Early Astronomy Humans have been fascinated by the sky for all time Constellations have helped people navigate tell stories are the gods that look over humanity Constellations are groupings of stars that form images much like seeing ID: 780907
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Slide1
Ancient Astronomy
How have Humans come to Observe/Revere the heavens, and How Has it affected Humanity?
Slide2Early Astronomy
Humans have been fascinated by the sky for all time.
Constellations have helped people navigate, tell stories, are the gods that look over humanity.
Constellations are groupings of stars that form images, much like seeing
shaps
in clouds
Each culture has different images/histories with constellations
Slide3Constellations
Ursa
Major
“Big Bear”
“Big Dipper”
Not a constellation – called an asterism
Slide4Constellations
There are 88 recognized constellations in Astronomy today
Some are only visible from the Northern Hemisphere, some only visible from the Southern Hemisphere
Some of the more recognizable ones in Northern Hemisphere are…
Ursa
Major
Ursa
MinorOrionCanis Major
Ecliptic/Zodiachttps://in-the-sky.org/data/constellations_map_equ11012.pdf
Slide5Constellations
The constellations rise and fall at specific times on specific days in a yearly pattern
Their “motion” per day is due to the rotation of the Earth
Their “motion” per year is due to the revolution of the Earth about the Sun
Ancient Astronomers would be able to tell people when to plant/harvest crops, based on the where the constellations were located.
Slide6"When great Orion rises, set your slaves
to winnowing Demeter's holy grain
upon the windy, well-worn threshing floor.
Then give your slaves a rest; unyoke your team.
But when Orion and the Dog Star move
into the mid-sky, and Arcturus sees
The rosy-fingered dawn, then Perseus, pluck
The clustered grapes, and bring your harvest home.“Hesiod - Approx. 500 B.C.
Slide7Winter Constellations
http://webhome.phy.duke.edu/~
hsg/134/observation/winter-sky-stars.jpg
http://webhome.phy.duke.edu/~
hsg/134/observation/winter-sky-map-schematic.jpg
Slide8Ecliptic
Collection of 12 constellations along the plane where the Sun and all major objects of the Solar System revolve.
Slide9Astrology
A pseudo-science that attempts to explain human behaviors based on where the sun/planets are in relation to the constellations of the zodiac
There is absolutely NO evidence that the positions of the planets has any bearing on our experiences/life history
The constellations, however, have historical significance and are maintained in modern astronomy.
Slide10Ancient Civilizations
Astronomy is one of the oldest sciences, and has been used by Humans for as long as history as been recorded
There have been several major contributors to Ancient Astronomy
Ancient Greeks
Arab
Indian
Chinese
Native AmericanAncient EuropeanJust to name a few!!!
Slide11Mesoamerican Astronomy
Mayan
400 A.D. Could predict eclipses, recorded positions of planets.
Astronomy was state-sponsored, and played a role in war, marriage, etc.
Their calendar was more accurate than the one the Europeans were using when they were conquered in the 1500’s
“New Year’s Day” was on July 26
th
, An observatory in Edzna, the sun passed directly overhead on this day.Chichén
Itzá - Mayan city in the Yucatan Peninsula
Slide12Chichén
Itzá
El Castillo – “the snake”
https://
www.youtube.com/watch?v=q0kOyGZxKh4
El
Caracol – “The Observatory”Windows in El Caracol line up with positions of Venus in the sky on an 8 year cycle.
Of 29 possible astronomical events (eclipses, equinoxes, solstices, etc..), there are 20 of them found in the structure.
Slide13El Castillo
Slide14El Caracol
Slide15Other Native American Structures
Casa Grande – Arizona
Believed to be an observatory
Some windows are aligned to Sun, Moon at specific times
Built in the 14
th
century AD, was abandoned by the 16
th centuryBuild by the Hohokam
Slide16Aztec Astronomy
Aztec Astronomy was strongly associated with religion and their moral code
Major cities were built based on astronomical observations
The orientations of structures were as well
The center of their beliefs was the Sun
Our Sun was the “fifth” one, the others having been destroyed by other events
The calendar stone --------------
Slide17Incan Astronomy
Religion and Astronomy were closely linked
The Sun and the Moon were both seen as God.
The Inca grouped stars into Constellations
They had both light and dark constellations (only civilization to do this!!!)
The Light constellations were inanimate
The Dark constellations were animate animals
Slide18Incan Astronomy
Example of “Dark” constellations – named after animals
Mach’acuay
– the Serpent
Hanp’atu
– the Toad
Yutu
– the
Tinamou
Urcuchillay – the LlamaAtoq – the Fox
Machu Picchu – Ceremonial Site, Agricultural experimentation and Astronomical Observatory
Slide19Chinese Astronomy
As early as 2,000 B.C. – Were predicting eclipses
Were among the earliest astronomers in the world
Named stars – Created “Mansions” (Constellations)
Had 28 Mansions
Dunhuang
Map – North Polar Region
Slide20Chinese Astonomy
Had records of Halley’s Comet and “guest stars”, which were supernovas
Had extensive records of the supernova that caused the Crab
Nebula (SN 1054)
Worked with Indian Astronomers during the Tang Dynasty (600-900 A.D.) as well as with Arab Astronomers during the Yuan Dynasty (1200-1400 A.D.)
Were open to the idea that the Earth was in motion, but no formal research was undertaken.
Slide21Greek Astonomy
Archaic Greek Astronomy
Literary references to stars and constellations
Bootes
, Orion,
Ursa
Major, Sirius, etc…
Works of Homer and Hesiod – 700-800 B.C.Some cosmic speculationAnaximander – 600 B.C.Cylindrical Earth, suspended – surrounded by fire
Philolaus – 400 B.C.Cosmos with Sun, Moon, Earth, and anti-Earth (Antichthon
) circling an unseen central fireEarly Greeks knew of the planets and their special place in our solar systemOrphism (religion) – 5th century B.C.
Earth is round, has an axis, rotates in a day, climate zones, etc…
Slide22Greek Astronomy
Greek Planets
5 planets or “wanderers” can be seen with the Naked Eye from Earth
Mercury – Hermes (messenger god)
Venus – Aphrodite (goddess of love)
Mars – Ares (god of war)
Jupiter – Zeus (king of the gods)
Saturn – Cronus (father of Zeus)Careful observations are needed to determine the planets and their locations
Early Greeks thought Venus was two different planets (one in the morning, one in the evening)Hesperius (“evening star”) and Phosphorus (“light-bringer”) – Pythagoras realized they were the same star.
Slide23Eudoxan
Astonomy
The Pythagoreans placed astronomy among the 4 mathematical arts
Arithmetic, Geometry, Music and Astronomy
The
Eudoxan
system involved…
A shift from stellar to planetary concernsThe creation of the “two-sphere” modelThe establishment of theories for planetary observations
Slide24Two Sphere Model
Geocentric (Earth centered) model
Two Regions
Spherical Earth – central and motionless
Heavenly realm – centered on Earth, made of multiple rotating spheres of
aether
.
Plato – 8 heavenly spheres carrying the 7 planets and the fixed starsEudoxus – Used concentric spheres, tilting axes, and different periods of revolutions – was able to approximate the celestial appearances.
Unfortunately all his work was lost, so we only have secondary sources
Slide25Two Sphere Model
Callippus
– Added more spheres (up to 34 now!) to better describe the motion
Aristotle – Added “unrolling” spheres between each set to cancel the motions of the outer set, otherwise he believed the motion would be transferred to the inner planets
Had many critical flaws
Could not predict motions exactly
Could not explain why the planets changed apparent speed
Could not explain changes in brightness of planets
Slide26Hellenistic Astonomy
Apollonius of
Perga
introduced two new
mechinisms
Eccentric deferent – the spheres were slightly off-center from Earth
Deferent and Epicycle
Deferent is the circle carrying the planet around the EarthEpicycle is a small circle, which carries the planetThis allowed the model to explain “retrograde” motion, where the planet appears to move backwards against the ecliptic
Hipparchus Was aware of the extraordinary accuracy of the Babylonian Astonomers
Created a simple eccentric model for the Sun (very accurate!)Used a deferent and epicycle for the Moon (very accurate!)Could not make models for the remaining planets.
Slide27Hipparchus
Also created a star catalogue
Observed a nova (new star)
Discovered Precession, the slow motion of the stars over the course of many, many years.
Attributed this to the motion of the stellar sphere (previously thought to be completely motionless)
Precession is real, but has a different mechanism
Slide28Heliocentrism
Aristarchus of Samos
Proposed a heliocentric (sun-centered) cosmos.
Ideas were not well received, only one known follower
Calculated the sizes of the Earth and the Moon, as well as their distances in Earth radii (didn’t know the size of the Earth)
Shortly later – Eratosthenes calculated the size of the Earth, so a value could be plugged in
Hipparchus also calculated the size of the Sun and Moon
Both guys greatly underestimated the distance of the Sun from the Earth. They were fairly close on the Moon though!!
Slide29Slide30Aristarchus
Used shadows and logic to determine that the Moon was closer to the Earth than the Sun.
The Greeks understood that the moon reflected sunlight.
How should that illumination look like from the Earth?
If Moon is further than sun (should be nearly fully lit)
If Moon is much closer than sun (should be ½ lit)
this is what is true!!!
Estimated the moon’s distance at 40 Earth Radii away (actually 60)
Estimated the Moon to be 1/3
rd the size of Earth’s shadow (actually ¼), this is difficult to measure.To get the solar distance, used the phases of the moon. If the sun were close, there would be a difference in time between the 1
st
and 3
rd
quarter moons due to angles.
Estimated the distance to Sun to be 20x that of the Earth-Moon distance (actually 390x) Logic was sound though
Slide31Ptolemaic Astronomy
The Almagest
Introduced the equant, a new mathematical tool.
Gave a comprehensive treatment of astronomy, which is why it’s one of the few surviving works
Placed the planets in the order that survived until it was replace by the Heliocentric and
T
ychonic
systems in the 1600’sMoon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, Fixed StarsGreatly influenced Indian Astronomy
Slide32Indian Astronomy
Astronomy and Hinduism (primary religion of India) are tightly interwoven
Had extensive contact with Greek civilization, so heavily influenced by them
Indian Astronomer Aryabhata described motions of planets and eclipses in 600 A.D.
Proposed a Heliocentric (Sun-centered model) of the solar system. Believed that the moon reflected sunlight, and that the Earth moved.
(ALL OF THESE ARE TRUE!!!)
Unfortunately, many early record have been destroyed and lost due to invasion/climate
Slide33Arab (Islamic) Astronomy
Mostly a continuation of Greek Astronomy
Many of our records of Greek Astronomy are those saved by the Arabic Cultures
Ptolemy’s work was saved in an Arabic translation called al-
Magiste
820 A.D. – Measured the circumference of the Earth to within 4% of it’s true value
850 A.D. – al-
Farghani corrected many errors in Ptolemy’s work.
Improved measurements of the Earth’s orbital tilt and the precession of the Earth’s axisAdvanced the field of Optics, and used it to make better observations of the sky, building observatories
Slide34Arab (Islamic) Astronomy
Invented the Pinhole camera, used to measure stellar positions
However, they created no new cosmological models because pictorial representations of the heavens are forbidden by the Koran
The prefix ‘al-’ means “the” in Arabic, and it influences many of the names in Astronomy and other fields
Algebra, algorithm, Algol,
Alcor
, Aldebaran, etc…
Many Arabic manuscripts have not even been read or even catalogued at this time, so there may be more fascinating discoveries they made that we don’t know about.
Slide35Egyptian Astronomy
By 3000 B.C.E – Egyptian Astronomers had developed
The 365 day calendar
Alignments of the pyramids to the pole star (
Thuban
)
The pole star moves because of Precession – the slow “wobble” of Earth’s axis over a 26,000 year period
Temple of Amun-Re at Karnak was aligned to the rising of the midwinter sun
It no longer is, because of the obliquity of the Earth’s axis (The 23.5 degree tilt is slowly changing over a 41,000 year period)Religious festivals were timed to Astronomical eventsPredicting the flooding of the Nile river.