Planetary Motion and Kepler's Laws

Kepler’s 1st Law

each planet orbits the sun in a path called an ellipse

ellipse

oval whose shape is determined by the 2 points within the figure

focus

each point on an ellipse

perihelion

orbit is closest to the sun

aphelion

orbit is farthest from the sun

AU (astronomical unit)

average distance between the earth and the sun

152 million km

aphelion of earth’s orbit

147 million km

perihelion of earth’s orbit

149.5 million km

average of aphelion and perihelion, known as 1 au, equal to 93 million miles

Kepler’s 2nd Law

the speed at which planets travel at different points in their orbits

near the sun

“line” connecting planet is short and the planet moves faster

far from the sun

“line” connecting planet is long and the planet moves slower

Kepler’s 3rd Law

the relationship between the average distance of a planet from the sun

orbital period

the time required for the planet to make one revolution around the sun

88 days

Mercury’s orbital period

687 days

Mars’ orbital period

11.9 years

Jupiter’s orbital period