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Science and Society

Saving Time?
he purpose of daylight saving time is Americans who like daylight saving clock, so they have to plan all their nonfarm
Tto make better use of daylight during time say they like it because it gives them interactions on a different schedule.
the summer by moving an hour of daylight more light in the evenings, and it saves en-
from the morning to the evening. In the ergy. Some people do not like daylight sav- QUESTIONS TO DISCUSS
United States, daylight saving time is ob- ing time because it requires them to reset all
served from the second Sunday in March their clocks and adjust their sleep schedule Divide your group into two subgroups, one
to the first Sunday in November. Clocks are twice a year. They also complain that the act representing those who like daylight saving
changed on these Sundays according to the of changing the clock is not saving daylight time and the other representing those who
saying, “Spring ahead, fall back.” Arizona at all, but it is sending them to bed an hour do not. After a few minutes of preparation,
and Hawaii choose not to participate and earlier. Farmers also complain that plants have a short debate about the advantages
stay on standard time all year. and animals are regulated by the Sun, not the and disadvantages of daylight saving time.

FIGURE 16.24 The standard time zones.

cumulative time zone changes (Figure 16.25). A traveler Yearly Time
crossing the date line gains or loses a day just as crossing a A year is generally defined as the interval of time required for
time zone boundary results in the gain or loss of an hour. A Earth to make one complete revolution in its orbit. As was the
person moving across the line while traveling westward gains case for definitions of a day, there are different definitions of
a day; for example, the day after June 2 would be June 4. A what is meant by a year. The most common definition of a year
person crossing the line while traveling eastward repeats a is the interval between two consecutive spring equinoxes, which
day; for example, the day after June 6 would be June 6. Note is known as the tropical year (trope is Greek for “turning”). The
that the date line is curved around land masses to avoid local tropical year is 365 days, 5 hours, 48 minutes, 46 seconds, or
confusion. 365.24220 mean solar days.

16-13 CHAPTER 16 Earth in Space 417