Download Volcanoes and Igneous Activity Earth - Chapter 4

Kepler’s Laws
EARTH SCIENCE

Early Astronomy
The Birth of Modern Astronomy
 Johannes Kepler
• Kepler discovered three laws of planetary motion:
1. Orbits of the planets are elliptical.
2. Planets revolve around the sun at varying
speed.
3. There is a proportional relationship between
a planet’s orbital period and its distance to
the sun.
22.1 Early Astronomy
The Birth of Modern Astronomy
 Johannes Kepler
• An ellipse is an oval-shaped path.
• An astronomical unit (AU) is the average
distance between Earth and the sun; it is about
150 million kilometers.
Planet Revolution
The Solar System Model Evolves
Gravity’s Influence on Orbits
Note:
• The seasons are NOT caused by the
distance from the sun.
Let’s see some ellipses
Perihelion Jan 3
93,000,000 miles
Aphelion July 4
95,000,000 miles
Not drawn to scale! The shape
is more like a circle
Kepler’s Laws
• 1) All planets travel in elliptical orbits with
the sun at one focus.
• Note: The Earth's orbit is so close to a
perfect circle that it can't be distinguished
with the human eye.
An ellipse: the sun as one foci
• 2) Each planet travels in such a way that a
line joining the planet and the sun sweeps
equal areas in equal times.
April
March
February
May
June
January
July
August
September
December
October
November
• 3) Relationship between
distance and period:
P2 = D3
Where P is the Period in Earth Years
And D is the distance in “AU’s”
An “AU” is an astronomical unit, which is
the average distance from the sun to the
Earth.
Kepler’s Third Law
• In this equation P represents the period of revolution for
a planet and R represents the length of its semi-major
axis.
• Kepler's Third Law implies that the period for a planet to
orbit the Sun increases rapidly with the radius of its
orbit.
• Thus, we find that Mercury, the innermost planet, takes
only 88 days to orbit the Sun but the outermost object
(Pluto) requires 248 years to do the same.
http://www.physics.sjsu.edu/tomley/Kepler12.html