The Reasons for Seasons 1212022 The Seasons 1

The Reasons for Seasons 1/21/2022 The Seasons 1

Day Night Cycle 1/21/2022 The Seasons 2

Rotation vs. Revolution • Rotation is the spin of the Earth around its axis. – The Earth rotates once a day (every 24 hours). • Revolution is the orbit of one object around another. – The Earth revolves around the Sun every 365 days. 1/21/2022 The Seasons 3

Tilt of the Earth’s Axis • The axis around which the Earth rotates is tilted by 23. 5 degrees • This is what causes seasons. 1/21/2022 The Seasons 4

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Tilt of the Earth’s Axis 1/21/2022 The Seasons 6

Equinoxes and Solstices • The Vernal (Spring) Equinox (March) Equal day and night • The Summer Solstice (June) Longest day of the year • The Autumnal (Fall) Equinox (Sept. ) Equal day and night • The Winter Solstice (December) Shortest day of the year 1/21/2022 The Seasons 7

Midnight Sun 1/21/2022 The Seasons 8

Earth on June 21 1/21/2022 The Seasons 9

Seasons Misconception • Many people think that the seasons are due to the distance of the Earth from the Sun. However: – The Earth’s orbit around the Sun is nearly a perfect circle. The Earth is slightly closer to the Sun in January and farther from the Sun in July. – If the seasons were due to our distance from the Sun both hemispheres would have the same seasons at the same time. 1/21/2022 The Seasons 10

Orbit of the Earth 1/21/2022 The Seasons 11

The Seasons • In fact, the seasons are due to the tilt of the Earth’s axis. Consider what happens on June 21 when the northern hemisphere of the Earth is tilted toward the Sun: • The sunlight strikes the ground more vertically than in December. The light is spread out over less ground and heats the ground better. • The Sun is above the horizon for a longer period of time. 1/21/2022 The Seasons 12

Earth on June 22 1/21/2022 The Seasons 13

Earth on December 22 1/21/2022 The Seasons 14

A. M. and P. M. • At midday, the Sun is on your meridian. – This occurs close to, or at, noon. – A. M. comes from ante meridiem (before midday) – P. M. comes from post meridiem (after midday) 1/21/2022 The Seasons 15

Daylight Saving Time • During the late spring, summer, and early fall, we set out clocks ahead to have an extra hour of daylight at the end of the day. – This change in time is called Daylight Saving Time. – The idea of changing our clocks was first used in the United States during World War I to conserve energy. • Since 1986, the United States has set our clocks one hour ahead on the first Sunday in April and one hour behind on the last Sunday in October. – Spring ahead, fall back. 1/21/2022 The Seasons 16

animations • Seasons use code cfp-5012 • http: //esminfo. prenhall. com/science/geoani mations/animations/01_Earth. Sun_E 2. html Cosmic Map • http: //www. nationalgeographic. com/xpediti ons/activities/07/popup/cosmic. html

Now, see what you know about the seasons! • http: //www. teachersdomain. org/ext/ess 05_ int_seasonsgame/index. html