Transcript Powers of ten notation

The Copernican revolution
Discussion
What is the simplest universe imaginable: one
where making predictions about the future
would be the easiest thing to do?
Second Simplest Universe
• Stars unchanging and fixed to the celestial
sphere
• Celestial sphere rotates about Earth
moving east to west once a day carrying
the Sun, Moon and planets with it.
Third Simplest Universe
• Sun, Moon, and planets are carried east to
west along with rotation of celestial sphere
• Sun, Moon and planets move more slowly
west to east against celestial sphere each
at a different rate on a sphere of their own
Ptolemy’s explanation for
retrograde motion
• Each planet moves on a small circle called
and epicycle.
• The center of each epicycle moves along a
larger circle centered near the Earth called
a deferent.
Ptolemaic system
• Very successful at predicting positions of
the planets but was not perfect
• Offered no explanation of why the planets
moved on deferents and epicycles
• There was no relationship between period
of revolution and epicycle size
Heliocentric model
Aristarchus – 3rd century BC
Reintroduced by Copernicus in 16th century
Heliocentric model
• Sun at the center
• Diurnal motion explained by rotation of the
Earth
• All the planets including Earth revolve
about the Sun in circular orbits with
different speeds
Advantages of heliocentric
model
• Provides natural explanation of retrograde
motion.
• Provides natural explanation of motion of
Mercury and Venus as inferior planets, i.e.
their orbits are interior to that of the Earth.
• Provided a relationship between distance
from Sun and orbital period.
Discussion
Why do you think the heliocentric model
rejected?
Disadvantages of the heliocentric
model
• Still required epicycles
• Was no better at predicting planetary
positions
• No stellar parallax observed
Tycho Brahe’s Epilepsy Medicine:
The basic substance is the head of a person who
has been hanged or otherwise executed. The
head should be dried and crushed together with
peony seeds to a powder. This medicine should
not be taken at the full moon.
Tycho Brahe showed that the
celestial sphere could change
• Tycho’s supernova of 1572 – showed that
this new star had no parallax and thus was
more distant than the Moon
• Comet of 1577 – showed that it too was
beyond the distance of the Moon
Kepler’s first law of planetary
motion
The orbit of a planet about Sun is an ellipses
with the Sun at one focus.
Kepler’s Second law of planetary
motion
A line drawn from the planet to the Sun
sweeps out equal areas in equal intervals of
time.
Kepler’s third law of planetary
motion
The square of the sidereal period is equal to
the cube of the semimajor axis of the orbit.
Advantages of Kepler’s model
Allowed near perfect ability to predict
planetary positions
Disadvantages of Kepler’s model
No explanation as to why planets moved
according to his three laws
Still no parallax
Galileo
Galileo’s Observations
• The Sun had spots which were considered
imperfections
• The Moon had mountains and valleys
• The Milky Way resolved into countless stars
• Jupiter had four moons that clearly orbited
it and not the Earth
• Venus had phases
Discussion
Why is the discovery of Jupiter’s Moons
important to the Copernican model?
Jupiter acted like a smaller
version of the Solar System
• Jupiter is bigger than its four moons and
the moons orbit it
• Jupiter’s moons orbit with periods that are
longer for those moons that are furthest
from the planet
Discussion
Explain why the observations of the phases
of Venus prove that Venus must orbit the
Sun. Why is this different than the Moon,
which also has phases but orbits the Earth?
Newton
Newton’s Universal Law of
Gravity
• Every mass attracts every other mass
through a force called gravity
• The force is directly proportional to the
product of their masses
• The force is inversely proportional to the
square of the distance between them
M 1M 2
F G
2
d
Argument by analogy
If Earth is a planet orbiting the Sun just like the
other planets, than the other planets are just
like the Earth.
All planets have life and humans living on them.