Name
Teacher
Period
Date
25
Chapter
Earth, Sun, and Seasons
CHAPTER 25—SKILL SHEET 1: EARTH’S SEASONS
Copyright © 2007 AMSCO Publications, Inc.
Although the distance between Earth and the sun varies on an annual cycle, this change
is too small to cause our seasons. In fact, Earth is actually closest to the sun in the month
of January.
1
Our seasons are caused by the 23 2° tilt of Earth’s axis. This tilt causes the apparent
path of the sun through the sky to change throughout the year. Summer starts when the
noon sun is highest in the sky, as well as when the sun is in the sky for the greatest number of hours of the day. See Figure 25-1.
FIGURE 25-1. Earth’s seasons are caused by the tilt of Earth’s axis, which points to
Polaris throughout the year. Note that New York is turned toward the sun in our summer.
In the Northern Hemisphere, daylight is longest about June 21. That is when our sunlight is strongest and most direct. However, south of the equator, this is when the sun is
lowest in the sky and when daylight is shortest. Therefore, the seasons are six months out
of phase north and south of the equator.
Figure 25-2 shows that Earth is actually about 3 percent closer to the sun in our winter. This very small change in Earth-sun distance has very little effect on our weather. If
our changing distance from the sun caused the seasons, winter and summer would occur
at the same time north and south of the equator. However, they do not.
SKILL SHEET 1: EARTH’S SEASONS 281
Name
Teacher
Period
Date
152,000,000 km
147,000,000 km
FIGURE 25-2. Earth is actually slightly closer to the sun in our winter.
1. In what month is Earth farthest from the sun? July
2. Why does the changing distance between Earth and sun not affect the seasons?
The change in distance is relatively small.
3. What actually causes the seasons? The tilt of Earth’s axis
4. When it is spring in New York, what season is it in Argentina and South Africa?
Fall
The Sky
June Path
March & Sept.
Path
Sunrise
December
Path
S
5. According to Figure 25-3, approximately how high in the sky is the
noon sun in the New York region on
72°
June 21
North Pole
of the Sky
(to Polaris)
N
Of course, in our observations from
Earth we cannot see Earth from a distance.
What we observe is the changing of the
sun’s apparent path across the sky. This is
illustrated in Figure 25-3.
Sunset
7. What is the annual range (the change
47°
in altitude)?
282 CHAPTER 25 EARTH, SUN, AND SEASONS
W
Cc.
6. How high is the noon sun in New York
25°
on December 21?
FIGURE 25-3. The apparent path of the sun through
the sky changes in an annual cycle. This diagram
represents observations taken in central New York State.
LABORATORY MANUAL
Name
Teacher
Period
Date
8. How does this range of altitude compare with Earth’s tilt angle?
It is twice the tilt angle.
Each letter in Figure 25-4 represents a position of Earth in its annual
revolution around the sun. Base your
answers to items 9–18 on Figure 25-4.
9. What month is represented by
each letter in Figure 25-4?
A. June
B. September
C. December
D. March
For items 10–18 on the blank line
write the letter indicating the position
described by the statement.
FIGURE 25-4. The two enlarged Earths show that sunlight is
most concentrated where the sun is high overhead.
10. The day when the noon sun is
A
highest in New York:
A
11. The date of the most concentrated insolation in New York:
C
12. Our first day of winter:
13. First day of spring in New York
D
Copyright © 2007 AMSCO Publications, Inc.
14. Earth’s approximate closest approach to the sun (perihelion):
15. Autumnal equinox:
C
B
16. The beginning of summer in the Southern Hemisphere:
C
17. Earth’s greatest distance (approximate position) from the sun (aphelion):
18. The shortest day of the year in the United States:
A
C
SKILL SHEET 1: EARTH’S SEASONS 283
Name
Teacher
Period
Base your answers to items 19–24 on
Figure 25-5.
19. First day of our summer:
March 21
b
20. Of these four choices, Earth is closest
d
to the sun:
21. Matches position A on Figure 25-4:
b
NP a
Spring equinox
Dec. 21
b
NP
Summer
solstice
Winter
solstice
Sun
Fall equinox
23. When the South Pole is in bright
d
daylight:
NP
d
June 21
22. When the noon sun is lowest in the
d
sky in the United States:
24. Although Earth is closest to the sun
in January, why is it so cold for us in
that month?
Date
c
NP
Another View
of Earth's Orbit
(not to scale)
Sept. 23
FIGURE 25-5. Earth’s orbit as seen from far above.
From this point of view, the orbit of Earth looks perfectly
round.
Copyright © 2007 AMSCO Publications, Inc.
In January, Earth’s axis is tilted away from the sun.
284 CHAPTER 25 EARTH, SUN, AND SEASONS
LABORATORY MANUAL