8
ChapterbyChapter Guide
we find that 1 lightyear
9.46
10
12
km, so
we can convert:
We can now find the ratio of the two
diameters:
The diameter of the Milky Way Galaxy is about
3.5 trillion times as large as the diameter of
Saturn’s rings!
44.
a.
The circumference of Earth is 2
6,380 km
40,087 km. At a speed of
100 km/hr, it would take:
to drive around Earth. That is, a trip around
the equator at 100 km/hr would take a little
under 17 days.
b.
We find the time by dividing the distance
to the planet from the Sun by the speed of
100 km/hr. It would take about 170 years
to reach Earth and about 6,700 years to
reach Pluto (at their mean distances).
c.
Similarly, it would take 6,700 years to
drive to Pluto at 100 km/hr. FYI: The fol
lowing table shows the driving times from
the Sun to each of the planets at a speed of
100 km/hr.
d.
We are given the distance to Alpha
Centauri in lightyears; converting to
kilometers, we get:
At a speed of 100 km/hr, the travel time to
Proxima Centauri would be about:
It would take some 47 million years to
reach Proxima Centauri at a speed of
100 km/hr.
45.
a.
To reach Alpha Centauri in 100 years, you
would have to travel at 4.4/100
0.044 of
the speed of light, which is about 13,200
km/s or nearly 50 million km/hr.
b.
This is about 1,000 times the speed of our
fastest current spacecraft.
=
4.7
*
10
7
yr
4.16
*
10
13
km
,
100
km
hr
=
4.16
*
10
13
km
*
1 hr
100 km
*
1 day
24 hr
*
1 yr
365 day
4.4 light years
*
9.46
*
10
12
km
1 light year
=
41.6
*
10
12
km
40,087 km
,
100 km/hr
=
40,087 km
*
1 hr
100 km
*
1 day
24 hr
=
16.7 days
=
9.46
*
10
17
km
2.7
*
10
5
km
=
3.5
*
10
12
ratio
=
diameter of Milky Way
diameter of Saturn’s rings
100,000 light years
*
9.46
*
10
12
km
1 light year
=
9.46
*
10
17
km
Planet
Driving Time
Mercury
66 years
Venus
123 years
Earth
170 years
Mars
259 years
Jupiter
888 years
Saturn
1,630 years
Uranus
3,300 years
Neptune
5,100 years
Pluto
6,700 years
Chapter 2. Discovering the Universe for Yourself
This chapter introduces major phenomena of the sky, with emphasis on:
•
The concept of the celestial sphere.
•
The basic daily motion of the sky, and how it varies with latitude.
•
The cause of seasons.
•
Phases of the Moon and eclipses.
•
The apparent retrograde motion of the planets, and how it posed a problem for
ancient observers.
As always, when you prepare to teach this chapter, be sure you are familiar with the
relevant media resources (see the complete, sectionbysection resource grid in Appendix 3
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Part I
9
of this Instructor’s Guide) and the online quizzes and other study resources available on
the MasteringAstronomy Web site.
What’s New in the Fourth Edition That Will Affect
My Lecture Notes?
As everywhere in the book, we have revised to improve the text flow, added optional
Cosmic Calculations boxes, improved art pieces, and added new illustrations. The art
changes, in particular, will affect what you wish to show in lecture. We have not made
any substantial content or organizational changes to this chapter.
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 Fall '09
 unknown
 apparent retrograde motion

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