Which ancient astronomer developed a geocentric model of the universe explaining the observable motions of the planets?

• Aristotle
• Ptolemy
  
• Copernicus
• Newton

Aristotle concluded that Earth was round because ____.

• it always casts a curved shadow during a lunar eclipse
• he sailed around the world
• he calculated Earth’s circumference
• it exhibited retrograde motion

The apparent westward movement of a planet against the background of stars is called ____.

• retrograde motion
• revolution
• rotation
• universal gravitation

The geocentric model of the universe stated that ____.

• Earth revolved around the celestial sphere
• the sun was the center of the universe
• Earth was a “wanderer”
• Earth was the center of the universe

In the Ptolemaic model of the universe, ____.

• Earth was flat
• Earth was the center of the universe
• the sun was the center of the universe
• Earth 

A measure of the total amount of matter an object contains is called ____.

• density
• mass
• volume
• weight

The first early astronomer to propose a sun-centered solar system was ____.

• Galileo
• Newton
• Copernicus
• Brahe

Which scientist discovered that Venus has phases, just like the moon?

• Ptolemy
• Copernicus 
• Kepler
• Galileo

The force that gravity exerts on an object is called ____.

• mass
• weight
• density
• voiume

What is the shape of a planets orbit?

• elliptical
• circular
• irregular
• parabolic