Earth

Aristotle BC 384-322

Aristotle

Geocentric model

Nicolas Copernicus1473-1543

Eyeball observations

De Revolutionibus

The Earth rotates on its axis once daily and revolves around the Sun once yearly.

Heliocentric Model

Tycho Brahe (1546-1601)

Johann Kepler (1571-1630)

Kepler’s 1st Law “ellipses”

Kepler’s 2nd Law “equal areas in equal times”

 

Planet Period Distance P/D P/D2 P2/D3

Mercury 0.24 0.39 0.62 1.60 0.99

Venus 0.62 0.72 0.85 1.18 1.00

Earth 1.00 1.00 1.00 1.00 1.00

Mars 1.88 1.52 1.23 0.81 1.00

Jupiter 11.9 5.20 2.28 0.44 1.00

Saturn 29.5 9.51 3.10 0.33 1.01

Kepler’s 3rd Law“Harmonic Law”

Astronomical Unit

Average Distance to Sun from the Earth

1 A.U. = 150 million km

Examples:Mercury 0.4 A.U.Neptune 30 A.U.