Johannas KeplerJohannas Kepler

Planetary Orbital LawsPlanetary Orbital Laws

Keplerrsquos First LawKeplerrsquos First Law

The orbit of the planets are The orbit of the planets are ellipsesellipses with with the sun at one focus of the ellipsethe sun at one focus of the ellipse

Ellipses and Ellipses and EccentricityEccentricity

The amount of flattening of the ellipse is The amount of flattening of the ellipse is termed the eccentricitytermed the eccentricity

Circle = 0Circle = 0

Straight Line = 1Straight Line = 1

EllipsesEllipses

The The sunsun is not at the center of the ellipse is not at the center of the ellipse

There is nothing at the other focusThere is nothing at the other focus

Keplerrsquos Keplerrsquos Second LawSecond Law

The line joining the planet to the Sun sweeps The line joining the planet to the Sun sweeps out equal out equal areas in equal times as the planet areas in equal times as the planet travels around the ellipsetravels around the ellipse

Good ExampleGood Example

Perihelion = Point closest to Sun (fastest)Perihelion = Point closest to Sun (fastest)

Aphelion = Point farthest from Sun (Slowest)Aphelion = Point farthest from Sun (Slowest)

Astronomical DistancesAstronomical Distances

An Astronomical Unit (AU) is the average An Astronomical Unit (AU) is the average distance between Earth and the Sundistance between Earth and the Sun

Used when measuring distances to other solar Used when measuring distances to other solar system objectssystem objects

A A Light year Light year is the distance it takes light to is the distance it takes light to travel in 1 yeartravel in 1 year

Used to measure distances to other stars and Used to measure distances to other stars and galaxiesgalaxies

Keplerrsquos Keplerrsquos Third LawThird Law

The closer the object is to the Sun the The closer the object is to the Sun the faster its period of revolutionfaster its period of revolution

Example Example

Earth amp Mars OrbitEarth amp Mars Orbit