Question 1.1

Where is the horizon?

• a. directly overhead
• b. along the celestial equator
• c. on the boundary between land and sky
• d. along the path that the Sun follows throughout the day
• e. the line running from due north, directly overhead, ending due south

Question 1.2

How many constellations are there?

• a. 2
• b. 12
• c. 13
• d. 56
• e. 88

Question 1.3

Which of the following lies on the celestial sphere directly over Earth’s equator?

• a. ecliptic
• b. celestial equator
• c. north celestial pole
• d. south celestial pole
• e. horizon

Question 1.4

The length of time it takes Earth to orbit the Sun is

• a. an hour
• b. a day
• c. a month
• d. a year
• e. a century

Question 1.5

In Figure 1-8, what is another name for the “Sun’s annual path around the celestial sphere”?

Question 1.6

How are constellations useful to astronomers?

Question 1.7

What is the celestial sphere, and why is this ancient concept still useful today?

Question 1.8

What is the celestial equator, and how is it related to Earth’s equator? How are the north and south celestial poles related to Earth’s axis of rotation?

Question 1.9

What is the ecliptic, and why is it tilted with respect to the celestial equator?

Question 1.10

By about how many degrees does the Sun move along the ecliptic each day? Explain why.

Question 1.11

Through how many constellations does the Sun move every day? Explain why.

Question 1.12

Through how many constellations does the Sun move every year? Which ones are they?

Question 1.13

Why does the tilt of Earth’s axis relative to its orbit cause the seasons as Earth revolves around the Sun? Draw a diagram to illustrate your answer.

Question 1.14

What are the vernal and autumnal equinoxes? What are the summer and winter solstices? How are these four events related to the ecliptic and the celestial equator?

Question 1.15

What is precession, and how does it affect our view of the heavens?

Question 1.16

How does the daily path of the Sun across the sky change with the seasons?

Question 1.17

Why is it warmer in the summer than in the winter?

Question 1.18

Why is it convenient to divide Earth into time zones?

Question 1.19

Why does the Moon exhibit phases?

Question 1.20

What is the difference between a sidereal month and a synodic month? Which is longer? Why?

Question 1.21

What is the line of nodes, and how is it related to solar and lunar eclipses?

Question 1.22

What is the difference between the umbra and the penumbra of a shadow?

Question 1.23

What is a penumbral eclipse of the Moon? Why is it easy to overlook such an eclipse?

Question 1.24

Which type of eclipse—lunar or solar—have most people seen? Why?

Question 1.25

How is an annular eclipse of the Sun different from a total eclipse of the Sun? What causes this difference?

Question 1.26

When is the next leap year?

Question 1.27

At which phase(s) of the Moon does a solar eclipse occur? A lunar eclipse?

Question 1.28

Is it safe to watch a solar eclipse without eye protection? A lunar eclipse?

Question 1.29

During what phase is the Moon “up” least in the daytime?

Question 1.30

During which phase(s) does the Moon rise after sunrise and before sunset? After sunset and before sunrise? At sunset? At sunrise?

Question 1.31

Why can’t a person in Australia use the Big Dipper to find north?

Question 1.32

Are there any stars in the sky that are not members of a constellation? If so, which ones?

Question 1.33

At what places on Earth is Polaris seen on the horizon?

Question 1.34

Where do you have to be on Earth to see the Sun at your zenith? If you stay at one such location for a full year, on how many days will the Sun pass through the zenith?

Question 1.35

Where do you have to be on Earth to see the south celestial pole at your zenith? What is the maximum possible elevation (angle) of the Sun above the horizon at that location? On what date is this maximum elevation achieved?

Question 1.36

Where on the horizon does the Sun rise at the time of the vernal equinox?

Question 1.37

Consult a star map that shows the precession path of the south celestial pole and determine which, if any, of the bright southern stars could someday become south celestial pole stars.

Question 1.38

Are there stars in the sky that never set where you live? Are there stars that never rise where you live? Does your answer depend on your location on Earth? Why or why not?

Question 1.39

Using a diagram, demonstrate that your latitude on Earth is equal to the altitude of the north (or south) celestial pole above your northern (or southern) horizon.

Question 1.40

Using a star map, determine which bright stars, if any, could someday mark the location of the vernal equinox. Give the approximate years when this should happen.

Question 1.41

What is the phase of the Moon if it

• a. rises at 3 a.m.?
• b. sets at 9 p.m.?
  
  At what time does
• c. the full Moon set?
• d. the first quarter Moon rise?

Question 1.42

What is the phase of the Moon if, on the first day of spring, the Moon is located at the position of

• a. the vernal equinox?
• b. the summer solstice?
• c. the autumnal equinox?
• d. the winter solstice?

Question 1.43

* How many more sidereal months than synodic months are there in a year? Why?

Question 1.44

How do we know that the phases of the Moon are not due to the Moon moving through Earth’s shadow?

Question 1.45

Do the paths of total solar eclipses fall more frequently on oceans or on land? Explain.

Question 1.46

Can one ever observe an annular eclipse of the Moon? Why or why not?

Question 1.47

During a lunar eclipse, does the Moon enter Earth’s shadow from the east or the west? Explain your answer.

Question 1.48

How long was the exposure for the photograph of circumpolar star trails in Figure 1-11?

Question 1.49

Determine which stars whose paths are shown in Figure 1-11 are not circumpolar. An easy way to write the answer is in terms of distance on the photograph from the location of the south celestial pole.

Question 1.50

How does Figure 1-11 show that there is no bright “South Pole” star?

Question 1.51

Do we see all of the Moon’s surface from Earth? Why or why not? Hint: Carefully examine the photographs in Figure 1-22.

Question 1.52

Explain why the waning gibbous Moon, third quarter Moon, and waning crescent Moon photographs in Figure 1-22 are correctly oriented as seen from Earth.

Question 1.53

* Assuming that the Sun makes an angle of ½° in our sky and is at a distance of 1.496 × 10¹¹ m, what is the Sun’s diameter? Divide this value by 2 to find the Sun’s radius and explain why this result is slightly different from the value given in Appendix E-8 at the back of the book.

Question 1.54

Make a drawing of an annular solar eclipse as seen from space similar to Figure 1-27. Be sure to make clear how it differs from a total solar eclipse.

Question 1.55

Which of the five images of the Sun in Figure 1-29 is the first and which is the last in the sequence shown? Justify your answer.

Question 1.56

Why is a small crescent of light often observed on the Moon when it is exactly in the new phase?

Question 1.57

Examine the list of the 88 constellations in Appendix E-7. Are there any constellations whose names obviously date from modern times? Where are these constellations located? Why do they not have ancient names?

Question 1.58

In his novel King Solomon’s Mines, H. Rider Haggard described a total solar eclipse that was seen in both South Africa and the British Isles. Is such an eclipse possible? Why or why not?

Question 1.59

Describe how a lunar eclipse would look if Earth had no atmosphere.

Question 1.60

Examine a listing of total solar eclipses over the next several decades. What are the chances that you might be able to travel to one of the eclipse paths? Do you think you might go through your entire life without ever seeing a total eclipse of the Sun?

Question 1.61

The Moon moved about Earth in an orbit perpendicular to the plane of Earth’s orbit? What would the cycle of lunar phases be? Would solar and lunar eclipses be possible under these circumstances?

Question 1.62

Earth’s axis of rotation were tilted at a different angle? What would the seasons be like where you are now if the axis of rotation were

• a. 0° and
• b. 45° to its orbital plane?

What would be different about the seasons and the day-night cycle if you lived at one of Earth’s poles in these two situations?

Question 1.63

You watched Earth from the Moon? What would you see for Earth’s

• a. daily motion?
• b. motion along the celestial sphere?
• c. cycle of phases?

Question 1.64

The Moon didn’t rotate? Describe how its surface features would appear from Earth—that is, would we see all sides of it over time? Why or why not? (Ignore the change in phases when discussing its appearance.) Carefully study the photographs in Figure 1-22 and state whether the same features are visible at all times or whether we see different features over time. (Again, ignore the phases.) What can you conclude about whether the Moon actually rotates?

Question 1.65

Search the Web and identify at least four cultures whose stories were used to name modern constellations. Briefly relate the stories of a constellation from each culture.

Question 1.66

Search the Web for information about the Great Nebula of Orion (see label on Figure 1-4b; it is also called the Orion Nebula). Can the Great Nebula be seen with the naked eye? Does it exist alone in space or is it part of a larger system of interstellar material? What has been learned by examining the Great Nebula with telescopes sensitive to infrared light?

Question 1.67

Search the Web for information about the national flags of Australia, New Zealand, and Brazil and the state flag of Alaska. Which stars are depicted on these flags? Explain any similarities or differences among these flags.

Question 1.68

Search the Web for the English meaning of the Japanese word subaru. Make a drawing of the Subaru car’s emblem and explain it.

Question 1.69

Use the U.S. Naval Observatory’s Web site to determine the times of sunset and sunrise on

• a. your birthday and
• b. today’s date.

Are the times the same? Explain why or why not.

Question 1.70

Use data in this book or search the Web for information about the next total solar eclipse. Through which major cities, if any, does the path of totality pass? What is the maximum duration of totality? Find a location where this maximum duration is observed. Will the eclipse be visible (even as a partial eclipse) from your present location?

Question 1.71

Search the Web for information about the next total lunar eclipse. Will the total phase of the eclipse be visible from your present location? If not, will the penumbral phase be visible? Draw a picture of the Sun, Earth, and the Moon at totality and indicate your location on the drawing of Earth.

Question 1.72

Access the animation “The Moon’s Phases” in Chapter 1 of the Discovering the Universe Web site. This shows the Earth-Moon system as seen from a vantage point above Earth’s North Pole.

• a. Describe where you would be on the diagram if you were on the equator and the time were 6:00 p.m.
• b. If it were 6:00 p.m. and you were standing on Earth’s equator, would a third quarter Moon be visible? Why or why not? If the Moon would be visible, describe its appearance.

Question 1.73

Describe the Orion constellation.

Question 1.74

In what season in the southern hemisphere is Earth closest to the Sun? In what season in the northern hemisphere is Earth closest to the Sun? If the changing distance from Earth to the Sun caused the seasons, what should be true about the answers to the first two parts of this question?

Question 1.75

What observational evidence do we have that the Moon does not make its own light?

Question 1.76

What is the difference between the “far” side of the Moon and the “dark” side of the Moon?

Question 1.77

Through how many constellations does the Sun pass each year? What are these constellations called?

Question 1.78

Which of the following statements is correct for someone standing at one of Earth’s poles?

• a. The Sun rises and sets every day.
• b. The Sun is directly overhead on the summer solstice in that hemisphere.
• c. The Sun is in the sky continuously for 6 months.
• d. The Moon is never visible.
• e. The stars rise vertically and set vertically.

Question 1.79

On a clear, cloud-free night, use the star charts at the end of this book to see how many constellations of the zodiac you can identify. Which ones are easy to find? Which are difficult?

Question 1.80

If you have access to the Starry Night™ planetarium software, install it on your computer. There are several guides to the use of this software. As an initial introduction, you can run through the step-by-step basics of the program by clicking the Sky Guide tab to the left of the main screen and then clicking the Starry Night basics hyperlink at the bottom of the Sky Guide pane. A more comprehensive guide is available by choosing the Student Exercises hyperlink and then the Tutorial hyperlink. A User’s Guide to this software is available under the Help menu. As a start, you can use this program to determine when the Moon is visible today from your location. If the viewing location in the Starry Night control panel is not set to your location, select Set Home Location…in the File menu (on a Mac, this command is found under the Starry Night menu). Click the List tab in the Home Location dialog box; then select the name of your city or town and click the Save As Home Location button. Next, use the hand tool to explore the sky and search for the Moon by moving your viewpoint around the sky. (Click and drag the mouse to achieve this motion.) If the Moon is not easily seen in your sky at this time, click the Find tab at the top left of the main view. The Find pane that opens should contain a list of Solar System objects. Ensure that there is no text in the edit box at the top of the Find pane. If the message “Search all Databases” is not displayed below this edit box, then click the magnifying glass icon in the edit box and select Search All from the drop-down menu that appears. Click the + symbol to the left of the Earth listing to display The Moon and double-click on this entry in the list in order to center the view upon the Moon. (If a message is displayed indicating that “the Moon is not currently visible from your location,” click on the Best Time button to advance to a more suitable time). You will see that the Moon can be seen in the daytime as well as at night. Note that the Time Flow Rate is set to 1x, indicating that time is running forward at the normal rate. Note also the phase of the Moon. (a) Estimate how long it will take before the Moon reaches its full phase. Set the Time Flow Rate to 1 minutes. (b) Find the time of moonset at your location. (c) Determine which, if any, of the following planets are visible tonight: Mercury, Venus, Mars, Jupiter, and Saturn. (Hint: Use the Find pane and click on each planet in turn to explore the positions of these objects.) Feel free to experiment with the many features of Starry Night™.

Question 1.81

Use the Starry Night™ program to measure angular spacing between stars in the sky. Open Favourites > Explorations > N Pole to display the northern sky from Calgary, Canada, at a latitude of 51°. This view shows several asterisms, or groups of stars, outlined and labeled with their common names. The stars in the Big Dipper asterism outline the shape of a “dipper” used for scooping water from a barrel. The two stars in the Big Dipper on the opposite side of the scoop from the handle, Merak and Dubhe, can be seen to point to the brightest star in the Little Dipper, the Pole Star. The Pole Star is close to the North Celestial Pole, the point in the sky directly above the North Pole of Earth. It is thus a handy aid to navigation for northern hemisphere observers because it indicates the approximate direction of true north. Measure the spacing between the two “pointer stars” in the Big Dipper and then the spacing between the Pole Star and the closest of the pointer stars, Dubhe. (Hint: These measurements are best made by activating the angular separation tool from the cursor selection tool on the left side of the toolbar.) (a) What is the angular distance between the pointer stars Merak and Dubhe? (b) What is the angular spacing, or separation, between Dubhe (the pointer star at the end of the Big Dipper) and the Pole Star? (c) Approximately how many pointer-star spacings are there between Dubhe and the Pole Star? Explore the apparent motion of the sky as Earth rotates. Note that the Time Flow Rate is set to 1 minute. Click the Play button in the toolbar to start time flow. Note that the Pole Star will appear to remain fixed in the sky as time progresses because it lies very close to the North Celestial Pole. Select Edit > Undo Time Flow or File > Revert from the menu to return to the initial view. Select View > Celestial Guides > Celestial Poles from the menu to indicate the position of the North Celestial Pole on the screen. Right-click on the Pole Star (Control-click on a Mac) and select Centre from the drop down menu to center the view on the Pole Star. Zoom in and use the angular separation tool to measure the angular spacing between the Pole Star and the North Celestial Pole. (d) What is the angular separation between the Pole Star and the North Celestial Pole? (e) Select File > Revert from the menu and use the angular separation tool to measure the angle between the Pole Star and the horizon at Calgary. (f) What is the relationship between this angle and the latitude of Calgary (51°)? Open Favourites > Explorations > S Pole to view the southern sky from Brisbane, Australia, at a southern latitude of 27½°. For observers in the southern hemisphere, there is no prominent star at or near to the position of the South Celestial Pole so its position is displayed on the view. The key asterism for estimating the position of the South Celestial Pole is the Southern Cross. (g) Use the angular separation tool to measure the angle between the fainter of the two stars making up the major axis of the cross, Gacrux, and the brighter star, Acrux. Extend this line towards the pole to demonstrate that this alignment is not exact. (h) Measure the angle between Acrux and the South Celestial Pole. (i) How many “pointer-star” spacings does this angle represent? (j) Measure the angle between the pole and the horizon at Brisbane. (k) What is the relationship between this angle and the latitude of the observer? Click the Play button to demonstrate that the sky appears to rotate about this South Celestial Pole because of the rotation of Earth.

39

Question 1.82

Use Starry Night ™ to help you to identify the constellations of the zodiac that are visible in your sky this evening. Click the Home button, followed by the Sunset button, and then use the S key on your keyboard to view the southern horizon if you are in the northern hemisphere. (Use the N key to view the northern horizon if you are in the southern hemisphere.) Select View > Constellations > Zodiac from the menu to outline these constellations with stick figures. Use the hand tool to “grab” and move the sky to see this band of constellations. Right-click (PC) or Ctrl-click (Mac) on these figures to display a menu that identifies the constellation in the topmost Select command. Alternatively, select Labels > Constellations to label every zodiac constellation. Advance time by a few hours and use the hand tool to see more of the zodiacal constellations. The constellations of the zodiac contain the path of the Sun across the sky in the course of a year. To demonstrate this, you can display the Sun’s path, known as the ecliptic, on the sky by selecting View > Ecliptic Guides > The Ecliptic from the menu. You can also display classical images of constellations that indicate where these star patterns acquired their names in antiquity by clicking on View > Constellations > Auto Identify, after which the constellation name and classical image will appear whenever you center a constellation on the screen. (a) Adjust time and date to determine the neighboring zodiacal constellations to the constellation Leo. (b) Click the Home button in the toolbar to return to your home location and to the present time and click the Stop button to stop the advance of time. You can determine which zodiac constellation the Sun is passing through today by changing the time in the toolbar to 12:00:00 PM and using the hand tool to find the Sun in the sky. You can remove the blue daylight sky by selecting View > Hide Daylight from the menu. Display the modern boundaries of constellations by clicking View > Constellations > Boundaries. This will allow you to be more specific about the location of the Sun within a specific constellation. Right-click (PC) or Ctrl-click (Mac) on the Sun and select Centre from the menu. Where is the Sun from your location at the present time and date? (c) You can now advance or reverse time in intervals of 1 day by using the D and Shift-D keys on your keyboard and track the Sun completely around the zodiac. Make a list of the names of these constellations, adding the dates of boundary crossing between the names of each constellation. (d) Will this Sun’s location be different when viewed from the opposite hemisphere from the one in which you are located?

Question 1.83

Use Starry Night™ to observe the diurnal motion of the sky. First, set Starry Night™ to display the sky as seen from where you live, if you have not already done so. To do this, select File > Set Home Location…(Starry Night > Set Home Location on a Mac) and click on the List tab to find the name of your city or town. Highlight the name and note the latitude of your location as given in the list and click the Save As Home Location button. Select Options > Other Options > Local Horizon… from the menu. In the Local Horizon Options dialog box, click on the radio button labeled Flat in the Horizon style section and click OK. For viewers in the northern hemisphere, press the N key (or click the N button in the Gaze section of the toolbar) to set the gaze direction to the northern sky. If your location is in the southern hemisphere, press the S key (or click the S button in the Gaze section of the toolbar) to set the gaze direction to the south. Select Hide Daylight under the View menu to view the present sky without daylight. Select View > Constellations > Astronomical and View > Constellations > Labels to display the constellation patterns on the sky. In the toolbar, click on the Time Flow Rate control and set the time step to 1 minute. Then click the Play button to run time forward. (The rapid motions of artificial Earth-orbiting satellites can prove irritating in this view. You can remove these satellites by clicking on View > Solar System and turning off Satellites). (a) Do the stars appear to rotate clockwise or counter-clockwise? Explain this observation in terms of Earth’s rotation. (b) Are any of the stars circumpolar, that is, do they stay above your horizon for the full 24 hours of a day? If some stars at your location are circumpolar, adjust time and locate a star that moves very close to the horizon during its diurnal motion. Click the Stop button and right-click (Ctrl-click on a Mac) on the star and then select Show Info from the contextual menu to open the Info pane. Expand the Position in Sky layer and note the star’s declination (its N-S position on the sky with reference to a coordinate system whose zero value is the projection of Earth’s equator). (c) How is this limiting declination, above which stars are circumpolar, related to your latitude, noted above?

• (i) The limiting declination is equal to the latitude of the observer’s location.
• (ii) The limiting declination is equal to (90 – latitude)
• (iii) There is no relationship between this limiting declination and the observer’s latitude.

(d) Now center your field of view on the southern horizon (if you live in the northern hemisphere) or the northern horizon (if you live in the southern hemisphere) and click Play to resume time flow. Describe what you see. Are any of these stars circumpolar?