Figure 10 The seasons are caused by the tilt of Earth's axis as it revolves around the sun. Interpreting Visuals When is the south end of Earth's axis tilted most toward the sun?
ddThe seasons are not affected by Earth's changing distance from the sun. In fact, in the Northern Hemisphere, Earth is closer to the sun during winter than it is during summer.
Equinoxes
Look at Figure 10. Notice that halfway between the solstices are two days, called equinoxes. The equinoxes mark the beginning of spring and autumn. At an equinox, neither hemisphere is tilted toward the sun, and the lengths of daylight and of darkness are approximately equal. The vernal equinox, which occurs about March 21 in the Northern Hemisphere, marks the start of spring. The autumnal equinox, which occurs about September 22 in the Northern Hemisphere, marks the start of autumn. On these two days, the noon sun is directly overhead at the equator. Sunlight reaches the Northern Hemisphere and Southern Hemisphere in equal amounts on the equinoxes.
Section 24.2 Assessment
Reviewing Concepts
Describe two ways in which Earth moves in space.- What are three zones on Earth's surface that are based on latitude? What are their characteristics?
- What determines the change in seasons?
- Describe one effect of Earth's rotation.
Critical Thinking
Classifying Classify each of the following latitudes as part of the tropic, temperate, or polar zones: 15° north, 29° south, and 70° north.
Inferring What is Earth's orientation at the time of the winter solstice in the Southern Hemisphere? Explain.
Comparing and Contrasting How are solstices and equinoxes similar? How are they different?
Writing in Science
Cause and Effect Write a paragraph describing how life in your community might be different if Earth's axis were not tilted. (Hint: Consider how the tilt of Earth's axis affects the seasons.)
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