67 earth radii…correct answer: 60 Discovered precession—and calculated it at 46 Discovered precession—and calculated it at 46

seconds per year (vs. the actual of 50.26 seconds per year (vs. the actual of 50.26 degrees per year.degrees per year.

Develop a star catalogue of 850 stars used later Develop a star catalogue of 850 stars used later by Ptolemy. by Ptolemy.

Developed the currently used magnitude scale Developed the currently used magnitude scale of 1-6of 1-6

Discovered the first nova.Discovered the first nova. Measured distance to moon using a Measured distance to moon using a ““parallaxparallax””

method method – Used different views of a solar eclipseUsed different views of a solar eclipse– Small angle formulaSmall angle formula– Distance ~240,000 milesDistance ~240,000 miles

Hipparchus: Distance to the moonHipparchus: Distance to the moon

Hipparchus: Distance to the SunHipparchus: Distance to the Sun

Claudius Ptolemy: 85-165 ADClaudius Ptolemy: 85-165 AD

Developed the most sophisticated model Developed the most sophisticated model of concentric circles (epicycles) to of concentric circles (epicycles) to demonstrate star and planetary motionsdemonstrate star and planetary motions

He followed a geocentric modelHe followed a geocentric model His Almagest had most of AristotleHis Almagest had most of Aristotle’’s ideas s ideas

in it, with a geocentric approach. in it, with a geocentric approach. Because it survived long periods of Because it survived long periods of

upheaval and wars, and was upheaval and wars, and was ““thethe”” astronomy manual until the time of astronomy manual until the time of Columbus.Columbus.

So, what was known back then….and So, what was known back then….and then lost?then lost?

The earth is roundThe earth is round Circumference/diameter of the Circumference/diameter of the

earth/distance to the moonearth/distance to the moon The solar system is heliocentric.The solar system is heliocentric. An estimate of the distance to the An estimate of the distance to the

sun (while wrong, much further than sun (while wrong, much further than commonly thought)commonly thought)

Precession of the equinoxesPrecession of the equinoxes Length of the year to a high precisionLength of the year to a high precision

The Story does not end here…The Story does not end here…

Most of what was known was lost again after Most of what was known was lost again after this this ““highhigh”” period of astronomy in Greece, period of astronomy in Greece, Turkey and Egypt.Turkey and Egypt.

Romans were not much interested in Romans were not much interested in astronomy or astrology. astronomy or astrology.

Arabs conquered many of these countries Arabs conquered many of these countries starting in the 7starting in the 7thth century, and preserved a century, and preserved a lot of the work done by the ancients, refined lot of the work done by the ancients, refined it, and passed it back to the western world at it, and passed it back to the western world at the end of the Middle Ages..the end of the Middle Ages..

Thus it became the foundation of the work Thus it became the foundation of the work and ideas that became prevalent in the 15and ideas that became prevalent in the 15thth and 16and 16thth centuries. centuries.