Chapter 1 Questions

Question 1

Which of the following is not a general difference between a planet and a star?

Answer 1

All planets are made of rock and all stars are made of gas.

Explanation:
Planets are not necessarily made of rock; they may be rocky, icy, or gaseous in composition.

Question 2

Our solar system consists of _________________.

Answer 2

The Sun and all the objects that orbit it.

Explanation:
The objects orbiting the Sun include the planets and their moons and countless small objects that include rocky asteroids and icy comets.

Question 3

A typical galaxy is a _________.

Answer 3

Collection of a few hundred million to a trillion or more stars, bound together by gravity.

Explanation:
Our own Milky Way Galaxy is relatively large, containing more than 100 billion stars.

Question 4

Which of the following best describes what we mean by the universe?

Answer 4

The sum total of all matter and energy.

Explanation:
In other words, the universe consists of all the galaxies and everything within and between them.

Question 5

What do astronomers mean by the Big Bang?

Answer 5

The event that marked the beginning of the expansion of the universe.

Explanation:
Based on careful study of the current explanation of the universe (and of the cosmic microwave background, which we’ll discuss later in the book), the Big Bang occurred about 14 billion years ago.

Question 6

Based on observations of the universal expansion, the age of the universe is about ___________.

Answer 6

14 billion years

Explanation:
In other words, current evidence suggests that the universe was born in the Big Bang about 14 billion years ago.

Question 7

A television advertisement claiming that a product is light-years ahead of its time does not make sense because _____.

Answer 7

It uses “light-years” to talk about time, but a light-year is a unit of distance.

Question 8

The term observable universe refers to _____.

Answer 8

The portion of the universe that we can see in principle, given the current age of the universe.

Explanation:
The age of the universe limits how far we can see. For example, in a universe that is 14 billion years old, we cannot see objects located 15 billion light0years away, because their light has not yet had time enough to reach us.

Question 9

On a scale in which the distance from Earth to the Sun is about 15 meters, the distance from Earth to the Moon is _____.

Answer 9

Small enough to fit within your hand.

Question 10

On a scale where the Sun is about the size of a grapefruit and the Earth is about 15 meters away, how far away are the nearest stars besides the Sun?

Answer 10

About the distance across the United States

Question 11

The number of stars in the Milky Way Galaxy is approximately _____.

Answer 11

A few hundred billion.

Question 12

An astronomical unit (AU) is _____.

Answer 12

The average distance between Earth and the Sun.

Question 13

What do we mean when we say the universe is expanding?

Answer 13

Average distances between galaxies are increasing with time.

Question 14

What is the ecliptic plane?

Answer 14

The plane of Earth’s orbit around the Sun.

Question 15

How long does it take the Earth to complete one orbit around the Sun?

Answer 15

One year

Question 16

Which of the following has your “cosmic address” in the correct order?

Answer 16

You, Earth, solar system, Milky Way Galaxy, Local Group, Local Supercluster, universe

Question 17

Using the ideas discussed in your textbook, in what sense are we “star stuff”?

Answer 17

Nearly every atom from which we are made was once inside of a star.

Question 18

How are galaxies important to our existence?

Answer 18

Galaxies recycle material from one generation of stars to the next, and without this recycling we could not exist.

Question 19

When we look at an object that is 1,000 light-years away we see it _____.

Answer 19

As it was 1,000 years ago.

Question 20

Suppose we look at two distant galaxies: Galaxy 1 is twice as far away as Galaxy 2. In that case _____.

Answer 20

We are seeing Galaxy 1 as it looked at an earlier time in the history of the universe than Galaxy 2.

Question 21

Suppose we make a scale model of our solar system, with the Sun the size of a grapefruit. Which of the following best describes what the planets would look like?

Answer 21

The planets are much smaller than the Sun. Four planets are within about 20 meters of the Sun, while the rest planets are spread much farther apart.

Question 22

If you could count the stars at a rate of about one per second, how long would it take to count all the stars in the Milky Way Galaxy?

Answer 22

Several thousand years (around 3,000)

Question 23

The total number of stars in the observable universe is about _____.

Answer 23

The same as the number of grains of sand on all the beaches on Earth.

Question 24

Where is our solar system located within the Milky Way Galaxy?

Answer 24

Roughly halfway between the center of the edge of the visible disk of the galaxy.

Question 25

If we imagine the history of the universe compressed into one year, dinosaurs became extinct ______.

Answer 25

Yesterday morning.

Question 26

Relative to the age of the universe, how old is our solar system?

Answer 26

It is about one-third the age of the universe.

Question 27

How do the speeds at which we are moving with Earth’s rotation and orbit compare to the speeds of more familiar objects?

Answer 27

Earth’s rotation carries most people around the axis faster than a commercial jet travels, and Earth’s orbit carries us around the Sun faster than the Space Shuttle orbits the Earth.

Question 28

Why do the patters of the stars in our sky look the same from year to year?

Answer 28

Because the stars in the constellation are so far away.

Question 29

Astronomers infer that the universe is expanding because distant galaxies all appear to _____.

Answer 29

Be moving away from us, with more distant ones moving faster.

Question 30

Which statement about motion in the universe is not true?

Answer 30

The mysterious dark matter is the fastest-moving material in the universe.

Question 31

When did humans learn that the Earth is not the center of the universe?

Answer 31

Within the past 500 years.