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Lunar Occultation Transit of Mercury

Early Calendars-Alignments• Many archaeological sites reveal alignments with prominent celestial

events.• Archeoastronomy is the study and interpretation of such alignments.

– The reality of such alignments can be scientifically verified– The cultural significance (e.g. purpose) has been lost to time– However, it is reasonable to assume that at least one purpose was to

predict the seasons, possibly for agriculture, hunting, migration…..

Hopi sunrisecalendar

•Observed by a“Sun priest” atPueblo

•Used to anticipateceremonials

Stonehenge c.a. 2800BC

• Constructed and reconstructed on SalisburyPlain in England over thousands of yearsbeginning about 2,800 BC

• Probably used as a calendar and almanac ofsolar and lunar motion

• Stones were brought from many miles awayshowing its importance

• There are many other similar Neolithic (newstone age) sites throughout Britain

STONEHENGE

The Great Pyramid c.a.2600BC

• Celestial bodies had greatsignificance in Egyptian cultureand was integrated into theirreligion

• Pyramids are the tombs ofEgyptian Pharaohs, who werebelieved to be divine gods whowere connected to the stars

• The side of the Pyramids were very accurately alignednorth-south

•The passages and shafts within the Pyramids may havebeen aligned with astronomical bodies (Orion and a PoleStar)

•The Pole star was called an “imperishable star” since itnever sets and the spirit of the Pharaoh would journey there

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The Great Pyramids• The Great Pyramids of Gaza

may have been arranged in thepattern of the constellation ofOrion

• Orion had special significance inancient Egypt & represented thegod Osiris

• Osiris is the god of birth, death &resurrection

• By placing such a configurationon the ground, the god wasbrought to Earth

• The pyramids were placed alongthe Nile, which may haverepresented the Milky Way

Chichén Itzá c.a. 600-830AD• Chichén Itzá was an important Mayan & Toltec

ceremonial site on the Yucatan• Prominent alignments with Venus & Sun rise &

set were made through windows in the tower ofthe Caracol

Venus, as the morning star, was prominent in Mayan religion and representedtheir most important godQuetzaloatl

Chichén Itzá c.a. 600-830AD

• Widows in the top of pyramid arealigned with sunrises at the solstices

• There are also alignments (notshown) with the sunset points of theequinoxes

– step shadow projects onto northern orsouthern staircase

El Castillo - a Mayan pyramid at Chichén Itzá

North America - ChacoCanyon

• Chaco Canyon was home to the Anasazi People from900 - 1300 A.D.

• Anasazi means “ancient ones” in Navajo• Atop of Fajada Butte, are 3 large stone slabs and a

petroglyph know as the Sun Dagger• The stones are aligned such that at noon on the

solstices & equinoxes, 1 or more daggers of the Sun’slight strike the petroglyph key locations.

Other North American Sites

• Casa Grande in Southern Arizona• A Hohokam pueblo built about 1000 A.D.• Hohokam means “those who have gone”• Windows are aligned with solar and lunar events

• Medicine Wheel in Wyoming• Built by Native Americans of the High Planes

• Rocks laid out in a 90 foot circle

• Radial spokes are aligned with the positions ofsunrise and sunset at the solstices and are alsoaligned with the rising & setting positions ofbright stars

Asian Alignment Sites

• Located in Gao ChengZhen, China, this giantgnomon was 1st built 2000years ago (Han Dynasty)

• Light passes through a 40 fthigh window - wall’s shadowis measured on a largehorizontal scale

• City of Vijayanagara in India - 14th century• Layout of city is aligned N-S & alignments withPole Star and other Astronomical objects

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Constellations

PatternsOfStars

Constellations

StableOver Human History

ConstellationsReflect the cultures &times of the peoplewho created them

The oldest constellations used by astronomers today originated ~ 3000 BC in Mesopotamia

Southern hemisphere constellations used by astronomers originated in the 17th century by sailors

Constellations

Orion the Hunter

• Orion is a prominent winterconstellation

• Located near the Celestial Equator soit can been seen from eitherhemisphere

• Located near the Milky Way

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Orion• Greek Mythology

– Orion, son of Poseidonand a great, fearlesshunter

– His arrogance angeredthe goddess Hera whosent a scorpion to kill him

– The Moon god Artemisplaced him in the sky faraway from Scorpio

• Jewish - the Biblical Samson• Arab - Al Jabbar the giant• China - Hunter and warrior

Tsan• Egypt - The God Osiris• Brazilian - A Cayman “cousin

of the gator”

Ursa Major & Minor

• Ursa Major is the most prominentnorthern circumpolar constellation

• Ursa Major contains the “Big Dipper”asterism

• Ursa Minor contains the “LittleDipper” asterism

Ursa Major

Ursa Minor Big Dipper

Ursa Major &Minor

• Two stars in the front end of theBig Dipper point to Polaris

• Greco-Roman Mythology– Callisto & Zeus were lovers & had a

son, Arcas. Hera, Zeus’ wife, wasangry and turned Callisto into abear. Years later, Arcas washunting & was about to kill hismother, so Zeus stepped in & threwthem both into the sky. Hera stillwanted revenge so she made thepair continually circle the sky, neverbeing able to refresh themselves inthe River-Ocean that encircle theEarth.

Ursa Major• Aztec - Tezcatlipoca- Peg legged god associated

with death & the north• Hindu - the seven Rishi or primordial sages• Chinese - chariot carrying sages• Basques - 2 bullocks followed by 2 thieves,

watched by a herdsman & his 2 servants• Egyptian - ox pulling a man with a hippopotamus

and alligator on his back• Seen as a bear in many cultures despite its long

tail. Perhaps this is due to the notion that it prowlsaround the sky like a bear.

Persian RepresentationArab Representation

Rishi

Early Views of the Cosmos• Ancient world pictures of

the cosmo– geocentric - Earth

centered– finite - had boundary

• typically a shell ofstars closed off theuniverse

• Ancient cosmologies paidlittle attention to celestialmotions even if celestialcycles were carefullyobserved

Nut,Egyptiangoddess ofsky, archedover Geb,god of Earth

Coloredwood cut byFrenchastronomerFlammarioncirca 1880

Babylonians• The Babylonians were among the first

people known to have keptastronomical records– careful observers– kept continuous written records of

observations on clay tablets– observations used for making calendars &

predicting celestial motions

• Babylonian Cosmos:– finite cosmos– no specific shape to Earth– stars attached to a shell far beyond Earth– Sun entered through a gate at edge of

UniverseBabylonian tablet recordingastronomical informationcirca 550 B.C.

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Ancient Views of the Cosmos• Egyptian:

– Earth is flat– Sky is like a flat plate support by 4 mountains– Sun is carried across the sky in a boat from

east to west. At night Sun is carried back tothe east through the Underworld

• India:– Earth is a circular disk surrounded by the

ocean– great mountain in center of world– Sun goes around mountain once a day

• China:– sky is a round dome, surrounding Earth– Earth is square– Sun travels in a big tilted circle

Egypt

India

China

Early Greeks• Ancient Greek astronomers were the first to

attempt to explain the workings of theheavens in a careful, systematic way usingnaked eye observations and models

• Greeks enjoyed philosophy which to themmeant the attempt to understand all things innature

• They used their highly developedmathematical skills (geometry &trigonometry) & logic to make remarkablediscoveries about their universe

Aristotle & A Spherical Earth• Aristotle (384-322 B.C.) showed by proof that

the Earth was spherical:1 He observed that the Earth’s shadow is

curved during a lunar eclipse– “The shapes that the Moon itself shows are of

every kind -straight, gibbous, and concave - but ineclipses the outline is always curved: and since itis the interposition of the Earth that makes theeclipse, the form of this line will be caused by theform of the Earth’s surface which is thereforespherical” - Aristotle’s treatise On the Heavens

Painting ofAristotle byRembrandt

Aristotle & A Spherical Earth2 Aristotle learned from travelers that

the height of the Pole star abovethe horizon varies as you travelfrom North to South• Going North: Polaris gets higher with

respect to the horizon• Going South: Polaris gets lower with

respect to the horizon• Go far enough south -- Polaris no

longer visible

⇒Earth must be spherical!

Flat Earth Spherical Earth

Question

• Aristotle also reasoned that the Earth wasspherical by watching ships leave port andsail off towards the horizon. – What would you observed about a ship sailing

away from you if you lived on a:• Flat Earth ?• Spherical Earth ?

Aristarchus of Samos (310-230 B.C.)• Estimated relative sizes of the Moon &

Earth– timed duration of lunar eclipses– compared the time it takes the Moon to enter

the Earth’s shadow with the time it takes theMoon to cross the Earth’s shadow

• Estimated distance to Moon– measured angular size of Moon & compared

this to the estimate of the Moon’s size relativeto Earth’s diameter

• Estimated distance to Sun– assumed Moon’s orbit was circular & uniform– measured intervals between 1st and 3rd

quarter phases of the Moon & for 1 completephase cycle

– compared these intervals to determine theMoon-Earth - Sun angle

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Aristarchus of Samos (310-230 B.C.)

• Estimated size of Sun– from total Solar Eclipse using

relationship between angulardiameter, size and distance

Aristarchus estimated all these quantities in terms of the Earth’s diameter

⇒ Aristarchus found that the Sun was much bigger & much farther awaythan the Moon⇒ He therefore concluded that the Sun, not the Earth was at the center ofthe Universe

7.20 5000 stadia=

Eratosthenes (c. 200 B.C.)Eratosthenes estimated the Earth’s diameter, and therebytook the relative measurements of Aristarchus and placedthem on an absolute scale

3600 Earth’s circumference7.20 5000 stadia

Hipparchus (c. 150 B.C.)• Erected an observatory on Rhodes & built instruments

to measure as accurately as possible the direction ofobjects in sky

• compiled catalog of stellar coordinates - 850 entries• discovered precession - Earth’s axis of rotation (about

the celestial sphere) continually changes• refined Aristarchus’ technique to measure Moon’s size

& distance– 29.5 Earth diameters (actual distance = 30 Earth

diameters)• determined length of year to within 6 minutes• carefully observed motions of Moon, Sun & planets• predicted lunar eclipses to within 1 hour• 1st to deal with the problem of parallax for solar eclipses

& predicted the paths of totality for solar eclipses• Developed a geometrical, geocentric model of the

Universe

Scientific Models• Conception of a physical model to explain the workings

of nature is a creative act of science• Models apply known laws of nature to explain

observations• Key aspects of a scientific model

⇒ models explain what is seen⇒ models predict observations accurately⇒ simplify your understanding of nature

• Validity of models is tested by checking how wellpredictions fit the best & new observations

• Scientific models are not static but evolve when new &better observations become available

Aristotle’sCosmos

• Geocentric• finite size• Motion

– circular– uniform

• Model consisted of 56spheres

• Did not fit observationswell

• First to incorporatephysical ideas orconcepts of motion

Aristotle’sCosmos

Corruptible

Incorruptible

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Natural MotionsEarthy material moved

toward center of cosmosFire moved to highest heightsAir below FireWater between Earth & Air

Forced Motionsmotion of objects on Earth

require the application of aforce, e.g. cart must bepushed in order to move

Aristotle’ s Physics Question• In Aristotlean physics, the Earth was stationary & at

center of the Universe

• Imagine you lived at the time of Aristotle. Whatobservations or evidence could you offer to support theidea of a stationary Earth?

Aristotle’s Physics• Earth was stationary & at center

of the universe– Natural motion of Earthy material is

toward the center of the cosmos– We do not feel the Earth moving– If Earth rotated then objects thrown

upward would not drop back to theirpoint of departure as they areobserved to do

– If Earth moved about the Sun, thenone should observe stellarparallax, yet this was not observed

Parallax is the apparentshift in the positions ofa body or bodiesbecause of the motionof the observer

Parallax

Hipparchus• Added geometrical devices to the basic Geocentric model of

Aristotle to explain the motions of the planets– Eccentric, Epicycle, Deferent

Eccentric: a circle along which theSun or a planet traveled around theEarth, with the Earth displaced fromthe center

Explained thevariable motion of theSun & Planetsthrough the ecliptic

Hipparchus• Epicycle & Deferent

– Deferent - a large circle, eithercentered on Earth or offsetfrom Earth (eccentric)

– Epicycle - smaller circle,centered on the circumferenceof the deferent

– Combination of Epicycle &Deferent explained retrogrademotion:

• Planets fixed to theepicycle

• Planets moved aroundepicycle which in turnmoved around thedeferent

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AssignmentReference Reading:Fundamental Astronomy by Karttunen et al - chap 2Astronomy & Astrophysics by Zeilik and Gregory - on reserve at

Science Library- chapter 1, chapter 3,

chapter 4-1 & 4-2The Physical Universe, An Introduction to Astronomy by Shu

• Class Project - Due October 23

• Problem Set 1 - Due September 11– Help session for Homework

• Wed Sept. 3, 7 pm Basement Bryant