Chapter 3

Question 1

What is the geocentric model?

Answer 1

A geocentric model is a universe model with Earth at the center and objects orbiting it in perfect circles

Question 2

By observing the sizes of planets over time, astronomers can determine
A. when a planet is moving fastest.
B. that the Earth orbits the Sun.
C. when a planet is close to or far away from Earth.
D. which planets are bigger than other planets.

Answer 2

C. when a planet is close to or far away from Earth.

Question 3

what is a heliocentric model?

Answer 3

proposed by Copernicus, a model where the sun is at the center of the universe and planets orbit it in perfect circles.

Question 4

What are inferior planets?

Answer 4

Inferior planets are closer to the Sun than Earth is. These are
Mercury and Venus.

Question 5

what are superior planets?

Answer 5

Superior planets are farther from the Sun than Earth is. These are
Mars, Jupiter, and Saturn.

Question 6

What is a sidereal period?

Answer 6

A planet’s sidereal period is how long the planet takes to make one
orbit with respect to the stars.

Question 7

what is a synodic period?

Answer 7

A planet’s synodic period is how long the planet takes to return to the
same configuration with the Sun and Earth.

Question 8

When is the best time to observe a superior planet in the sky?
A. at midnight
B. at opposition
C. at conjunction
D. in winter

Answer 8

B. at opposition

Question 9

When is the best time to observe an inferior planet?
A. midnight
B. 6 AM
C. inferior conjunction
D. greatest elongation

Answer 9

D. greatest elongation

Question 10

What is Kepler’s first law?

Answer 10

Ellipses. Planets orbits are ellipses, not circles.

Question 11

what is Kepler’s 2nd law?

Answer 11

Law of equal areas. A planet will go fastest when closest to the sun, and slowest when farthest from the sun.

Question 12

what is Kepler’s 3rd law?

Answer 12

P^2 = A^3 where P is the sidereal period in years and A is the length of the semimajor axis in AU.

Question 13

Which of the following planets has the longest orbital period?
A. Jupiter
B. Mars
C. Saturn
D. Venus

Answer 13

C. Saturn

Question 14

List the planets from closest to farthest from the sun.

Answer 14

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

Question 15

The orbit of the planets is an ellipse with the Sun at
A. the semimajor axis.
B. the center.
C. one focus.
D. the minor axis.

Answer 15

C. one focus.

Question 16

According to Kepler’s second law, where is the planet located when it moves the
fastest?
A. farthest from the star
B. closest to the star
C. located at one of the foci
D. closest to another planet

Answer 16

B. closest to the star

Question 17

If the geocentric model were correct, and Venus orbited the Earth in a circular
orbit, which of the following statements would be true?
A. Venus would have retrograde motion.
B. Venus would not have phases.
C. The apparent size of Venus would not change in the sky.
D. Venus would not have seasons.

Answer 17

C. The apparent size of Venus would not change in the sky.

Question 18

Newtons 1st law of motion is…

Answer 18

the law of inertia: A moving object will stay in constant motion and an object at rest will stay at rest unless acted on by a net force.

Question 19

Newtons 2nd law of motion is…

Answer 19

F=ma

Question 20

Newtons 3rd law of motion is…

Answer 20

For every force, there is an equal and opposite force. (Action/Reaction).

Question 21

Suppose a rocket ship is traveling in interstellar space, and the engine dies.
What will happen to the rocket ship?
A. It will keep moving in a straight line at a constant speed.
B. It will explode.
C. It will slow down and eventually stop moving.
D. It will move into a circular orbit at a constant speed.

Answer 21

A. It will keep moving in a straight line at a constant speed.

Question 22

Maria drops a bowling ball and a pair of socks in a ball off the top of her dorm
building at the same time. What happens?
A. The bowling ball hits the ground first.
B. The socks hit the ground first.
C. Both objects hit the ground at the same time.

Answer 22

C. Both objects hit the ground at the same time.

Question 23

How did the ancients know the planets were different from the stars?

Answer 23

While the stars always remained in the same location, the planets moved
against those stars.

Question 24

The planet Uranus will be observed in retrograde motion when:
A. Uranus is closest to the Sun
B. Uranus is farthest from the Sun
C. Earth overtakes Uranus in its orbit
D. Uranus overtakes Earth in its orbit

Answer 24

C. Earth overtakes Uranus in its orbit

Question 25

Order the following from largest to smallest semimajor axis:
A. a planet with a period of 84 Earth days
B. a planet with a period of 1 Earth year
C. a planet with a period of 2 Earth years
D. a planet with a period of 0.5 Earth years

Answer 25

C. a planet with a period of 2 Earth years
B. a planet with a period of 1 Earth year
D. a planet with a period of 0.5 Earth years
A. a planet with a period of 84 Earth days

Question 26

Which of Galileo’s astronomical observations did Copernicus’s model
explain better than Ptolemy’s?
A. sunspots
B. craters on the Moon
C. the moons of Jupiter
D. the apparent size and phases of Venus

Answer 26

D. the apparent size and phases of Venus