Chapter 3

Question 1

In Ptolemy’s Earth-centered model for the solar system, Venus’s phase is never full as viewed from Earth because it always lies between Earth and the Sun. In reality, as Galileo first recognized, Venus is __________.

Answer 1

full whenever it is on the opposite side of the Sun from Earth, although we cannot see the full Venus because it is close to the Sun in the sky

Question 2

Imagine that Venus is in its full phase today. If we could see it, at what time would the full Venus be highest in the sky?

Answer 2

at noon

Question 3

When would a new Venus be highest in the sky?

Answer 3

at noon

Question 4

When would you expect to see Venus high in the sky at midnight?

Answer 4

never

Question 5

In Ptolemy’s Earth-centered model for the solar system (not shown), Venus always stays close to the Sun in the sky and, because it always stays between Earth and the Sun, its phases range only between new and crescent. The following statements are all true and were all observed by Galileo. Which one provides evidence that Venus orbits the Sun and not Earth?

Answer 5

We sometimes see gibbous (nearly but not quite full) Venus

Question 6

Kepler’s first law states that the orbit of each planet is an ellipse with the Sun at one focus. Which of the following statements describe a characteristic of the solar system that is explained by Kepler’s first law?
Venus orbits the Sun faster than Earth orbits the Sun.
The Sun is located slightly off-center from the middle of each planet’s orbit.
Earth is slightly closer to the Sun on one side of its orbit than on the other side.
All the planets orbit the Sun in nearly the same plane.
Inner planets orbit the Sun at higher speed than outer planets.
Pluto moves faster when it is closer to the Sun than when it is farther from the Sun.

Answer 6

The Sun is located slightly off-center from the middle of each planet’s orbit.
Earth is slightly closer to the Sun on one side of its orbit than on the other side.

Question 7

Kepler’s second law states that as a planet orbits the Sun, it sweeps out equal areas in equal times. Which of the following statements describe a characteristic of the solar system that is explained by Kepler’s second law?
Pluto moves faster when it is closer to the Sun than when it is farther from the Sun.
The Sun is located slightly off-center from the middle of each planet’s orbit.
Venus orbits the Sun faster than Earth orbits the Sun.
Inner planets orbit the Sun at higher speed than outer planets.
All the planets orbit the Sun in nearly the same plane.
Earth is slightly closer to the Sun on one side of its orbit than on the other side.

Answer 7

Pluto moves faster when it is closer to the Sun than when it is farther from the Sun.

Question 8

Kepler’s third law states that a planet’s orbital period, p, is related to its average (semimajor axis) orbital distance, a, according to the mathematical relationship . Which of the following statements describe a characteristic of the solar system that is explained by Kepler’s third law?
The Sun is located slightly off-center from the middle of each planet’s orbit.
All the planets orbit the Sun in nearly the same plane.
Venus orbits the Sun faster than Earth orbits the Sun.
Pluto moves faster when it is closer to the Sun than when it is farther from the Sun.
Earth is slightly closer to the Sun on one side of its orbit than on the other side.
Inner planets orbit the Sun at higher speed than outer planets.

Answer 8

Venus orbits the Sun faster than Earth orbits the Sun.

Inner planets orbit the Sun at higher speed than outer planets.

Question 9

Consider the hypothetical observation “a planet beyond Saturn rises in west, sets in east.” This observation is not consistent with a Sun-centered model, because in this model __________.

Answer 9

the rise and set of all objects depends only on Earth’s rotation

Question 10

We never see a crescent Jupiter from Earth because Jupiter __________.

Answer 10

is farther than Earth from the SUN

Question 11

Earth is located at one _________ of the moon’s orbit

Answer 11

focus

Question 12

According to Kepler’s second law, Jupiter will be travelling most slowly around the sun at _____________.

Answer 12

aphelion

Question 13

Earth orbit in the shape of an ___________ around the sun

Answer 13

ellipse

Question 14

The mathematical form of Kepler’s third law measures the period in years and the _________ in astronomical units (AU).

Answer 14

semimajor axis

Question 15

According to Kepler’s second law, Pluto will be travelling fastest around the sun when at __________.

Answer 15

perihelion

Question 16

The extent to which Mars’ orbit differs from a perfect circle is called its ________.

Answer 16

eccentricity

Question 17

What practical value did astronomy offer to ancient civilizations?

Answer 17

It helped them keep track of time and seasons, and it was used by some cultures for navigation.

Question 18

Scientific thinking is _________.

Answer 18

based on everyday ideas of observation and trial-and-error experiments

Question 19

The names of the seven days of the week are based on _________.

Answer 19

the seven naked-eye objects that appear to move among the constellations

Question 20

The Metonic cycle is

Answer 20

used to keep lunar calendars approximately synchronized with solar calendars.

Question 21

Ptolemy was important in the history of astronomy because he _________.

Answer 21

developed a model of the solar system that made sufficiently accurate predictions of planetary positions to remain in use for many centuries

Question 22

The ancient Greeks get a lot of attention for their contributions to science because _________.

Answer 22

they were the first people known to try to explain nature with models based on reason and mathematics, without resort to the supernatural

Question 23

What do we mean by a geocentric model of the universe?

Answer 23

A model designed to explain what we see in the sky while having the Earth located in the center of the universe.

Question 24

What was the Ptolemaic model?

Answer 24

An Earth-centered model of planetary motion published by Ptolemy

Question 25

The great contribution of Nicholas Copernicus was to _________.

Answer 25

create a detailed model of our solar system with the Sun rather than Earth at the center

Question 26

The great contribution of Tycho Brahe was to _________.

Answer 26

observe planetary positions with sufficient accuracy so that Kepler could later use the data to discover the laws of planetary motion

Question 27

Which of the following was not observed by Galileo?
Phases of Venus.
	 Mountains and valleys on the Moon
	 Stellar parallax
	 Four moons orbiting Jupiter

Answer 27

Stellar paralax

Question 28

Which of the following statements about an ellipse is not true?

 An ellipse with a large eccentricity looks much more elongated (stretched out) than an ellipse with a small eccentricity.
 The semimajor axis of an ellipse is half the length of the longest line that you can draw across an ellipse.
 A circle is considered to be a special type of ellipse.
 The focus of an ellipse is always located precisely at the center of the ellipse.

Answer 28

The focus of an ellipse is always located precisely at the center of the ellipse.

Question 29

Which of the following is not one of, nor a direct consequence of, Kepler’s Laws?
More distant planets orbit the Sun at slower speeds.
A planet or comet in a noncircular orbit travels faster when it is nearer to the Sun and slower when it is farther from the Sun.
As a planet moves around its orbit, it sweeps out equal areas in equal times.
The force of attraction between any two objects decreases with the square of the distance between their centers.
The orbit of each planet about the Sun is an ellipse with the Sun at one focus.

Answer 29

The force of attraction between any two objects decreases with the square of the distance between their centers.

Question 30

Scientific models are used to _________.

Answer 30

make specific predictions that can be tested through observations or experiments

Question 31

In science, a broad idea that has been repeatedly verified so as to give scientists great confidence that it represents reality is called _________.

Answer 31

a theory