What celestial object(s) did ancient humans track as early as 40,000 years ago?

• stars
• phases of the moon
• comets
• asteroids

What does the term "geocentric" mean?

• Earth-centered
• Sun-centered
• Star-centered
• Universe-centered

For most of human history, what did we believe about the Earth's position in the universe?

• Earth was a wandering planet
• Earth revolved around the Moon
• Earth was the center of the universe
• Earth was flat

What did Ptolemy introduce to explain the retrograde motion of planets?

• Elliptical orbits
• Epicycles and deferents
• A new model based on gravity
• A perfect sphere

The term planet comes from ancient Greek, and means...

• bright star
• orbiter
• wanderer
• cycle

For how long was Ptolemy's model of celestial motions accepted?

• 500 years
• 1500 years
• 200 years
• 100 years

What does the term "retrograde motion" refer to?

• The apparent motion of the Earth around the Sun
• The apparent backward motion of planets
• The rotation of the Earth
• The movement of stars

What percentage of the solar system's mass does the Sun contain?

• 50%
• 75%
• 99.8%
• 90%

What is the main point the video makes about reference frames?

• They are irrelevant to motion
• They are always fixed
• They can be centered anywhere
• They must always include the Sun

What is suggested as a better model for understanding the solar system?

• The Earth-centered model
• The Sun-centered model
• A random model
• A flat Earth model