Comprehension Check 4.5, P. 211

Polish astronomer who proposed a sun-centered system, in which the earth and the other planets revolve around the sun

Copernicus

the three laws of planetary motion

First law - Every planet orbits the sun in an ellipse with the sun as one of the foci of the ellipse and an empty point in space as the other. Second law - As a planet moves closer to the sun, it travels faster; and as it moves farther away, it slows down. Third law - There is a relationship between a planet's distance from the sun and the time it takes the planet to complete one orbit.

German astronomer who formulated the three laws of planetary motion

Johannes Kepler

ancient Greek astronomer that is known for his theory of an earth-centered universe

Ptolemy

English scientist who formulated the law of universal gravitation

Sir Isaac Newton

the law of universal gravitation

The strength of the gravitational force between two objects depends on their masses (the amount of matter they contain) and the distance between them.

the distance between the earth and the sun, or 93 million miles

astronomical unit

a symmetrically shaped oval

ellipse

two central points of an ellipse

foci