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History of Astronomy. Used as a calendar by locating the position of the sun. Made it easy to predict when to plant or harvest crops. Particularly interested in solstices and equinoxes. Early Astronomers. Stonehenge (2800-1075 B.C.) . Located Salisbury Plain in southern England

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early astronomers

Used as a calendar by locating the position of the sun.

Made it easy to predict when to plant or harvest crops.

Particularly interested in solstices and equinoxes

Early Astronomers
stonehenge 2800 1075 b c
Stonehenge (2800-1075 B.C.)
  • Located Salisbury Plain in southern England
  • Believed to be an ancient calendar used to observe the position of sun and moon.
  • Particular significance is placed on location of sun during winter and spring solstice.
anastasi indians stone slabs 1050 1125 a d

Southwestern USA (Arizona, New Mexico, Utah, Colorado)

  • Credited with the construction of stone slabs that directed beams of sunlight onto a spiral carving on a cliff base.
  • The light would form changing patterns throughout the year and marks the solstices and equinoxes.
  • Also evidence that the used the northern polar stars to navigate during tribal migration.
Anastasi IndiansStone Slabs: (1050 –1125 A.D.)
big horn medicine wheel 1500 1700 a d

An arrangement of rock resembling a 28-spoke wheel in Big Horn Mountains of Wyoming.

  • Used as indicator of summer solstice sunrise and sunset, with other alignments for the rising of certain stars.
  • Approximately 50 similar circles exist in northwestern USA and Canada.
Big Horn Medicine Wheel: (1500 -1700 A.D.)
the greeks
The Greeks:
  • Celestial Sphere: All stars are attached to a sphere that surrounds the Earth. This sphere rotates around the Earth
    • The sun follows a path in the sky around us called the ecliptic.
    • Since the planets move in different paths from the average star. Each planet is given its own separate sphere that moves with the celestial sphere around the Earth.
retrograde motion

  Planets (from the Greek meaning “wanderers” sometimes move faster or slower and occasionally appear to slow to a stop and move backward over a period of days or months.

Retrograde motion of Mars

Retrograde motion
geocentric theory

Planets and sun go around the Earth!

Plato (478-347 B.C.)

  • Taught most perfect form was the circle.
  • Believed all objects in the heavens moved in circular paths.
  • Believed that the heavens were "designed" by God for the measurement of time
Geocentric theory
aristotle 384 322 b c

Earth is round. (Earth’s shadow on moon during a lunar eclipse was curved.)

  • Proposed a geocentric solar system with 55 concentric circular spheres rotating at different velocities around Earth.
Aristotle (384-322 B.C.)
aristarchus 310 230 b c

The Earth rotated on its axis and orbited about the sun!

  • Attempted to determine the size and distances of the sun and moon
  • StellarParallax: As the Earth orbits the Sun, a nearby star appear to shift its position against the background of distant stars.
    • This motion was NOT observed so theory was discredited. (also went against common sense and philosophical beliefs of the time.)
    • Aristarchus claimed parallax occurred but stars were too far away to notice it.
Aristarchus (310-230 B.C.)
claudius ptolemaeus ptolemy c 100 a d

Created a sophisticated mathematical version of geocentric theory to explain motion of the heavens.

  • Used 3 models to explain motion
    • Eccentricity
    • Epicycles
    • Equants
Claudius Ptolemaeus (Ptolemy)(c. 100 A.D.)

Earth is not in the exact center of the universe. Used to provide a scientific explanation of the seasons.


While the sun travels around the Earth in a circular path called the deferent. The planets travel along the deferent on their own circular paths called epicycles.

nicolas copernicus 1473 1543

Distributed an unsigned pamphlet in 1507 outlining his hypothesis of a Heliocentric universe.(Afraid to offend Christian Church)

  • “De RevolutionibusOrbiumCoelestium” published in 1543 outline entire theory. (Realized he was dying)
    • Outlined circular motion of planets around the sun.
    • Explained retrograde as a result Earth and planets as the orbit the sun.
    • Gave relative size of solar system based on Earth’s orbital size (A.U.)
    • Calculated period of motion of planets.
Nicolas Copernicus (1473-1543)
tycho brahe 1546 1601

Most accurate observations and measurement of celestial motion.

  • Published his results in the “Rudolphine Tables” and hired other mathematicians and astronomers to assist him including Johann Kepler.
  • Believed in a geocentric universe.
Tycho Brahe (1546-1601)
johann kepler 1571 1630

First to know quantitatively how solar system worked.

  • Used Brahe’s tables of the positions of the planets to deduce three planetary laws of motion.
  • Embraced the heliocentric theory.
  • Replaced circular orbits with elliptical orbits.
Johann Kepler (1571-1630)
galileo galilei 1564 1642

First scientist to make systematic use of the refracting telescope to look at heavens.

  • Telescopic observations lent support to heliocentric theory.
    • The moon is not smooth. This conflicted with the notion that all heavenly bodies were perfect spheres.
    • Discovery of Jupiter’s moons
    • Observed Venus passing through phases similar to the moon. Proves it orbits around sun not the Earth.
Galileo Galilei (1564-1642)
galileo s legal troubles

Publications of ideas (Concerning the Chief World Systems 1632) gets him interrogated 4 times by Inquisition

  • 1633 was charged with heresy (The Catholic Church condemned heliocentrism as "false and contrary to Scripture").
  • He was forced to recant his views and placed under house arrest until his death.
Galileo’s Legal troubles
isaac newton 1642 1727

Explain why heavenly bodies moved by applying his three law of motion.

  • Determined that for the planets to orbit the sun in elliptical trajectories, they must be subject to a force. (Law of Universal Gravitation)
  • Invented the reflecting telescope
Isaac Newton (1642-1727)