21st Century Astronomy

Laura Kay, Stacy Palen, Brad Smith

Chapter 1

Why Learn Astronomy? - 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. Virgo Supercluster

Chris Johnson

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Problem 2

A light-year is a unit of distance most comparable to the distance from Earth to the
a. Moon.
b. Sun.
c. outer Solar System.
d. nearest star.
e. nearest galaxy.

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Problem 3

The following astronomical events led to the formation of life on Earth-including you. Place them in order of their occurrence over astronomical time.
a. Stars died and distributed heavy elements into the space between the stars.
b. Hydrogen and helium were made in the Big Bang.
c. Enriched dust and gas gathered into clouds in interstellar space.
d. Stars were born, and they processed light elements into heavier ones.
e. The Sun and planets formed from a cloud of interstellar dust and gas.

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Problem 4

Suppose you set your keys on the table and left the room. When you came back, they were on the ground. Which of the following is most likely to be true, given the application of Occam's razor?
a. Invisible flying elephants carried them to the floor
b. They just walked off by themselves.
c. Someone bumped the table and knocked them off.
d. A violent wind blew them off the table.

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Problem 5

Suppose the cosmological principle did not apply. Then we could say that
a. planets orbit other stars because of gravity.
b. other stars shine by the same process as the Sun.
c. other galaxies have the same chemical elements in them.
d. light travels in a straight line until it hits something.
e. none of the above

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Problem 6

The scientific method is a way of trying to _______________, not prove, ideas; thus, all scientific knowledge is provisional.

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Problem 7

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.

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Problem 8

The fact that scientific revolutions take place means that
a. all the science we know is wrong.
b. the science we know now is more correct than it was in the past.
c. scientists start out lying, and then get caught.
d. you can never really know anything about the universe; it's all relative.
e. the universe keeps changing the rules.

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Problem 9

If we compare Earth's place in the universe with a very distant place, we can say that
a. the laws of physics are different in each place.
b. some laws of physics are different in each place.
c. all the laws of physics are the same in each place.
d. some laws of physics are the same in each place, but we don't know about others.

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Problem 10

_______________ is the language of patterns and of science.

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Problem 11

T/F: A scientific theory can be tested by observations and proven to be true.

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Problem 12

$\mathbf{T} / \mathbf{F}:$ A pattern in nature can reveal an underlying physical law.

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Problem 13

T/F: A theory, in science, is a guess about what might be true.

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Problem 14

$\mathbf{T} / \mathbf{F}:$ Once a theory is proven in science, scientists stop testing it.

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Problem 14

$\mathbf{T} / \mathbf{F}:$ Once a theory is proven in science, scientists stop testing it.

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Problem 15

T/F: Scientific disputes are solved by debate.

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Problem 16

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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Problem 17

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

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Problem 18

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

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Problem 19

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.

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Problem 20

The circumference of Earth is $1 /7$ s 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 1/7 second.
c. neither a nor b
d. both a and b

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Problem 21

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 formed of material that used to be in the Sun.
d. Earth and the other planets will eventually form a star.

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Problem 22

According to the graphs in Figures 1.12 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.

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Problem 23

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.

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Problem 24

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

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Problem 25

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.

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Problem 26

Suppose you lived on imaginary planet Zorg orbiting Alpha Centauri, a nearby star. How would you write your cosmic address?

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Problem 27

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?

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Problem 28

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

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Problem 29

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

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Problem 30

It is said that we are made of stardust. Explain why this statement is true.

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Problem 31

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?

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Problem 32

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

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Problem 33

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

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Problem 34

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

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Problem 35

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

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Problem 36

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?

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Problem 37

Astrology makes testable predictions. For example, it predicts that the horoscope for your star sign on any day should fit you better than do 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?

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Problem 38

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.

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Problem 39

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

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Problem 40

Why was Pluto reclassified as a dwarf planet?

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Problem 41

Convert the following numbers to scientific notation:
a. 7,000,000,000
b. 0.00346
c. 1,238

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Problem 42

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

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Problem 43

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

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Problem 44

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 ?

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Problem 45

The average distance from Earth to the Moon is $384,000 \mathrm{km}$. How many days would it take you, traveling at $800 \mathrm{km} / \mathrm{h}-$ the typical speed of jet aircraft-to reach the Moon?

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Problem 46

(a) If it takes about 8 minutes for light to travel from the Sun to Earth, and Pluto is 40 times farther from Earth than the Sun is, how long does it take light to reach Earth from Pluto?
(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 Pluto?

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Problem 47

Study the Process of Science figure on page $10 .$ Make a similar flowchart for your behavior while sitting at the computer for an hour. It might include, for example: checking Facebook, looking at blogs, working on homework, checking email, looking things up on Wikipedia. Many of these things are done multiple times. Make sure you show this repetition on the flowchart.

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Problem 48

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?

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Problem 49

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?

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Problem 50

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.

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Problem 51

The number of pages in a science journal published every year increased exponentially from 625 pages in 1940 to 14,000 pages in $1980 .$ Sketch two graphs of this increase: one with linear axes, and one with logarithmic axes.

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Problem 52

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

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Problem 53

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.

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Problem 54

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 one day?

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Problem 55

Gasoline is sold by the gallon in the United States and by the liter nearly everywhere else in the world. There are approximately 3.8 liters in a gallon. If the price of gas is $\$ 4$ per gallon, how much does it cost per liter?

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Problem 56

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?

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Problem 57

Go to the Hayden Planetarium website (http://www. haydenplanetarium.org/universe) and view the short video The Known Universe, which takes the viewer on a journey from the Himalayan mountains to the most distant galaxies. Do you think the video is effective for showing the size and scale of the universe?

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Problem 58

A similar film produced in 1996 in IMAX, 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, a 1968 documentary, can be viewed online at http: $/ /$ w w w.powersof10.com/film, but notably it extends only a hundredth as far as the newer ones.)

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Problem 59

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?

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Numerade Educator

Problem 60

Go to a blog about astronomy or space. There are good collections at http://www.scienceblogs.com and http://blogs. discovermagazine.com. 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?

Chris Johnson

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