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L2 Earth's Tilted Axis Why Are There Different Seasons?

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L2 Earth's Tilted Axis Why Are There Different Seasons? L2 Earth's Tilted Axis Why are there different seasons? Watch this time-lapse video and answer the following: Trees, bushes, grass, leaves. Time is sped up. •What do you observe in this video clip? •What is changing? The trees grow leaves, change colors, and then lose their leaves. The ice and snow on the ground thaw out. What patterns have you observed in the seasonal changes? Brainstorm as many as you can: • • • • • • • Phenomenon: Each year, trees sprout leaves which grow, change color, die, and fall off. Some locations experience all four seasons. Other locations may experience only some of the seasons (i.e., some locations have very mild winters with cool, but not cold winters. These locations rarely see snow in the winter). What seasons does your location experience? How can you explain why this is different than other locations around the country? •Sometimes the Northern Hemisphere is pointing toward the sun. •Sometimes the Northern Hemisphere is pointing away from the sun. •Sometimes Earth’s axis is neither pointing toward or away from the sun. Introduction (p23) The weather is warm in spring and trees begin to grow new leaves. Then, summer comes, hot and bright. The weather cools off in autumn, and some trees begin to lose their leaves. Before long, it is winter, the coldest time of the year. The pattern of the seasons continues as the weather warms up and spring occurs again. A change in temperature is just one pattern that occurs with the change in seasons. What other patterns can you observe over the course of a year? You may notice that the sun is in the sky for more time each day during the summer. In the winter, the days are shorter because the sun is not in the sky for as long. You may also notice that the sun travels higher above the horizon during the summer than during the winter. Are there any other patterns that you have observed? How does the orientation of the Earth relative to the sun cause these seasonal patterns? So far, you have learned about patterns of celestial objects and how they are caused by Earth's motion. In this lesson, you will continue to explore some cause and effect relationships related to patterns you can observe on Earth's surface. You will first get an overview of the many seasonal patterns observed on Earth. Then, you will learn how the angle of sunlight hitting Earth causes uneven heating of Earth's surface. Next, you will explore how Earth's axis is tilted and how this tilt causes seasonal patterns. Finally, you will read about how the sun's path in the sky changes over the course of a year and that ancient people tracked changes in the sun's path to monitor the seasons. 1. The Seasons (p24) A pattern is something that happens in a regular and repeated way. Every year, you experience a pattern of temperature changes as Earth revolves around the sun. How you experience seasons depends on where you are on Earth. • Much of the United States, such as New York and Alaska, has cold winters and hot summers. • other places at or near Earth's poles tend to become very cold in the winter and remain somewhat cool in the summer. • Hawaii, on the other hand, does not have as much variation in temperature because it is closer to the equator. The times of the year that you experience the seasons also depends on your location on Earth. • Northern Hemisphere, December, January, and February are winter months, and June, July, and August are summer months. • Southern Hemisphere, the seasons are opposite! December is the start of summer, and June is the start of winter. 1. The Seasons (p24) The seasons is how long the sun is visible in the sky. (The timing of sunrise and sunset) • In the winter, days are shorter because the sun is not in the sky for as long. • The sun rises later in the morning and sets earlier in the evening. • In the summer, days are longer because the sun is in the sky for a longer time • the sun rises earlier and sets later. Where the sun rises and sets changes with the seasons. In the Northern Hemisphere, the sun rises and sets farther south in the winter than it does in the summer. In the Southern Hemisphere, the sun rises and sets farther north in the winter than it does in the summer. All the differences in the seasons, including changes in temperature, sunrise, and sunset, are caused by changes in the position of Earth's axis relative to the sun. Annotate the calendar to show approximately when the four seasons occur during the year. Seasons of 2019 Astronomical Meteorological Start Start Wednesday, SPRING March 20, 5:58 Friday, March 1 P.M. EDT Friday, June 21, SUMMER Saturday, June 1 11:54 A.M. EDT Monday, Sunday, FALL September 23, September 1 3:50 A.M. EDT Saturday, Sunday, December WINTER December 21, 1 11:19 P.M. EST Investigation 1: Modeling the Seasons Earth keeps its tilt (Axis pointed towards Polaris) throughout its orbit. Now you will model the orbit using an inflatable Earth. Your bodies will represent Earth’s orbit. •How should you arrange yourselves to model the orbital path of Earth around the sun? Form a circle with the sun in the center. You should all be about the same distance away from the sun. •We will pass around an inflatable Earth to represent Earth’s revolution over a year. •How should you orient the inflatable Earth? The North Pole should always be pointing toward Polaris. Earth’s axis is tilted so that it points toward Polaris over the course of the entire year. Investigation 1: Modeling the Seasons Earth keeps its tilt (Axis pointed towards Polaris) throughout its orbit. In this model, how could we include Earth’s rotation as well as the revolution? Why will this be difficult to model accurately? Where along the orbit would the Northern Hemisphere experience summer? Why? Winter? Why? What season do you think the Northern Hemisphere would be experiencing where you are standing along Earth’s orbit? Why? Now arrange Handout A as shown. We will now model Earth’s revolution by slowly passing Earth counterclockwise from student to student, always making sure that the axis is pointing toward Polaris. Pass Earth along its orbit. Stop when Earth is directly in front of the December Solstice handout. •In December, which hemisphere is tilted toward the sun? the Southern Hemisphere •Which season do you think is just beginning in the Northern Hemisphere? Winter is beginning because the Northern Hemisphere is tilted away from the sun. Look at this heat map diagram of Earth during December. Investigation 1: Modeling the Seasons •What do the colors represent? Red represents more heat. Blue means less heat. Yellow is in-between. •During December, where on Earth are the most intense sun rays hitting? Tropic of Capricorn •Is the Northern or Southern Hemisphere experiencing more concentrated sunlight? In December, the most concentrated sunlight is in the Southern Hemisphere. During December, which hemisphere is probably colder? Why? The Northern Hemisphere is colder because the North Pole is tilted away from the sun’s rays and thus gets less heat. Spin Earth on its axis. Which pole is experiencing longer days? The South Pole is experiencing longer days. In fact, one day in December each year, the South Pole gets 24 hours of sunlight! Investigation 1: Modeling the Seasons Slowly pass Earth counterclockwise along its orbit until it gets to the student standing directly in front of the March Equinox handout. •Which hemisphere (Northern or Southern) is tilted toward the sun? Neither! •Spin Earth on its axis. Which hemisphere do you think is experiencing longer days and shorter nights? The Northern and Southern Hemispheres are receiving equal amounts of light. Investigation 1: Modeling the Seasons Look carefully at this heat map diagram of Earth during the March Equniox. •Which direction is the North Pole tilted here? The North Pole is tilted toward the viewer. The South Pole is tilted away from the viewer. But neither is tilted toward the sun. •Is the Northern or Southern Hemisphere experiencing more concentrated sunlight? The Northern and Southern hemispheres are experiencing the same amounts of concentrated sunlight. Investigation 1: Modeling the Seasons Slowly pass Earth counterclockwise along its orbit until it gets to the student standing directly in front of the June Solstice handout. •Which hemisphere (Northern or Southern) is tilted toward the sun? the Northern Hemisphere •Which season do you think is just beginning in the Northern Hemisphere? Summer is beginning because the Northern Hemisphere is facing toward the sun. Investigation 1: Modeling the Seasons Look at this heat map diagram of Earth during the June Solstice. In June, where are the most intense sun rays hitting? Tropic of Cancer Is the Northern or Southern Hemisphere experiencing more concentrated sunlight? In June, the Northern Hemisphere experiences more concentrated sunlight, as depicted by the heat map. During June, which hemisphere is probably colder? Why? The Southern Hemisphere is colder because the South Pole is tilted away from the sun’s rays and thus gets less heat. Spin Earth on its axis. Which pole is experiencing longer days? The North Pole is experiencing longer days. In fact, one day in June each year, the North Pole gets 24 hours of sunlight! Investigation 1: Modeling the Seasons Slowly pass Earth counterclockwise along its orbit until it gets to the student standing directly in front of the September Equinox handout.
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