Transcript early views of the universe

Early Views of the Universe
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
• 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
Copernicus
• In the early 16th century,
Copernicus began to
question the notion of
the Earth being at the
centre of the universe
• He proposed a
heliocentric model of the
universe
– The sun was at the centre
– The Earth and other
planets revolved around
the sun
– Planets still had “epicycles”
Galileo
• Suspected that Copernicus was correct but felt
that it was important to test theories and to
gather observations to support ideas.
• In 1609, Galileo constructed a telescope that
allowed him to observe the heavens. The
telescope allowed him to make the
observations that supported a heliocentric
model of the universe
• Galileo's telescope video
Galileo’s Observations
1. Venus - size changes as
an object gets closer or
further away from us.
This would not happen if
Venus was revolving
around the Earth in a
circular orbit as
predicted by Aristotle
and Ptolemy
Venus video
2. Phases of the moon
depend on what fraction
of the sunlit hemisphere
can be seen from Earth.
Galileo’s Observations
3. Jupiter
– If there are objects revolving around Jupiter just
like our moon revolves around the Earth, then
this means that other planets also have moons
and suggests that Earth is not at the centre of
the universe and acts in a similar fashion to other
planets.
– Jupiter video