1. The History of Astronomy
http://www.phys.uu.nl/~vgent/babylon/babybibl_intro.htm
http://mason.gmu.edu/~jmartin6/howe/Images/pythagoras.jpg
http://www.russellcottrell.com/greek/aristarchus.htm
http://www.mesopotamia.co.uk/astronomer/homemain.html
plato.lib.umn.edu/
http://web.hao.ucar.edu/public/education/sp/images/aristotle.html
http://web.hao.ucar.edu/public/education/sp/images/ptolemy.html
http://www.windows.ucar.edu/tour/link=/people/ancient_epoch/hipparchus.html
http://copernicus.atspace.com/
http://www.danskekonger.dk/biografi/andre/brahe.htm/
http://antwrp.gsfc.nasa.gov/apod/ap960831.html
http://www.lucidcafe.com/library/95dec/newton.html
2. History of Astronomy 2
Introduction
Western astronomy divides into 4 periods
1. Prehistoric (before 500 B.C.)
• Cyclical motions of Sun, Moon and stars observed
• Keeping time and determining directions develops
2. Classical (500 B.C. to A.D. 1400)
• Measurements of the heavens
• Geometry and models to explain motions
3. Renaissance (1400 to 1650)
• Accumulation of data lead to better models
• Technology (the telescope) enters picture
4. Modern (1650 to present)
• Physical laws and mathematical techniques
• Technological advances accelerate
3. The Model of the Cosmos
• It’s a natural thing for people to want to
understand the world around them.
• People build models, a (simplified?)
conceptual framework that represents the
real world and operates in a manner
consistent with observations.
• To be successful, a model MUST be able
to do two things…
4. Model Building
• A model must accept and incorporate all
careful, accurate observations. No
observations may be conveniently
discarded, simply because they contradict
the model. [The model must be refined!]
• A model must be able to make accurate
predictions of future events.
5. Models Change
• Take note of how the model of the cosmos
changes as new observations become
available.
• Take note also of the forces which
resisted logical changes: mental inertia,
political censorship and religious dogma.
6. History of Astronomy 6
1. Prehistoric Astronomy
• The basis of prehistoric astronomy:
– Celestial Sphere
– Rising and setting of Sun, Moon, and
stars
– Constellations
– Annual motion of Sun *
– Motion of planets through zodiac
– Phases of the Moon
– Eclipses *
7. Practical Uses
• Ancient Americans were farmers and needed to
know the best time for planting and harvesting.
• With farming came a practical need for a
calendar.
• As civilization developed, deeper meanings were
attached to astronomical phenomenon.
• An overall trend: the more settled a culture
became, the more religious meanings became
attached to the sky.
8. The Roots of Astronomy
• Already in the stone and bronze ages,
human cultures realized the cyclic
nature of motions in the sky.
• Monuments dating back to ~ 3000 B.C.
show alignments with astronomical
significance.
• Those monuments were probably used
as calendars or even to predict eclipses.
9. Ancient Astronomy
In the beginning, there were 3 basic types of
ancient observatories
• Simple markers
• Circles
– Stone, wood, holes, or lines
• Temples or tombs
– Passageways, shafts, windows, or other
openings that would face the rising/setting
moon, sun or important stars
10. What did the observatories
measure?
• Solstices
• Equinoxes
• Changes of
Seasons
13. Stonehenge
• Stonehenge in southern
England is believed to be part of
an astronomical device which
was completed in 2000 B.C.
• A section of its structure called
the “avenue” points towards the
location at which the Sun rises
in the Summer solstice, and
other sight lines created by the
structure point towards the most
northern and southerly risings of
the Moon.
• It was not used to track the
Moons rising and setting points
15. Big Horn Medicine Wheel
• Arrangement of rocks resembling a 28-spoke
wheel in the Big Horn Mountains of Wyoming
• Used as calendar by the Plains Indians from
about 1500 – 1700 CE
• Used as indicator of summer solstice sunrise
and sunset.
• The alignments are controversial as they could
be due to chance
• It was not used to track the Moons rising and
setting points
16. Tomb at Newgrange, Ireland
• The passage tomb was
constructed in such a way that
on the Winter solstice light from
the rising Sun penetrates the
main passage shining into the
inner chamber for just 17
minutes in the year.
• Researchers have also
discovered evidence that
Newgrange may have been
designed in order to allow light
from the Moon to enter the inner
chamber approximately every
nine years when the Moon’s
path crosses the position that
the Winter solstice Sun would
occupy.
17.
18. Caracol (Maya culture, approx. A.D. 1000)
Contained window that were aligned with rising point of Venus over the horizon
19. 2. Classical (500 B.C. to A.D. 1400)
• Measurements of the heavens
• Distance and Size of the Sun and Moon
• The Shape of the Earth
• The Size of the Earth
• The Motion of the Planets
20. Passage of astronomical knowledge
Ancient
Babylon
Ancient
Egypt
Ancient Greece
Ancient Roman Empire
21. • Around 1200-1000 B.C., the
Babylonians studied astrology –
indeed they invented the 12 signs
of the Zodiac that are still used
today. Around the same time, the
Greeks named most of the stars
and constellations in the
northern hemisphere (e.g.
Hercules, Perseus, Cassiopea,
Cygnus). They also named the
"the wandering stars", which we
now know to be planets. The
Greeks named these after their
gods, Mercury, Venus, Mars and
Jupiter.
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23. II. Egyptian
• Temple at Karnak
– Certain alignments correspond to summer
solstice sunset and winter solstice sunrise
• Pyramid of Khufu at Giza
– Shafts from the King's chamber indicate
• location of Polaris 5000 years ago
• Former position of Orion's belt
– The pyramid is also aligned perfectly N-S and
E-W
26. III. Greek Astronomers
• Unfortunately, there are no written
documents about the significance of
stone and bronze age monuments.
• First preserved written documents
about ancient astronomy are from
ancient Greek philosophy.
• Greeks tried to understand the motions
of the sky and describe them in terms
of mathematical (not physical!) models.
28. Ancient Greek Astronomers
A. Eudoxus (409 – 356 B.C.):
Model of 27 nested spheres
B.Aristotle (384 – 322 B.C.),
major authority of philosophy
until the late middle ages:
Universe can be divided in 2
parts:
1. Imperfect, changeable Earth,
2. Perfect Heavens (described
by spheres)
• He expanded Eudoxus’ Model to use 55 spheres.
29. C. Eratosthenes
• Erathoshenes was able to measure the
radius of the earth as early as 200 CE.
• He then calculated the circumference of
the Earth to be 25,000 miles which is very
close to the real circumference of the
Earth.
33. Ptolemy’s Idea of the Universe
Earth is in the
center.
Planets circle
the earth.
Sun orbits the
Earth.
34. Ptolemy’s 2 other accomplishments
• Ptolemy calculated what he believed to be
the size of the cosmos: 20,000 earth radii
or 134,000,000 kilometers (radius).
• Ptolemy wrote the first astronomy
textbook, the Almagest (the “Majestic
Book”).
36. IV. Rome
The Romans most important contribution
to the field of astronomy is the
enforcement of a systematic calendar
that would account for fact that the year
is about ¼ of a day more 365 days. The
astronomers of Julius Caesar
convinced him to create the
Julian Calendar which adds
one day to the calendar every
4 years to account for the time
we had skipped. This is
known as a “leap year”.
39. Nicolas Copernicus (1473-1543)
Proposed a Heliocentric
Universe
Calculated Relative
Distances to Planets
Copernicus published
his ideas in an influential
book De Revolutionibus
Orbium Coelestium
44. Problems with the Copernican Model
• Copernicus’ model was much simpler and more elegant
than the geocentric model, and it could be used, through
geometry, to accurately measure the distances between the
planets and the sun.
• It also explained retrograde motion in a much more natural
way.
• But there were still problems.
» Could not predict planet positions any more
accurately than the model of Ptolemy
» Could not explain lack of parallax motion of
stars
» Conflicted with Aristotelian “common sense”
46. Church resistance
• Through the centuries, the Church had
interpreted several verses of Scripture to
indicate that the Earth was the center of
the universe.
• Ideas that questioned this Church
teaching might lead people to question
other teachings, threatening the Church’s
religious and temporal power.
47. • He made a huge number
of observations of the
stars and planets, all with
the naked eye
– Even without a telescope,
he was very accurate in his
measurements
• He built an observatory
called the Uraniborg
• Also recorded the
appearance of comets
and supernovae
– The Tycho supernova
remnant is still visible
today
Tycho (1546-1601)
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51. Galileo Galilei (1564-1642)
Observed sky with
telescope
Proved Copernicus right!!
Condemned by Church
Designed simple
experiments about gravity
proofing that a heavy and
light object fall at the
same rate.
52. Major Discoveries of Galileo
• Rings of Saturn
(What he really saw)
(What he really saw)
Proofing that Jupiter was more massive then the Earth
• Moons of Jupiter
(4 Galilean moons)
53. Major Discoveries of Galileo
• Surface structures on the moon; first estimates of the
height of mountains on the moon. This suggested
that the moon was not prefect
59. Isaac Newton (1642-1727)
Discovered the Law of Universal
Gravitation
Proved Kepler’s 3 Laws
Newton’s 3 Laws of motion
First Law A body at rest will
remain at rest, unless a force
acts on it
Second Law Force = Mass X
Acceleration
Third Law For every action
there is an equal and opposite
reaction
Invented reflecting telescope,
calculus, & physics
60. • Newton conducted hundreds of
experiments on light and
discovered the origin of the
spectrum created by prisms
• Newton also
invented the
reflecting
telescope
61. Edmund Halley (1656-1752)
•
• Studied Newton’s theories
• Charted southern hemisphere
stars, cataloged @ 341 stars
• Helped Newton publish his book
by providing him with financial
support
• Noticed that Venus’ path could
be seen
• Calculated comet’s orbit
demonstrating that comets have
an elliptical path around the sun
and return to the same point
Halley’s comet returns every 76
years
62. Albert Einstein (1879-1955)
• His parents were originally told
he would amount to nothing
and was considered to be a
failure.
• Won the Noble Prize in 1921
• Theories of Relativity
• Known mainly for his formula
E = mc2
• Time and distance are not
absolute but relative to the
observers frame of reference
• His famous formula relates to
the converting of mass to
energy and energy to mass.
63. Edwin Hubble (1889-1953)
• Influential in modern astronomy
• Observed that the universe is
expanding
• Classified different galaxies and
noted that they were moving away
from each other which gave rise to
Hawking’s Big Bang Theory.
• Proved that other galaxies existed
beyond our galaxy (The Milky
Way)
• Astronomy was not recognized so
he could not win a Noble Prize;
after his death it became
recognized
• Hubble Telescope was named in
his honor.
64. Steven Hawking (1942- )
•
•
•
Laws that govern the
universe
Big Bang Theory (scientific
not the TV show)
Physics of Black holes
65. History of Astronomy
The sphere of the sky surrounds the Earth and is called the “celestial sphere.”
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66. History of Astronomy
The two constellations Leo, (A), and Cygnus, (B), wit figures sketched in to help you visualize
the an mals they represent. (Photo (A) from Roger Ressmeyer, digitally enhanced by Jon Alpert.
Photo (B) courtesy Eugene Lauria.)
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67. History of Astronomy
The Sun hides from our view stars that lie beyond it. As we move around the Sun, those stars
become visible, and the ones previously seen are hidden. Thus the constellations change with the
seasons.
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68. History of Astronomy
The Earth's rotation axis is tilted by 23.5° with respect to its orbit. The direction of the tilt
remains the same as the Earth moves around the Sun. Thus for part of the year the Sun lies
north of the celestial equator, whereas for another part it lies south of the celestial equator.
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69. History of Astronomy
These five diagrams show the Sun's position as the sky changes with the seasons. Although the
Earth moves around the Sun, it looks to us on the Earth as if the Sun moves around us. Notice
that because the Earth's spin axis is tilted, the Sun is north of the celestial equator half of the
year (late March to late September) and south of the celestial equator for the other half of the
year (late September to late March).
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70. History of Astronomy
The direction of the rising and setting Sun changes throughout the year. At the equinoxes the
rising and setting points are due east and west. The sunrise direction shifts slowly northeast
from March to the summer solstice, whereupon it shifts back, reaching due east at the autumn
equinox. The sunrise direction continues moving southeast until the winter solstice. The sunset
point similarly shifts north and south. Sunrise on the summer solstice at Stonehenge. (Courtesy
English Heritage.)
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71. History of Astronomy
(A) The cycle of the phases of the Moon from new to full and back again. (B) The Moon's phases
are caused by our seeing different amounts of its illuminated surface. The pictures in the dark
squares show how the Moon looks to us on Earth.
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72. History of Astronomy
A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Moon's
shadow strikes the Earth. The photo inset shows what the eclipse looks like from Earth. (Photo
courtesy of Dennis di Cicco.)
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73. History of Astronomy
A lunar eclipse occurs when the Earth passes between the Sun and Moon, causing the Earth's
shadow to fall on the Moon. Some sunlight leaks through the Earth's atmosphere casting a deep
reddish light on the Moon. The photo inset shows what the eclipse looks like from Earth. (Photo
courtesy of Dennis di Cicco.)
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74. History of Astronomy
(A) During a lunar eclipse, we see that the Earth's shadow on the Moon is curved. Thus the
Earth must be round. (B) As a traveler moves from north to south on the Earth, the stars that
are visible change. Some disappear below the northern horizon, whereas others, previously
hidden, become visible above the southern horizon. This variation would not occur on a flat
Earth.
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75. History of Astronomy
Eratosthenes's calculation of the circumference of the Earth. The Sun is directly overhead on the
summer solstice at Syene, in southern Egypt. On that same day, Eratosthenes found the Sun to
be 7° from the vertical in Alexandria, in northern Egypt. Eratosthenes deduced that the angle
between two verticals placed in northern and southern Egypt must be 7°.
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76. History of Astronomy
Aristarchus used the size of the Earth's shadow on the Moon during a lunar eclipse to estimate
the relative size of the Earth and Moon.
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78. History of Astronomy
Aristarchus estimated the relative distance of the Sun and Moon by observing the angle A
between the Sun and the Moon when the the Moon is exactly half lit. Angle B must be 90° for the
Moon to be half lit. Knowing the Angle A, he could then set the scale of the triangle and thus the
relative lengths of the sides.
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79. History of Astronomy
Motion of the Earth around the Sun causes stellar parallax. Because the stars are so remote,
this is too small to be seen by the naked eye. Thus the ancient Greeks incorrectly deduced that
the Sun could not be the center of the Solar System.
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80. History of Astronomy
Cutaway view of the geocentric model of the Solar System according to Eudoxus (Some spheres
omitted for clarity.)
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