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Celestial bodies:
 A natural object out in space.
 Includes:
planets
comets
moons
stars
asteroids
Stars: give off light and heat
but are very far away. Ex. The
Sun
Planets: moving stars.
 Patterns
made up of stars.
 Celestial bodies move in cyclic
paths called orbits.
 These orbits result from
gravitational forces.
 Planets, suns and moons
revolve on a central axis.
 Stars generally move from east
to west.
 The point around which the
stars rotate is the North Star…
Polaris.
 Ursa Major and Minor, and
Cassiopeia never go below the
horizon.
See pages 360(1)
Aristotle (383-322 B.C.E.)
 Visualized the universe as
being geocentric. This means
the Earth is the centre of the
universe and everything else
revolves around it.
 He believed that the Earth
was a sphere due to the
curved edges observed during
a lunar eclipse.
Ptolemy (83-168 C.E.)
 Based his model on his
observations of Mars.
 Mars orbital path creates a
loop or s-shape in the sky.
 His model showed each planet
attached to a crystal sphere
with its centre at Earth.
 Each planet was not attached
directly to its sphere but to an
off-centre wheel
(epicycle).
 Accepted for
nearly 15oo years.
 Used to locate
and predict the
position of the
Sun, Moon and
stars.
 Along with a compass, it could
be used to describe the
position of any celestial body
in relation to the direction
North and to the horizon.
 Allowed for more accurate
observations to be made.
Copernicus (1473-1543)
 Believed in a heliocentric
universe (Sun at the centre).
 The Earth rotated on its axis
once daily and revolved
around the Sun once a year.
Galileo (1564-1642)
 First person to view the
“heavens” through a
telescope.
 Allowed him to see objects
about 20x closer.
He observed:
 Craters on the
Moon
 Spots on the Sun
 Four “stars” orbiting Jupiter
(called the Galilean Moons)
Now that the Sun was placed at
the centre of our solar system,
other astronomers could work
to understand the motion of
the planets.
Improvements in the telescope
would show new and strange
objects never imagined!
Johannes Kepler (1571-1630)
 Developed 3 Laws of
Planetary Motion
1. All planets move in ellipses
with the Sun at one focus.
2.Planets sweep out at equal
areas of their elliptical orbit
in equal times.
3. The time a planet takes to
revolve around the Sun is
directly related to how far
away it is from the Sun.
Sir Isaac Newton (1643-1727)
 Developed the three laws of
motion.
 First to show that the force of
gravity affects all
celestial bodies,
causing them to
stay in orbit.
 Invented the reflecting
telescope which uses a curved
mirror to focus the light to a
point at an eyepiece.
Inner Planets
 Mercury
 Venus
 Earth
 Mars
Jovian Planets
 Jupiter
 Saturn
 Uranus
 Neptune