Download geocentric-heliocentric models

An Introduction to Astronomy
The Electromagnetic Spectrum and
Greco-Roman Times
The Electromagnetic Spectrum
• http://imagine.gsfc.nasa.gov/docs/science/kn
ow_l1/emspectrum.html
Greco-Roman Times
• Patterns in the night sky
• Are the objects in the sky similar each night?
• What changes over time?
• Use Stellarium to look at the movement of stars,
including the sun, the moon and the planets
Greco-Roman Times
• Myths and stories
– Constellations
– Movement of celestial objects
• The moon and stars consistently move in the same direction across
the night sky (they rise and set)
• Planets sometimes reverse their direction, which is called
retrograde motion
• The Greeks, Romans, and other cultures named the
planets after gods, based on their characteristics. For
example, in Roman mythology Mercury was a swift
messenger; the planet that orbits the sun the fastest is
named after him.
Greco-Roman Times
• The sun, the moon, and five planets--Mercury, Venus, Mars, Jupiter,
and Saturn could be seen with the naked eye. These seven objects
were used by many cultures to name the days of the week. English
uses a blend of Roman and Germanic names:
– Sunday: The sun's day. Sol was the Roman god of the sun.
– Monday: The moon's day. Luna was the Roman goddess of the moon.
– Tuesday: Tiu's day or Mars day. Tiu was the Germanic god of war. Mars
was his Roman equivalent.
– Wednesday: Woden's day or Mercury's day. Woden/Odin is sometimes
described as the supreme Germanic god, but is also associated with
the Roman god Mercury.
– Thursday: Thor's day or Jove's Day. Thor was the Germanic god of
thunder and lightning. Jupiter, or Jove, was the god of the heavens.
– Friday: Freya's day or Venus' day. Freya is considered the Germanic
equivalent of Venus, the Roman goddess of love and beauty.
– Saturday: Saturn's day. Saturn was the Roman god of agriculture and
of time. The Germanic tribes do not appear to have an equivalent.
Greco-Roman Times
• Aristotle’s Geocentric
Model (or Earth-centered
model)
– 384BC – 322 BC
– Dominated thinking for
2000 years
– Earth at the centre of a
giant sphere
– Stars were attached to a
fixed outer sphere
– Sun, moon and known
planets were attached to
inner spheres
Greco-Roman Times
• Aristotle’s Geocentric
Model
– Was able to predict the
movement celestial
bodies that moved in the
same direction around
the Earth
– Did not explain the fact
that some planets were
observed to sometimes
reverse their direction
Greco-Roman Times
• Ptolemy’s geocentric
model
– Modified Aristotle’s
model by giving planets
another level of circular
motion called
“epicycles”
– Successful in describing
the sometimes
retrograde (or
backwards) movement
of planets
– Video
Greco-Roman Times – Journal Entry
• Oral story telling has long been a strong familial
tradition. These stories are often passed down from
generation to generation. You will write a descriptive
journal entry in the voice of a Greek or Roman citizen
who would have lived between 500BC to 200AD. Your
purpose will be to recount a story of the night sky that
would have been passed down by members of your
family. You might choose to write the story of a
constellation, the moon, the sun or a planet. You must
make sure that your story is clearly influenced and
shaped by the geocentric model of the universe and
that it is written using descriptive language that “paints
a picture” for the reader.