Astronomy of the Ancient Peoples

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Astronomy of the Ancient Peoples

• Models of the Universe

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What our ancestors saw

• The sky has been used for thousands of years to
  predict things such as
• Time of day
• Day of the year
• Weather (Red sky at night, sailors delight red
  sky in the morning, sailors take warning)
• Position on the Earth
• When tides will be high or low

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Other uses of the sky

• Sailors used the stars to navigate
• Farmers used celestial patterns to determine when
  to plant and harvest their crops
• Political and religious leaders would use the
  information provided by the sky to make important
  decisions
• We still see predictions made from the sky in the
  form of the daily horoscope

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Some events of historical significance

• People of the Roman empire believed that their
  destinies could be foretold by the stars
• Around 2000 B.C.E., the Chinese began making
  astronomical observations
• By 1000 B.C.E., the Babylonians could predict
  when lunar eclipses would occur

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Astronomical myths

• A Hindu myth tells of seven wise men married to
  seven sisters. All lived in the Northern sky
  until 6 of the sisters left their husbands to
  move to another location. They became the
  Pleiades (an example of an asterism)
• The Algonquin, Iroquois and Narragansett tribes
  believed the constellation Ursa Major to be a
  bear running away from hunters

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The geocentric model of the universe

• This is an Earth-centred model of the universe
  first proposed by Aristotle (who used the
  mathematical theories of Pythagoras and Euclid to
  create his idea)
• He thought that the Earth was at the centre of a
  gigantic sphere to which all other celestial
  bodies (I.e. Sun and other planets) were attached
• He placed the stars on the surface of the
  outermost sphere which he called the firmament
  of fixed stars (celestial sphere)
• He arranged all of the other celestial bodies on
  concentric spheres inside the celestial sphere
• This model could explain the dates and times that
  the celestial bodies would rise and set

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Problems with the geocentric model

• Required 55 inner spheres to explain all of the
  different motions seen in the universe
• Could not explain why Mars, Jupiter and Saturn
  appeared to go backwards through space rather
  than forwards

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The heliocentric model of the universe

• This is a Sun-centred model of the universe
  first proposed in the early 1500s by Nicholas
  Copernicus
• He thought that the Sun was fixed at the centre
  of the universe and that the planets travelled in
  orbits around it
• The orbits of the planets were all arranged in
  the same solar plane (an imaginary, flat disc
  extending out from the equator of the sun)

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Additions to the heliocentric model

• Johannes Kepler determined that the orbits of the
  planets are elliptical rather than circular
• Galileo Galilei also found evidence to support
  this model (Venus has phases much like the moon)

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Galileos story

• In October 1632, Galileo was tried by a group of
  Roman Catholics (the predominant religion in
  Italy at that time) because of his views that the
  sun was at the centre of the universe
• As a result, he was called a heretic, was forced
  to recant his beliefs and was exiled (then later
  allowed to return to Florence and was placed
  under house arrest)
• Was finally pardoned by Pope John-Paul II in 1992