Hopi sunrise calendar Observed by a Sun priest at Pueblo Used to anticipate ceremonials

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1 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 sunrise calendar Observed by a Sun priest at Pueblo Used to anticipate ceremonials Stonehenge c.a. 2800BC Constructed and reconstructed on Salisbury Plain in England over thousands of years beginning about 2,800 BC Probably used as a calendar and almanac of solar and lunar motion Stones were brought from many miles away showing its importance There are many other similar Neolithic (new stone age) sites throughout Britain S T O N E H E N G E The Great Pyramid c.a. 2600BC Celestial bodies had great significance in Egyptian culture and was integrated into their religion Pyramids are the tombs of Egyptian Pharaohs, who were believed to be divine gods who were connected to the stars The side of the Pyramids were very accurately aligned north-south The passages and shafts within the Pyramids may have been aligned with astronomical bodies (Orion and a Pole Star) The Pole star was called an imperishable star since it never sets and the spirit of the Pharaoh would journey there 1

2 The Great Pyramids Chichén Itzá c.a AD The Great Pyramids of Gaza may have been arranged in the pattern of the constellation of Orion Orion had special significance in ancient Egypt & represented the god Osiris Osiris is the god of birth, death & resurrection By placing such a configuration on the ground, the god was brought to Earth The pyramids were placed along the Nile, which may have represented the Milky Way 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 of the Caracol Venus, as the morning star, was prominent in Mayan religion and represented their most important god Quetzaloatl Chichén Itzá c.a AD North America - Chaco Canyon El Castillo - a Mayan pyramid at Chichén Itzá Widows in the top of pyramid are aligned with sunrises at the solstices There are also alignments (not shown) with the sunset points of the equinoxes step shadow projects onto northern or southern staircase Chaco Canyon was home to the Anasazi People from 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 s light 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 Asian Alignment Sites City of Vijayanagara in India - 14th century Layout of city is aligned N-S & alignments with Pole Star and other Astronomical objects 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 of sunrise and sunset at the solstices and are also aligned with the rising & setting positions of bright stars Located in Gao Cheng Zhen, China, this giant gnomon was 1st built 2000 years ago (Han Dynasty) Light passes through a 40 ft high window - wall s shadow is measured on a large horizontal scale 2

3 C o n s t e l l a t i o n s Constellations C o n s t e l l a t i o n s Patterns Of Stars Reflect the cultures & times of the people who created them Stable Over Human History Constellations 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 Orion the Hunter Orion is a prominent winter constellation Located near the Celestial Equator so it can been seen from either hemisphere Located near the Milky Way 3

4 Orion Greek Mythology Orion, son of Poseidon and a great, fearless hunter His arrogance angered the goddess Hera who sent a scorpion to kill him The Moon god Artemis placed him in the sky far away 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 prominent northern circumpolar constellation Ursa Major contains the Big Dipper asterism Ursa Minor contains the Little Dipper asterism Ursa Major Ursa Minor Big Dipper Ursa Major & Minor Two stars in the front end of the Big Dipper point to Polaris Greco-Roman Mythology Callisto & Zeus were lovers & had a son, Arcas. Hera, Zeus wife, was angry and turned Callisto into a bear. Years later, Arcas was hunting & was about to kill his mother, so Zeus stepped in & threw them both into the sky. Hera still wanted revenge so she made the pair continually circle the sky, never being able to refresh themselves in the River-Ocean that encircle the Earth. 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 prowls around the sky like a bear. Rishi Arab Representation Persian Representation Early Views of the Cosmos Ancient world pictures of the cosmo geocentric - Earth centered finite - had boundary typically a shell of stars closed off the universe Ancient cosmologies paid little attention to celestial motions even if celestial cycles were carefully observed Colored wood cut by French astronomer Flammarion circa 1880 Nut, Egyptian goddess of sky, arched over Geb, god of Earth Babylonians The Babylonians were among the first people known to have kept astronomical 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 Universe Babylonian tablet recording astronomical information circa 550 B.C. 4

5 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 to the 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 Indi a China Early Greeks Ancient Greek astronomers were the first to attempt to explain the workings of the heavens in a careful, systematic way using naked eye observations and models Greeks enjoyed philosophy which to them meant the attempt to understand all things in nature They used their highly developed mathematical skills (geometry & trigonometry) & logic to make remarkable discoveries about their universe Aristotle & A Spherical Earth Painting of Aristotle by Rembrandt Aristotle ( 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 in eclipses the outline is always curved: and since it is the interposition of the Earth that makes the eclipse, the form of this line will be caused by the form of the Earth s surface which is therefore spherical - Aristotle s treatise On the Heavens Aristotle & A Spherical Earth 2 Aristotle learned from travelers that the height of the Pole star above the horizon varies as you travel from 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 was spherical by watching ships leave port and sail 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 ( 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 the Moon 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 relative to 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 complete phase cycle compared these intervals to determine the Moon-Earth - Sun angle 5

6 Aristarchus of Samos ( B.C.) Estimated size of Sun from total Solar Eclipse using relationship between angular diameter, size and distance Eratosthenes (c. 200 B.C.) Eratosthenes estimated the Earth s diameter, and thereby took the relative measurements of Aristarchus and placed them on an absolute scale Aristarchus estimated all these quantities in terms of the Earth s diameter Aristarchus found that the Sun was much bigger & much farther away than the Moon He therefore concluded that the Sun, not the Earth was at the center of the Universe 7.2 stadia = stadia Earth s circumference Hipparchus (c. 150 B.C.) Erected an observatory on Rhodes & built instruments to measure as accurately as possible the direction of objects in sky compiled catalog of stellar coordinates 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 1 st 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 well predictions fit the best & new observations Scientific models are not static but evolve when new & better observations become available Aristotle s Cosmos Geocentric finite size Motion circular uniform Model consisted of 56 spheres Did not fit observations well Aristotle s Cosmos Corruptible Incorruptible First to incorporate physical ideas or concepts of motion 6

7 Natural Motions Earthy material moved toward center of cosmos Fire moved to highest heights Air below Fire Water between Earth & Air Forced Motions motion of objects on Earth require the application of a force, e.g. cart must be pushed in order to move Question In Aristotlean physics, the Earth was stationary & at center of the Universe Imagine you lived at the time of Aristotle. What observations or evidence could you offer to support the idea 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 their point of departure as they are observed to do If Earth moved about the Sun, then one should observe stellar parallax, yet this was not observed Parallax is the apparent shift in the positions of a body or bodies because of the motion of 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 the Sun or a planet traveled around the Earth, with the Earth displaced from the center Explained the variable motion of the Sun & Planets through the ecliptic Hipparchus Epicycle & Deferent Deferent - a large circle, either centered on Earth or offset from Earth (eccentric) Epicycle - smaller circle, centered on the circumference of the deferent Combination of Epicycle & Deferent explained retrograde motion: Planets fixed to the epicycle Planets moved around epicycle which in turn moved around the deferent 7

8 Assignment Reference Reading: Fundamental Astronomy by Karttunen et al - chap 2 Astronomy & Astrophysics by Zeilik and Gregory - on reserve at Science Library - chapter 1, chapter 3, chapter 4-1 & 4-2 The 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 8