The Cosmic Perspective

Jeffrey Bennett, Megan Donahue, Nicholas Schneider

Chapter 2

Discovering the Universe for Yourself - all with Video Answers

Educators

Chapter Questions

Problem 1

What are constellations? How did they get their names?

Narayan Hari

Narayan Hari

Numerade Educator

Problem 2

Suppose you were making a model of the celestial sphere with a ball. Briefly describe all the things you would need to mark on your celestial sphere.

James Kiss

Numerade Educator

Problem 3

On a clear, dark night, the sky may appear to be "full" of stars. Does this appearance accurately reflect the way stars are distributed in space? Explain.

Matt Braby

Numerade Educator

Problem 4

Why does the local sky look like a dome? Define horizon, zenith, and meridian. How do we describe the location of an object in the local sky?

VS

Vivek Singh

Numerade Educator

Problem 5

Explain why we can measure only angular sizes and angular distances for objects in the sky. What are arcminutes and arcseconds?

Matthew Miranda

Matthew Miranda

Numerade Educator

Problem 6

What are circumpolar stars? Are more stars circumpolar at the North Pole or in the United States? Explain.

Mayukh Banik

Numerade Educator

Problem 7

What are latitude and longitude? Does the sky vary with latitude? Does it vary with longitude? Explain.

Rodger Claar

Numerade Educator

Problem 8

What is the zodiac, and why do we see different parts of it at different times of year?

Chris Johnson

Numerade Educator

Problem 9

Suppose Earth's axis had no tilt. Would we still have seasons? Why or why not?

VS

Vivek Singh

Numerade Educator

Problem 10

Briefly describe key facts about the solstices and equinoxes.

Farhanul Hasan

Numerade Educator

Problem 11

What is precession? How does it affect what we see in our sky?

Morgan Thompson

Morgan Thompson

Numerade Educator

Problem 12

Briefly describe the Moon's cycle of phases. Can you ever see a full moon at noon? Explain.

Prabhu Ramji

Numerade Educator

Problem 13

Why do we always see the same face of the Moon?

Zachary Warner

Numerade Educator

Problem 14

Why don't we see an eclipse at every new and full moon? Describe the conditions needed for a solar or lunar eclipse.

Zachary Warner

Numerade Educator

Problem 15

What do we mean by the apparent retrograde motion of the planets? Why was this motion difficult for ancient astronomers to explain? How do we explain it today?

Mayukh Banik

Numerade Educator

Problem 16

What is stellar parallax? How did an inability to detect it support the ancient belief in an Earth-centered universe?

Matthew Miranda

Matthew Miranda

Numerade Educator

Problem 17

The constellation Orion didn't exist when my grandfather was a child.

Mayukh Banik

Numerade Educator

Problem 18

When I looked into the dark lanes of the Milky Way with my binoculars, I saw a cluster of distant galaxies.

Matthew Miranda

Matthew Miranda

Numerade Educator

Problem 19

Last night the Moon was so big that it stretched for a mile across the sky.

Chris Johnson

Numerade Educator

Problem 20

I live in the United States, and during a trip to Argentina I saw many constellations that I'd never seen before.

Chris Johnson

Numerade Educator

Problem 21

live in the United States, and during a trip to Argentina saw many constellations that I'd never seen before.

Chris Johnson

Numerade Educator

Problem 22

Last night I saw Mars move westward through the sky in its apparent retrograde motion.

Mayukh Banik

Numerade Educator

Problem 23

Although all the known stars rise in the east and set in the west, we might someday discover a star that will rise in the west and set in the east.

Chris Johnson

Numerade Educator

Problem 24

If Earth's orbit were a perfect circle, we would not have
seasons.

Tyler Moulton

Numerade Educator

Problem 25

Because of precession, someday it will be summer everywhere on Earth at the same time.

Aja S

Numerade Educator

Problem 26

This morning I saw the full moon setting at about the same time the Sun was rising.

Prabhu Ramji

Numerade Educator

Problem 27

Two stars that are in the same constellation (a) must both be part of the same cluster of stars in space. (b) must both have been discovered at about the same time. (c) may actually be very far away from each other.

Chris Johnson

Numerade Educator

Problem 28

The north celestial pole is $35^{\circ}$ above your northern horizon. This tells you that you are at (a) latitude $35^{\circ} \mathrm{N}$. (b) longitude $35^{\circ} \mathrm{E}$. (c) latitude $35^{\circ} \mathrm{S}$

Mayukh Banik

Numerade Educator

Problem 29

Beijing and Philadelphia have about the same latitude but different longitudes. Therefore, tonight's night sky in these two places will (a) look about the same. (b) have completely different sets of constellations. (c) have partially different sets of constellations.

Chris Johnson

Numerade Educator

Problem 30

In winter, Earth's axis points toward the star Polaris. In spring, the axis points toward (a) Polaris. (b) Vega. (c) the Sun.

Charles Machakwa

Charles Machakwa

Numerade Educator

Problem 31

If the Sun rises precisely due east, (a) you must be located at Earth's equator. (b) it must be the day of either the March or the September equinox. (c) it must be the day of the June solstice.

Charles Machakwa

Charles Machakwa

Numerade Educator

Problem 32

If the Sun rises precisely due east, (a) you must be located at Earth's equator. (b) it must be the day of either the March or the September equinox. (c) it must be the day of the June solstice.

Charles Machakwa

Charles Machakwa

Numerade Educator

Problem 33

A week after full moon, the Moon's phase is (a) first quarter. (b) third quarter. (c) new.

Chris Johnson

Numerade Educator

Problem 34

The fact that we always see the same face of the Moon tells us that the Moon (a) does not rotate. (b) rotates with the same period that it orbits Earth. (c) looks the same on both sides.

Zachary Warner

Numerade Educator

Problem 35

If there is going to be a total lunar eclipse tonight, then you know that (a) the Moon's phase is full. (b) the Moon's phase is new. (c) the Moon is unusually close to Earth.

Chris Johnson

Numerade Educator

Problem 36

When we see Saturn going through a period of apparent retrograde motion, it means (a) Saturn is temporarily moving backward in its orbit of the Sun. (b) Earth is passing Saturn in its orbit, with both planets on the same side of the Sun. (c) Saturn and Earth must be on opposite sides of the Sun.

Eve Rafferty

Numerade Educator

Problem 37

Earth-Centered or Sun-Centered? Decide whether each of the following phenomena is consistent or inconsistent with a belief in an Earth-centered system. If consistent, describe how. If inconsistent, explain why, and also explain why the inconsistency did not immediately lead people to abandon the Earth-centered model.
a. The daily paths of stars through the sky b. Seasons
c. Phases of the Moon d. Eclipses
e. Apparent retrograde motion of the planets

Chris Johnson

Numerade Educator

Problem 38

Shadow Phases. Many people incorrectly guess that the phases of the Moon are caused by Earth's shadow falling on the Moon. How would you convince a friend that the phases of the Moon have nothing to do with Earth's shadow? Describe the observations you would use to show that Earth's shadow can't be the cause of phases.

Chris Johnson

Numerade Educator

Problem 39

Lunar Phases and Time of Day. Roles: Scribe (takes notes on the group's activities), Proposer (proposes explanations to the group), Skeptic (points out weaknesses in proposed explanations), Moderator (leads group discussion and makes sure everyone contributes). Activity: The diagram below represents the Moon's orbit as seen from above Earth's North Pole (not to scale). Each group member should draw a copy of the diagram and label it as you work together on the following questions. a. How would the Moon appear from Earth at each of the eight Moon positions? Label each one with the corresponding phase. b. What time of day corresponds to each of the four tick marks on Earth? Label each tick mark accordingly.
c. Why doesn't the Moon's phase change during the course of one night? Explain your reasoning.
d. At what times of day would a full moon be visible to someone standing on Earth? Write down when a full moon rises and explain why it appears to rise at that time. e. At what times of day would a third-quarter moon be visible to someone standing on Earth? Write down when a third-quarter moon sets and explain why it appears to set at that time. f. At what times of day would a waxing crescent moon be visible to someone standing on Earth? Write down when a waxing crescent moon rises and explain why it appears to rise at that time.

Heather Zimmers

Heather Zimmers

Numerade Educator

Problem 40

New Planet. A planet in another solar system has a circular orbit and an axis tilt of $35^{\circ} .$ Would you expect this planet to have seasons? If so, would you expect them to be more extreme than the seasons on Earth? If not, why not?

Rodger Claar

Numerade Educator

Problem 41

Your View of the Sky.
a. What are your latitude and longitude? b. Where does the north (or south) celestial pole appear in your sky? c. Is Polaris a circumpolar star in your sky? Explain.

Mayukh Banik

Numerade Educator

Problem 42

View from the Moon. Assume you live on the Moon, near the center of the face that looks toward Earth.
a. Suppose you see a full earth in your sky. What phase of the Moon would people on Earth see? Explain. b. Suppose people on Earth see a full moon. What phase would you see for Earth? Explain. c. Suppose people on Earth see a waxing gibbous moon. What phase would you see for Earth? Explain. d. Suppose people on Earth are viewing a total lunar eclipse. What would you see from your home on the Moon? Explain.

Chris Johnson

Numerade Educator

Problem 43

View from the Sun. Suppose you lived on the Sun (and could ignore the heat). Would you still see the Moon go through phases as it orbits Earth? Why or why not?

Eduard Sanchez

Numerade Educator

Problem 44

A Farther Moon. Suppose the distance to the Moon were twice its actual value. Would it still be possible to have a total solar eclipse? Why or why not?

Averell Hause

Carnegie Mellon University

Problem 45

A smaller Earth. Suppose Earth were smaller. Would solar eclipses be any different? If $s 0,$ how? What about lunar eclipses?

Vidhi Bhatt

Numerade Educator

Problem 46

Observing Planetary Motion. Find out which planets are currently visible in your evening sky. At least once a week, observe the planets and draw a diagram showing the position of each visible planet relative to stars in a zodiac constellation. From week to week, note how the planets are moving relative to the stars. Can you see any of the apparently wandering features of planetary motion? Explain.

Donald Albin

Numerade Educator

Problem 47

A Connecticut Yankee. Find the book $A$ Connecticut Yankee in King Arthur's Court by Mark Twain. Read the portion that deals with the Connecticut Yankee's prediction of an eclipse. In a one- to two-page essay, summarize the episode and explain how it helped the Connecticut Yankee gain power.

Shivani Sharma

Numerade Educator

Problem 48

Arcminutes and Arcseconds. There are $360^{\circ}$ in a full circle.
a. How many arcminutes are in a full circle? b. How many arcseconds are in a full circle? c. The Moon's angular size is about $\frac{1}{2}$ What is this in arcminutes? In arcseconds?

Zhuxi Luo

Numerade Educator

Problem 49

Latitude Distance. Earth's radius is approximately $6370 \mathrm{km}$
a. What is Earth's circumference? b. What distance is
represented by each degree of latitude? c. What distance is represented by each arcminute of latitude? similar answers for the distances represented by a degree or arcminute of longitude? Why or why not?

Gregory Higby

Numerade Educator

Problem 50

Angular Conversions I. The following angles are given in degrees and fractions of degrees. Rewrite them in degrees, arcminutes, and arcseconds.
a. $24.3^{\circ}$ b. $1.59^{\circ}$ c. $0.1^{\circ}$ d. $0.01^{\circ}$ e. $0.001^{\circ}$

Wendi Zhao

Numerade Educator

Problem 51

Angular Conversions II. The following angles are given in degrees, arcminutes, and arcseconds. Rewrite them in degrees and fractions of degrees.
a. $7^{\circ} 38^{\prime} 42^{\prime \prime}$ b. $12^{\prime} 54^{\prime \prime}$ c. $1^{\circ} 59^{\prime} 59^{\prime \prime}$ d. $1^{\prime}$ e. $1^{\prime \prime}$

James Kiss

Numerade Educator

Problem 52

Angular size of Your Finger. Measure the width of your index finger and the length of your arm. Based on your measurements, calculate the angular width of your index finger at arm's length. Does your result agree with the approximations shown in Figure $2.7 \mathrm{c}$ ? Explain.

Eric Mockensturm

Eric Mockensturm

Numerade Educator

Problem 53

Find the Sun's Diameter. The Sun has an angular diameter of about $0.5^{\circ}$ and an average distance of about 150 million km. What is the Sun's approximate physical diameter? Compare your answer to the actual value of $1,390,000 \mathrm{km}$

Willis James

Numerade Educator

Problem 54

Find a Star's Diameter. Estimate the diameter of the supergiant star Betelgeuse, using its angular diameter of about 0.05 arcsecond and distance of about 600 light-years. Compare your answer to the size of our Sun and the EarthSun distance.

Ajay Singhal

Numerade Educator

Problem 55

Eclipse Conditions. The Moon's precise equatorial diameter is $3476 \mathrm{km},$ and its orbital distance from Earth varies between 356,400 and $406,700 \mathrm{km} .$ The Sun's diameter is $1,390,000 \mathrm{km},$ and its distance from Earth ranges between 147.5 and 152.6 million $\mathrm{km}$
a. Find the Moon's angular size at its minimum and maximum distances from Earth. b. Find the Sun's angular size at its minimum and maximum distances from Earth. c. Based on your answers to parts a and b, is it possible to have a total solar eclipse when the Moon and Sun are both at their maximum distance? Explain.

Cyra Jelle Calleja

Cyra Jelle Calleja

Numerade Educator

Problem 56

Earth-Centered Language. Many common phrases reflect the ancient Earth-centered view of our universe. For example, the phrase "the Sun rises each day" implies that the Sun is really moving over Earth. We know that the Sun only appears to rise as the rotation of Earth carries us to a
place where we can see the Sun in our sky. Identify other common phrases that imply an Earth-centered viewpoint.

Patrick Vaughn

Numerade Educator

Problem 57

Flat Earth Society. Believe it or not, there is an organization called the Flat Earth Society. Its members hold that Earth is flat and that all indications to the contrary (such as pictures of Earth from space) are fabrications made as part of a conspiracy to hide the truth from the public. Discuss the evidence for a round Earth and how you can check it for yourself. In light of the evidence, is it possible that the Flat Earth Society is correct? Defend your opinion.

Julian Wong

Numerade Educator

Problem 58

Sky Information. Search the Web for sources of daily information about sky phenomena (such as lunar phases, times of sunrise and sunset, or dates of equinoxes and solstices). Identify and briefly describe your favorite source.

Donald Albin

Numerade Educator

Problem 59

Constellations. Search the Web for information about the constellations and their mythology. Write a short report about one or more constellations.

Narayan Hari

Numerade Educator

Problem 60

Upcoming Eclipse. Find information about an upcoming solar or lunar eclipse. Write a short report about how you could best observe the eclipse, including any necessary travel to a viewing site, and what you could expect to see. Bonus: Describe how you could photograph the eclipse.

Chris Johnson

Numerade Educator