Earth’s Days, Years, and Seasons Unit 4 Lesson 1 Part II Earth’s Days, Years, and Seasons Copyright © Houghton Mifflin Harcourt Publishing Company 1

Seasons change … What causes seasons? Unit 4 Lesson 1 Earth’s Days, Years, and Seasons Seasons change … What causes seasons? Most locations on Earth experience seasons. Each season is characterized by a pattern of temperature and other weather trends. We experience seasons due to changes in the intensity of sunlight and the number of daylight hours as Earth revolves around the sun. Copyright © Houghton Mifflin Harcourt Publishing Company 2

Unit 4 Lesson 1 Earth’s Days, Years, and Seasons What causes seasons? At an equinox, sunlight shines equally on the Northern and Southern hemispheres. Half of each hemisphere is lit, and half is in darkness. As Earth moves along its orbit, the sunlight reaches more of one hemisphere than the other. At a solstice, the area of sunlight is at a maximum in one hemisphere and at a minimum in the other hemisphere. Copyright © Houghton Mifflin Harcourt Publishing Company 3

Unit 4 Lesson 1 Earth’s Days, Years, and Seasons What causes seasons? During the September equinox, sunlight shines equally on both poles. During the March equinox, half of each hemisphere is lit, and the sunlight is centered on the equator. Copyright © Houghton Mifflin Harcourt Publishing Company 4

Unit 4 Lesson 1 Earth’s Days, Years, and Seasons What causes seasons? At the December solstice, the North Pole leans away from the sun and is in complete darkness, and the South Pole is in complete sunlight. At the June solstice, the North Pole leans toward the sun and is in complete sunlight, and the South Pole is in complete darkness. Copyright © Houghton Mifflin Harcourt Publishing Company 5

What causes seasons? Unit 4 Lesson 1 Earth’s Days, Years, and Seasons Copyright © Houghton Mifflin Harcourt Publishing Company 6