Johannes Kepler, a famous 17th century
astronomer, discovered the basic laws of planetary orbits.
His first law states that planets move in ellipses,
with the sun at one focus.
Scientists use the term eccentricity to describe the
shape of an ellipse. (Eccentricity literally means "off
center"—exactly what the sun is compared to Earth's
orbit!) A circular orbit has an eccentricity of zero.
The more stretched out the orbit, the higher its eccentricity.
! Move your cursor over each planet to display the eccentricity
of its orbit. Use the information to answer the question
below.
