The Origin of Modern Astronomy

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The Origin of Modern Astronomy

• Chapter 4

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Mesopotamian Astronomy

• MESOPOTAMIANS built observatories starting 10000
  years ago
• the ziggurat had seven levels, one for each
  wandering object in the sky
• Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn
• Thus 7 days to the week
• They tracked stars --- groups rising before sun
  at different times of year implied seasonal
  beginnings for harvesting and planting
  (zodiac).
• Divided circles in 360 degrees,
  each degree into 60 minutes and
  each minute into 60 seconds
  -- we still use!
• Left written records in cunieform so we
  understand them better

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Mesopotamian Astronomy and Influence

• By 2000 BC Ur and other Sumerian and Babylonia
  cities had large temples, or ziggurats, usually
  aligned N-S, like most Egyptian pyramids
• Egyptian and Mesopotamian knowledge passed to
  Europe, Asia and Africa

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Sumerians (10,000 B.C.)
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Astronomy impacted ancient civilizations

• The major driving force in ancient astronomy
  studies was Survival.
• When will rainy/dry season come? When should
  crops be planted/ harvested?
• Navigation

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Astronomy impacted ancient civilizations

• Europeans
• Stonehenge is perhaps one of the best known sites
  of ancient astronomical pursuits.

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Special Seasonal Alignments

• Stonehenge (England -- and others) had many
  alignments for predicting, equinoxes and bright
  stars
• Sun Dagger (New Mexico) shows noon on summer
  solstice other effects in winter equinoxes

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Astronomy impacted ancient civilizations

• Native Americans
• The Big Horn Medicine Wheel in Wyoming is similar
  to Stonehenge in design
• It was built by the Plains Indians
• Its spokes align roughly with solstices and
  equinoxes

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Astronomy impacted ancient civilizations

• Mayans
• Outstanding observers of sun, stars, and moon
• Venus was very important to them
• Skilled at calendar making and tracking long time
  intervals
• Only written language and mathematical system in
  North America

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Mayan Ruins
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Mayan City Recreation
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Astronomy impacted ancient civilizations

• Aztecs
• The Aztec Sun Calendar is a large round stone, 12
  feet across weighing in at 24 tons.
• The calendar was three feet thick as well, so it
  was not small by any means.
• Calendar contained 360 days

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Aztecs
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Astronomy impacted ancient civilizations

• Egyptians
• Huge temples and pyramids were built to have a
  certain astronomical orientation.
• The constellation Orion represented Osirus who
  was the god of death, rebirth, and the afterlife.
  
• The Milky Way represented the sky goddess Nut
  giving birth to the sun god Ra.

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Great Pyramids
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Ancient Greek Astronomers (1)

• Unfortunately, there are _No____ written
  documents about the significance of stone and
  bronze age monuments.
• Greeks tried to understand the motions of the sky
  and describe them in terms of ____Mathematical____
  ______(not physical!) models.

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Ancient Greek Astronomers (2)
Models were generally wrong.

1. ______Geocentric_________ Universe Earth at the
   Center of the Universe.
2. ____Perfect___________ Heavens Motions of all
   celestial bodies described by motions involving
   objects of perfect shape, i.e., spheres or
   circles.

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Ancient Greek Astronomers (3)

• Eudoxus (409 356 B.C.) Model of 27 nested
  spheres
• 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. ____Circular___________ Heavens (described by
spheres)

• He expanded Eudoxus Model to use 55 spheres.

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Eratosthenes ( 200 B.C.)Calculation of the
_______________ radius
Angular distance between Syene and Alexandria
70 Linear distance between Syene and Alexandria
5,000 stadia ? Earth Radius 40,000 stadia
(probably 14 too large) better than any
previous radius estimate.
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Contributing Scientists

• Ptolemy
• Around 140 AD, a Greek astronomer named Claudius
  Ptolemaeus (known today as Ptolemy) constructed
  perhaps the best geocentric model of all time.
• Geocentric Earth-Centered universe
• Explained path of 5 planets well
• However, to achieve its explanatory and
  predictive power, the full Ptolemaic model
  required a series of no fewer than 80 circles.

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Prevailing Theory

• Earth was the center
• of the universe

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Contributing Scientists

• Copernicus
• Nicholas Copernicus Rediscovered ancient
  heliocentric (Sun-centered) model.
• Copernicus asserted that Earth spins on its axis
  and, like all other planets, orbits the Sun.
• Explained retrograde motion
• Seasonal changes in sky

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Contributing Scientists

• Copernicus
• The critical realization that Earth is not at the
  center of the universe is now known as the
  Copernican Revoloution.
• Never widely accepted
• Published after death
• On the Revolution of the Celestial Spheres was
  not published until 1543, the year he died.

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The Copernican Revolution
Nicolaus Copernicus (1473 1543) Heliocentric
Universe (Sun in the Center)
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Copernicus new (and correct) explanation for
retrograde motion of the planets
Retrograde (westward) motion of a planet occurs
when the Earth passes the planet.
This made Ptolemys epicycles unnecessary.
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Revised Model
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Contributing Scientists

• Galileo
• Provided much new data to support the ideas of
  Copernicus.
• Revolutionized the way science was done, so much
  so that he is now widely regarded as the father
  of experimental science.

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Contributing Scientists

• Galileo
• Discovered that
• Moons topography mimics Earths.
• Sun contained blemishes call sunspots.
• Discovered moons of Jupiter
• Cycles of Venus

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Telescopic Image (Away from City)
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Original Moon Sketch Galileo
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Major Discoveries of Galileo

• Moons of Jupiter
• (4 Galilean moons)

(What he really saw)

• Rings of Saturn

(What he really saw)
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Major Discoveries of Galileo (2)

• Surface structures on the moon first estimates
  of the height of mountains on the moon

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Major Discoveries of Galileo (4)

• Phases of Venus (including full Venus),
  proving that Venus orbits the sun, not the Earth!

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Major Discoveries of Galileo (3)

• Sun spots (proving that the sun is not perfect!)

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Galileo Galilei (1594 1642)

• Invented the modern view of science Transition
  from a faith-based science to an
  observation-based science.

• Dramatically improved the telescope

• First to make detailed astronomical observations

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Contributing Scientists

• Kepler
• Pure theorist, used mathematical principles to
  predict planetary orbits
• He based his work almost entirely on the
  observations of another scientist
• Devised laws of planetary motion

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Contributing Scientists

• Kepler
• Keplers First Law has to do with the shapes of
  the planetary orbits
• The orbital paths of the planets are elliptical
  (not necessarily circular).
• Two of the most important points of orbit are the
  planets __perihelion_ (its point of closest
  approach to the Sun) and its ____apehelion__
  (greatest distance from the Sun).

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Contributing Scientists

• Kepler
• Keplers Second Law addresses the speed at which
  a planet traverses different parts of its orbit
• An imaginary line connecting the Sun to any
  planet sweeps out equal areas of the ellipse in
  equal intervals of time.

Py2 aAU3
(Py period in years aAU distance in AU)
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Contributing Scientists

• Tycho Brahe
• Tycho Brahe
• Greatest observational astronomer of era.
• Work was the foundation of Keplers calculations
• Supported Heliocentric Model

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Historical Overview
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New Terms
archaeoastronomy eccentric uniform circular
motion geocentric universe parallax retrograde
motion epicycle heliocentric universe paradigm ecc
entricity, e  
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Discussion Questions
1. Historian of science Thomas Kuhn has said that
De Revolutionibus was a revolution-making book
but not a revolutionary book. How was it an
old-fashioned, classical book? 2. Why might
Tycho Brahe have hesitated to hire Kepler? Why do
you suppose he appointed Kepler his scientific
heir? 3. How does the modern controversy over
creationism and evolution reflect two ways of
knowing about the physical world?
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Quiz Questions
1. Why are Stonehenge and The Big Horn Medicine
Wheel thought to be ancient astronomical
observatories? a. Petroglyphs at each site
describe how they were used to make
observations. b. Ancient Greek writings list the
important discoveries made at each of these two
sites. c. Stones at each site aligned with
significant rising and setting positions. d. Both
a and c above. e. All of the above.
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Quiz Questions
2. Plato proposed that all heavenly motion is a.
constantly changing b. circular c. uniform d.
Answers a and b above. e. Answers b and c above.
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Quiz Questions
3. How did Claudius Ptolemaeus account for the
retrograde motion of the planets? a. Planets
slow down, stop, and then reverse their orbital
direction around the Sun. b. Inner planets orbit
the Sun faster and pass outer planets as they
orbit around the Sun. c. Each planet moves on an
epicycle, that in turn moves on a deferent that
circles around Earth. d. The Sun and Moon orbit
Earth, whereas all the other planets orbit the
Sun. e. None of the above.
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Quiz Questions
4. Who accurately determined the size of Earth by
considering Sun angles at Syene and
Alexandria? a. Thales of Miletus (c. 624-547
BC) b. Pythagoras (c. 570-500 BC) c. Eudoxus
(409-356 BC) d. Aristotle (384-322 BC) e.
Eratosthenes (c. 200 BC)
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Quiz Questions
5. One of the first principles of ancient
astronomy is that the heavens beyond _____ are
perfect, and the Earth is corrupt. a. the
atmosphere b. the Sun c. the Moon d. Saturn e.
Pluto
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Quiz Questions
6. Who taught that the Earth is stationary and at
the center of the universe with the Sun, the
Moon, and the planets moving around Earth in
perfect circles? a. Thales of Miletus (c.
624-547 BC) b. Pythagoras (c. 570-500 BC) c.
Eudoxus (409-356 BC) d. Aristotle (384-322 BC) e.
Eratosthenes (c. 200 BC)
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Quiz Questions
7. How did Nicolaus Copernicus account for the
retrograde motion of the planets? a. Planets
slow down, stop, and then reverse their orbital
direction around the Earth. b. Inner planets
orbit the Sun faster and pass outer planets as
they orbit around the Sun. c. Each planet moves
on an epicycle, that in turn moves on a deferent
that circles around Earth. d. The Sun and Moon
orbit Earth, whereas all the other planets orbit
the Sun. e. None of the above.
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Quiz Questions
8. What feature of Aristotle's model of the
universe was included in the model proposed by
Copernicus? a. Earth is stationary and at the
center. b. Mercury and Venus move around the
Sun. c. Mars, Jupiter, and Saturn move around
Earth. d. Uniform circular motion. e. Elliptical
orbits.
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Quiz Questions
9. Why did the model of the universe proposed by
Copernicus gain support soon after its
publication? a. It more accurately predicted
the position of planets. b. It gave a better
explanation for the phases of the Moon. c. It was
a more elegant explanation of retrograde
motion. d. The old system of Ptolemy was never
very popular. e. It displaced Earth from the
center of the universe.
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Quiz Questions
10. When Tycho observed the new star of 1572, he
could detect no parallax. Why did that result
undermine belief in the Ptolemaic system? a.
This star is closer than the Moon, and thus stars
are not all at the same distance. b. This star is
closer than the Moon, and thus smaller than other
stars. c. This star is farther away than the
Moon, and thus the heavens are perfect and
unchanging. d. This star is farther away than the
Moon, and thus the heavens are not perfect and
unchanging. e. This star is planet-like.
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Quiz Questions
11. What was the most important contribution of
Tycho Brahe to modern astronomy? a. The
invention of the optical telescope. b. The
discovery of four moons orbiting Jupiter. c. A
model of the universe that was part Aristotelian
and part Copernican. d. The study of the
Supernova of 1572. e. Twenty years of accurate
measurements of planetary positions.
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Quiz Questions
12. How was Tycho Brahe able to make more
accurate astronomical measurements than had been
made before his time? a. He used a telescope to
magnify the image and spacing of celestial
objects. b. He designed and used large devices to
measure small angles. c. His island observatory
was hundreds of miles offshore, under very dark
skies. d. His observatory was at high elevation
and thus above much of Earth's atmosphere. e. All
of the above.
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Quiz Questions
13. How did Kepler's first law of planetary
motion alter the Copernican system? a. It
changed the perfect circles to ellipses. b. It
added epicycles to the perfect circles. c. It
placed the Sun at one focus of each orbit. d.
Answers a and c above. e. Answers b and c above.
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Quiz Questions
14. Which of the "First Principles of Ancient
Astronomy" did Kepler's laws contradict? a.
Earth is at the center of the universe. b. The
heavens are perfect and Earth is imperfect. c.
All heavenly motion is uniform and circular. d.
Both a and b above. e. Both a and c above.
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Quiz Questions
15. What does Kepler's second law indicate about
the orbital speed of a planet? a. The orbital
speed of each planet is constant. b. A planet
moves at its slowest when it is closest to the
Sun. c. A planet moves at its fastest when it is
closest to the Sun. d. The orbital speed of a
planet varies in no predictable way. e. None of
the above.
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Quiz Questions
16. If the semimajor axis of a planet is 4 AU,
what is its orbital period? a. 4 years. b. 8
years. c. 16 years. d. 64 years. e. It cannot be
determined from the given information.
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Quiz Questions
17. Galileo's discovery of four moons orbiting
Jupiter showed that planetary bodies could move
and carry moons. This supports the model of the
universe presented by a. Aristotle b. Claudius
Ptolemaeus c. Nicolaus Copernicus d. Both a and b
above. e. All of the above.
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Quiz Questions
18. What phases of Venus are predicted by the
Ptolemaic system? a. New and Crescent phases
only. b. Quarter and Gibbous phases only. c.
Gibbous and Full phases only. d. Crescent and
Gibbous phases only. e. New, Crescent, Quarter,
Gibbous, and Full phases.
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Quiz Questions
19. What phases of Venus were observed by
Galileo? a. New and Crescent phases only. b.
Quarter and Gibbous phases only. c. Gibbous and
Full phases only. d. Crescent and Gibbous phases
only. e. New, Crescent, Quarter, Gibbous, and
Full phases.
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Quiz Questions
20. The phases of Venus observed by Galileo
support the model of the universe presented
by a. Aristotle b. Claudius Ptolemaeus c.
Nicolaus Copernicus d. Both a and b above. e. All
of the above.
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Answers
1. c 2. e 3. c 4. e 5. c 6. d 7. b 8. d 9. c 10. d
11. e 12. b 13. d 14. e 15. c 16. b 17. c 18. a 19
. e 20. c