# Solar System Discoveries

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## Solar System Discoveries

Ptolemy - Egyptian Philosopher who developed the idea of a GEOCENTRIC (Earth centred) Universe using planetary observations made by Greek astronomer Hipparchus.

Nicolaus Copernicus - developed the first HELIOCENTRIC (sun centred) model of the universe. At that time = Earth, Moon, Sun, Five Planets and the Fixed Stars

He suggests that the Earth, abd planets orbit the sun unlike previously thought.

Copernicus explained the occasional retrograde movement of Mars, Jupiter and Saturn.  By placing the sun at the centre of the universe he explained this as Earth "overtaking the outer planets on the inside" as it moved faster in its orbit.

Tycho continued the study into the heliocentric model from his observatory until his death in 1601.  Kepler used Tycho's study of Mars to formulate his LAWS OF PLANETARY MOTION.

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## Kepler's Laws

1 - The planets move in elliptical orbit around the Sun

2 - Relates the planet's speed to its distance from the Sun.  States that a planet moves faster at close range to the sun than when further away.

3 - A simplified equation relating to the orbital period of a planet around the Sun in Years (T) and its mean distance from the Sun in Astronomical Units (r).

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## Galileo Galilei

Used the first Telescope (optick tube) to view the sky and make sketches

His discoveries

• the moon was not spherical but contained mountains and craters
• Venus shows phases like the Moon and changes its apparent size on a timescale of weeks
• Four satellites were in orbit around Jupiter: Callisto, Europa, Ganymede and Io

These were strong evidence of the Heliocentric Universe

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## Newton's Law of Gravity

It states that the gravitational force of attraction between two objects is diretly proportional to the product of their masses and inversely proportional to the square of the distance between them.

= INVERSE SQUARE LAW

This backed up Kepler's 2nd and 3rd threories.

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## Discoveries of Uranus, Ceres, Neptune and Pluto

William Herschel discovered Uranus in 1781.

Giuseppe Piazza discovered Ceres in 1801 although it has only recently been upgraded from asteroid to Dwarf Planet

Franz Xaver von Zach, Piazza, Carl Friedrich Gauss, John Couch Adams and Urbain Le Verrier all observed the existence of a probable star beyond Uranus from the "Wobbles" or PERTURBATION of Uranus.

Johann Galle and Heinrich D'Arrest discovered the new planet new Le Verrier's predicted position.  It was called Neptune.

In 1930 Clyde Tombaugh located Pluto photographically after a second wobble was observed affecting the motion of Uranus gravitationally.

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