Johannes Kepler
(1571 – 1630)
• Johannes Kepler was a German mathematician
and astronomer who discovered that the Earth
and planets travel about the sun in elliptical orbits.
He gave three fundamental laws of planetary
motion. He also did important work in optics and
geometry.
Kepler’s Laws
This law describe the orbits of planets
around the Sun.
• Planets move in elliptical orbits with the Sun
as a focus.
• A planet covers the same area of space in the
same amount of time no matter where it is in
its orbit.
• A planet's orbital period is proportional to the
size of its orbit (its semi-major axis).
Kepler's first law is called the Law of Ellipses. It states that
"the path of the planets about the sun is elliptical in shape,
with the center of the sun being located at one focus". An
ellipses includes any circular shape.
• Kepler's Second Law
• It says that a line running from
the sun to the planet sweeps out
equal areas of the ellipse in equal
times. This means that the planet
speeds up as it approaches the sun
and slows down as it departs from
it. Let's use the diagram above to
think through how this is so.
Kepler’s
third Law
• The cube of the mean
distance of a planet from
the sun is directly
proportional to the square
of time it takes to move
around the sun. Kepler's
Third Law implies that the
period for a planet to orbit
the Sun increases rapidly
with the radius of its orbit.