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MAZER
Page 387
midnight
6 A.M.
noon
Lengths of Days
Seasonal temperatures depend on the amount of daylight, too. In
Sacramento, for example, the summer Sun heats the ground for about
15 hours a day, but in winter there may be only 9 hours of sunlight
each day. The farther you get from the equator, the more extreme
the changes in day length become. As you near one of the poles,
summer daylight may last for 20 hours or more.
6 P.M.
Near the pole in the summer, the Sun stays above
the horizon, so there is
no night. This series of
photographs was taken
over the course of a day.
Very close to the poles, the Sun does not set at all for six months at a
time. It can be seen shining near the horizon at midnight. Tourists often
travel far north just to experience the midnight Sun. At locations near
a pole, the Sun sets on an equinox and then does not rise again for six
months. Astronomers go to the South Pole in March to take advantage
of the long winter night, which allows them to study objects in the sky
without the interruption of daylight.
Very near the equator, the periods of daylight and darkness are
almost equal year-round—each about 12 hours long. Visitors who are
used to hot weather during long summer days might be surprised when
a hot, sunny day ends suddenly at 6 P.M. At locations away from the
equator, daylight lasts 12 hours only around the time of an equinox.
KEY CONCEPTS
CRITICAL THINKING
1. What causes day and night?
4. Apply If you wanted to enjoy
longer periods of daylight in
the summertime, would you
head closer to the equator or
farther from it? Why?
(8.4.e)
2. What happens to Earth’s axis
of rotation as Earth orbits
the Sun? (8.4.e)
3. How do the areas of sunlight
in the two hemispheres change
over the year? (8.4.e)
5. Compare and Contrast
How do the average temperatures and the seasonal changes
at the equator differ from those
at the poles?
CHALLENGE
6. Infer If Earth’s axis were tilted
so much that the North Pole
sometimes pointed straight at
the Sun, how would the hours
of daylight be affected at
your location?
Chapter 12: Earth, Moon, and Sun 387
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