Celestial bodies:A natural object out in space. Includes:

planets cometsmoons starsasteroids

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 Motion1. 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 allcelestial 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 PlanetsMercuryVenusEarthMars

Jovian PlanetsJupiterSaturnUranusNeptune