Scientists use lines of latitude to mark out three different types of regions within which temperatures are generally similar: the tropic, temperate, and polar zones. Between the latitudes of 23.5° south and 23.5° north is the tropic zone, where Earth is generally warm. From 23.5° north to 66.5° north and from 23.5° south to 66.5° south are the temperate zones, which are generally cooler than the tropics. From 66.5° north to the North Pole and from 66.5° south to the South Pole are the polar zones, which are generally cold.
Which is the coldest type of latitude zone?
The Seasons
Most of the United States is in the temperate zone. In much of the country, therefore, temperature and other weather conditions change over the year with the cycle of the seasons. What causes these seasonal changes? The answer is related to Earth's rotation and its revolution.
Earth's axis of rotation is not straight up and down. Instead, the axis tilts at an angle of about 23.5° relative to a line perpendicular to its orbital path. As Earth orbits the sun, the north end of Earth's axis points in the same direction—toward the North Star. But the orientation of Earth's axis changes relative to the sun over the course of a year. The seasons are caused by the tilt of Earth's axis as it moves around the sun.
Solstices
Because Earth's axis is tilted, the latitude at which the noon sun appears directly overhead changes each day according to a yearly cycle. A solstice (SOHL stis) occurs on the two days each year when the sun is directly overhead at latitude 23.5° north or 23.5° south. In the Northern Hemisphere, the summer solstice, which marks the beginning of summer, occurs around June 21. At this time, the Northern Hemisphere is tilted toward the sun, so it receives more sunlight than the Southern Hemisphere. On this day, daylight hours are longest in the Northern Hemisphere and shortest in the Southern Hemisphere.
Six months later, on about December 21, the winter solstice, which marks the beginning of winter, occurs in the Northern Hemisphere. On the winter solstice, the Northern Hemisphere is tilted away from the sun. As a result, the Northern Hemisphere now receives less sunlight than the Southern Hemisphere. At this time, the daylight hours are shortest in the Northern Hemisphere, but longest in the Southern Hemisphere.
Figure 8 The angle that sunlight strikes Earth's surface varies with latitude. As a result, it is generally warmer near the equator than near the poles.
Interpreting Diagrams Which latitude zone receives the most direct sunlight?
Figure 9 In the temperate zones, the beginning of autumn brings cooler weather and colorful leaves.
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