21st Century Astronomy

Laura Kay, Stacy Palen, George Blumenthal

Chapter 1

Thinking Like an Astronomer - all with Video Answers

Educators

Chapter Questions

Problem 1

Rank the following in order of increasing size.
a. Local Group
b. Milky Way
c. Solar System
d. universe
e. Sun
f. Earth
g. Laniakea Supercluster
h. Virgo Supercluster

Kayla Day

Kayla Day

Numerade Educator

Problem 2

If an event were to take place on the Sun, how long would it take for the light it generates to reach us?
a. 8 minutes
b. 11 hours
c. 1 second
d. 1 day
e. It would reach us instantaneously.

Kayla Day

Numerade Educator

Problem 3

Understanding in science means that
a. we have accumulated lots of facts.
b. we are able to connect facts through an underlying idea.
c. we are able to predict events on the basis of accumulated facts.
d. we are able to predict events on the basis of an underlying idea.

Chris Johnson

Numerade Educator

Problem 4

The cosmological principle states that
a. on a large scale, the universe is the same everywhere at a given time.
b. the universe is the same at all times.
c. our location is special.
d. all of the above

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Numerade Educator

Problem 5

The Sun is part of
a. the Solar System.
b. the Milky Way Galaxy.
c. the universe.
d. all of the above

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Numerade Educator

Problem 6

A light-year is a measure of
a. distance.
b. time.
c. speed.
d. mass.

Chris Johnson

Numerade Educator

Problem 7

Occam's razor states that
a. the universe is expanding in all directions.
b. the laws of nature are the same everywhere in the universe.
c. if two hypotheses fit the facts equally well, the simpler one is the more likely to apply.
d. patterns in nature are really manifestations of random occurrences.

Chris Johnson

Numerade Educator

Problem 8

The circumference of Earth is $\frac{1}{7}$ of a light-second. Therefore,
a. if you were traveling at the speed of light, you would travel around Earth 7 times in 1 second.
b. light travels a distance equal to Earth's circumference in $\frac{1}{7}$ of a second.
c. neither a nor
d. both a and b

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Numerade Educator

Problem 9

According to the graphs in Figures 1.7 b and c, by how much did the number of viruses increase in four time steps?
a. It doubled.
b. It tripled.
c. It quadrupled.
d. It went up more than 10 times.

Kayla Day

Numerade Educator

Problem 10

Any explanation of a phenomenon that includes a supernatural influence is not scientific because
a. it does not have a hypothesis.
b. it is wrong.
c. people who believe in the supernatural are not credible.
d. science is the study of the natural world.

Chris Johnson

Numerade Educator

Problem 11

"All scientific knowledge is provisional." In this context, provisional means
a. "wrong."
b. "relative."
c. "temporary."
d. "incomplete."

Kayla Day

Numerade Educator

Problem 12

When we observe a star that is 10 light-years away, we are seeing that star
a. as it is today.
b. as it was 10 days ago.
c. as it was 10 years ago.
d. as it was 20 years ago.

Chris Johnson

Numerade Educator

Problem 13

Which of the following was not made in the Big Bang?
a. hydrogen
b. lithium
c. beryllium
d. carbon

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Numerade Educator

Problem 14

"We are stardust" means that
a. Earth exists because of the collision of two stars.
b. the atoms in our bodies have passed through (and in many cases formed in stars.
c. Earth is primarily formed of material that used to be in the Sun.
d. Earth and the other planets will eventually form a star.

Kayla Day

Numerade Educator

Problem 15

The following astronomical events led to the formation of you. Place them in order of their occurrence over astronomical time.
a. Stars die and distribute heavy elements into the space between the stars.
b. Hydrogen and helium are made in the Big Bang.
c. Enriched dust and gas gather into clouds in interstellar space.
d. Stars are born and process light elements into heavier ones.
e. The Sun and planets form from a cloud of interstellar dust and gas.

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Problem 16

Suppose you lived on the planet named "Tau Ceti e" that orbits Tau Ceti, a nearby star in our galaxy. How would you write your cosmic address?

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Problem 17

Imagine yourself living on a planet orbiting a star in a very distant galaxy. What does the cosmological principle tell you about the physical laws at this distant location?

Chris Johnson

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Problem 18

If the Sun suddenly exploded, how soon after the explosion would we know about it?

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Problem 19

If a star exploded in the Andromeda Galaxy, how long would it take that information to reach Earth?

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Problem 20

Give an example of a scientific theory that has been superseded by a newer theory. As scientists developed this new theory, where on the Process of Science Figure did a change occur so that the old theory became invalid and the new theory was accepted?

Kayla Day

Numerade Educator

Problem 21

Some people have proposed the theory that Earth was visited by extraterrestrials (aliens) in the remote past. Can you think of any tests that could support or refute that theory? Is it falsifiable? Would you regard this proposal as science or pseudoscience?

Chris Johnson

Numerade Educator

Problem 22

What does the word falsifiable mean? Give an example of an idea that is not falsifiable. Give an example of an idea that is falsifiable.

Kayla Day

Numerade Educator

Problem 23

Explain how the word theory is used differently in the context of science than in common everyday language.

Chris Johnson

Numerade Educator

Problem 24

What is the difference between a hypothesis and a theory in science?

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Problem 25

Suppose the tabloid newspaper at your local supermarket claimed that children born under a full Moon become better students than children born at other times.
a. Is this theory falsifiable?
b. If so, how could it be tested?

Kayla Day

Numerade Educator

Problem 26

A textbook published in 1945 stated that light takes 800,000 years to reach Earth from the Andromeda Galaxy. In this book, we assert that it takes 2,500,000 years. What does this difference tell you about a scientific "fact" and how our knowledge evolves with time?

Chris Johnson

Numerade Educator

Problem 27

Astrology makes testable predictions. For example, it predicts that the horoscope for your star sign on any day should fit you better than horoscopes for other star signs. Read the daily horoscopes for all of the astrological signs in a newspaper or online. How many of them might fit the day you had yesterday? Repeat the experiment every day for a week and keep a record of which horoscopes fit your day each day. Was your horoscope sign consistently the best description of your experiences?

Kayla Day

Numerade Educator

Problem 28

A scientist on television states that it is a known fact that life does not exist beyond Earth. Would you consider this scientist reputable? Explain your answer.

Chris Johnson

Numerade Educator

Problem 29

Some astrologers use elaborate mathematical formulas and procedures to predict the future. Does this show that astrology is a science? Why or why not?

Chris Johnson

Numerade Educator

Problem 30

Why can it be said that we are made of stardust? Explain why this statement is true.

Kayla Day

Numerade Educator

Problem 31

Review Working It Out 1.1 . Convert the following numbers to scientific notation:
a. 7,000,000,000
b. 0.00346
c. 1,238

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Numerade Educator

Problem 32

Review Working It Out 1.1 . Convert the following numbers to standard notation:
a. $5.34 \times 10^{8}$
b. $4.1 \times 10^{3}$
c. $6.24 \times 10^{-5}$

Kayla Day

Numerade Educator

Problem 33

If a car is traveling at $35 \mathrm{km} / \mathrm{h}$, how far does it travel in
a. 1 hour?
b. half an hour?
c. 1 minute?

Kayla Day

Numerade Educator

Problem 34

Review Appendix 1.7. The surface area of a sphere is proportional to the square of its radius. How many times larger is the surface area if the radius is
a. doubled?
b. tripled?
c. halved (divided by 2 )?
d. divided by 3 ?

Kayla Day

Numerade Educator

Problem 35

The average distance from Earth to the Moon is $384,400 \mathrm{km}$. How many days would it take you, traveling at $800 \mathrm{km} / \mathrm{h}-$ the typical speed of jet aircraft-to reach the Moon?

Kayla Day

Numerade Educator

Problem 36

The average distance from Earth to the Moon is $384,400 \mathrm{km}$. In the late 1960 s, astronauts reached the Moon in about 3 days. How fast (on average) must they have been traveling (in kilometers per hour) to cover this distance in this time? Compare this speed to the speed of a jet aircraft $(800 \mathrm{km} / \mathrm{h})$.

Kayla Day

Numerade Educator

Problem 37

(a) If it takes about 8 minutes for light to travel from the Sun to Earth, and Neptune is 30 times farther from Earth than the Sun is, how long does it take light to reach Earth from Neptune? (b) Radio waves travel at the speed of light. What does this fact imply about the problems you would have if you tried to conduct a two-way conversation between Earth and a spacecraft orbiting Neptune?

Kayla Day

Numerade Educator

Problem 38

The distance from Earth to Mars varies from 56 million km to 400 million $\mathrm{km} .$ How long does it take a radio signal traveling at the speed of light to reach a spacecraft on Mars when Mars is closest and when Mars is farthest away?

Kayla Day

Numerade Educator

Problem 39

The surface area of a sphere is proportional to the square of its radius. The radius of the Moon is only about one-quarter that of Earth. How does the surface area of the Moon compare with that of Earth?

Chris Johnson

Numerade Educator

Problem 40

A remote Web page may sometimes reach your computer by going through a satellite orbiting approximately $3.6 \times 10^{4} \mathrm{km}$ above Earth's surface. What is the minimum delay, in seconds, that the Web page takes to show up on your computer?

Chris Johnson

Numerade Educator

Problem 41

Imagine that you have become a biologist, studying rats in Indonesia. Most of the time, Indonesian rats maintain a constant population. Every half century, however, these rats suddenly begin to multiply exponentially! Then the population crashes back to the constant level. Sketch a graph that shows the rat population over two of these episodes.

Chris Johnson

Numerade Educator

Problem 42

New York is 2,444 miles from Los Angeles. What is that distance in car-hours? In car-days? (Assume a travel speed of $70 \mathrm{mph} .)$

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Numerade Educator

Problem 43

Some theorize that a tray of hot water will freeze more quickly than a tray of cold water when both are placed in a freezer.
a. Does this theory make sense to you?
b. Is the theory falsifiable?
c. Do the experiment yourself. Note the results. Was your intuition borne out?

Chris Johnson

Numerade Educator

Problem 44

A pizzeria offers a 9 -inch-diameter pizza for $\$ 12$ and an 18-inch-diameter pizza for $\$ 24 .$ Are both offerings equally economical? If not, which is the better deal? Explain your reasoning.

Chris Johnson

Numerade Educator

Problem 45

The circumference of a circle is given by $C=2 \pi r,$ where $r$ is the radius of the circle.
a. Calculate the approximate circumference of Earth's orbit around the Sun, assuming that the orbit is a circle with a radius of $1.5 \times 10^{8} \mathrm{km}$.
b. Noting that there are 8,766 hours in a year, how fast, in kilometers per hour, does Earth move in its orbit?
c. How far along in its orbit does Earth move in 1 day?

Kayla Day

Numerade Educator

Problem 46

Go to the interactive "Scale of the Universe" Web page at the Astronomy Picture of the Day website (http://apod.nasa.gov/ apod/apl40112.html). Start at $10^{\circ}$ (human size) and scale upward; clicking on an object gives you its exact size. What astronomical bodies are about the size of the United States? What objects are about the size of Earth? What stars are larger than the distance from Earth to the Sun? How many light-days is the distance of Voyager 1 to the Earth? What objects are about the size of the distance from the Sun to the nearest star? How much larger is the Milky Way than the size of the Solar System? How much larger is the Local Group than the Milky Way? How much larger is the observable universe than the Local Group?

Kayla Day

Numerade Educator

Problem 47

a. For a video representation of the scale of the universe, view the short video The Known Universe at the Hayden Planetarium website (http://www.haydenplanetarium.org/ universe, which takes the viewer on a journey from the Himalayan mountains to the most distant galaxies. How far have broadcast radio programs from Earth traveled? Is the Sun a particularly luminous star compared to others? Do you think the video is effective for showing the size and scale of the universe?
b. A similar film produced in 1996 in IMAX format, cosmic Voyage, can be found online at http://topdocumentaryfilms $.$ com/cosmic-voyage. Watch the "powers of ten" zoom out to the cosmos, starting at the 7 -minute mark, for about 5 minutes. Do the "powers of ten" circles add to your understanding of the size and scale of the universe? (The original film Powers of Ten can be viewed online at http://apod.nasa.gov/apod/ap150324.html, but notably it extends a few powers of ten less than the newer film.)

Kayla Day

Numerade Educator

Problem 48

Go to the Astronomy Picture of the Day (APOD) app or website (http://apod.nasa.gov/apod) and click on "Archive" to look at the recent pictures and videos. Submissions to this website come from all around the world. Pick one and read the explanation. Was the image or video taken from Earth or from space? Is it a combination of several images? Does it show Earth, our Solar System, objects in our Milky Way Galaxy, more distant galaxies, or something else? Is the explanation understandable to someone who has not studied
astronomy? Do you think this website promotes a general interest in astronomy?

Chris Johnson

Numerade Educator

Problem 49

Throughout this book, we will examine how discoveries in astronomy and space are covered in the media. Go to your favorite news website (or to one assigned by your instructor) and find a recent article about astronomy or space. Does this website have a separate section for science? Is the article you selected based on a press release, on interviews with scientists, or on an article in a scientific journal? Use Google News or the equivalent to see how widespread the coverage of this story is. Have many newspapers carried it? Has it been picked up internationally? Has it been discussed in blogs? Do you think this story was interesting enough to be covered?

Chris Johnson

Numerade Educator

Problem 50

Go to a blog about astronomy or space. Is the blogger a scientist, a science writer, a student, or an enthusiastic amateur astronomer? What is the current topic of interest? Is it controversial? Are readers making many comments? Is this blog something you would want to read again?

Kayla Day

Numerade Educator