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. Which hemisphere (Northern or Southern) is tilted toward the sun? Neither! Which season is just beginning in the Northern Hemisphere? How do you know? Autumn is just beginning. The September Equinox is the first day of autumn. Look at this heat map diagram of Investigation 1: Modeling the Seasons Earth during the September Equinox. Which direction is the North Pole tilted here? The North Pole is tilted away from the viewer. The South Pole is tilted toward the viewer. But neither is tilted toward the sun. Is the Northern or Southern Hemisphere experiencing more concentrated sunlight? Finally, pass Earth counterclockwise back to the December Solstice. The Northern and Southern Finally, pass Earth counterclockwise back to the December hemispheres are experiencing the Solstice. same amounts of concentrated sunlight. Read p25-26 (Sec March or 2 Earth’s shape December and the sun’s September energy)

June March or September 2. Earth's Shape and the Sun's Energy (p24)

The sunlight that warms you also carries energy that warms Earth. Light does not strike all parts of Earth in the same way.

2 factors that affect heat/energy/light on Earth • Uneven Heating and the Angle of the Sun’s Light: • Earth’s Shape and the Angle of the Sun’s light: 2. Earth's Shape and the Sun's Energy (p24) Uneven Heating and the Angle of the Sun’s Light: The angle at which sunlight strikes Earth determines how concentrated the light is. Sunlight is more concentrated when it hits the Earth perpendicularly than when it hits it at a larger angle. How concentrated the light is determines how much a spot on Earth is heated. When sunlight transfers more energy to the surface of Earth, it is heated more. As a result, some locations on Earth are always colder than other locations. 2. Earth's Shape and the Sun's Energy (p25) Earth’s Shape and the Angle of the Sun’s light: Earth is a sphere, so it does not have a flat surface. Therefore, sunlight always hits different parts of Earth at different angles. Near the equator, sunlight strikes Earth nearly perpendicularly and transfers a lot of energy to that part of Earth’s surface. North/South of the equator, sunlight strikes at a larger angle, and less energy is transferred to that part of Earth’s surface. The same amount of incoming energy is spread over a larger and larger area the farther away you move from the equator. 2. Earth's Shape and the Sun's Energy (p25) Students develop a model to measure light on Earth’s surface at different latitudes during different seasons. Inv.2 Measuring Energy on Earth’s Surface • You now know that Earth’s tilt causes seasons. Different parts of Earth receive different concentrations of sunlight depending on Earth’s tilt relative to the sun. • Discuss with your partner: How does Earth’s tilted axis affect how sunlight energy is distributed on Earth? Inv.2 Measuring Energy on Earth’s Surface • First, let’s examine this diagram: Colder • Where is the sun relative to Earth? The sun must be to the left of Earth. • Where are the most intense light rays hitting? At what angle do they hit Earth? At the equator. 90 degrees. • Which part of Earth is hotter? Which part is colder? Why? The equator is hotter than the Poles because the light is more concentrated. hotter • Can this image represent either December or June? No, because neither hemisphere is tilted toward the sun. This might be either the March Equinox or September Equinox. Inv.2 Measuring Energy on Earth’s Surface

Measuring with a Flashlight and Globe Now try to measure solar energy using a flashlight and an inflatable Earth. The flashlight will represent light rays coming from the sun. For this demonstration, two students are needed to assist in the modeling. Hold the flashlight parallel to the ground. Shine it on the equator. Then shine it on Alaska. Keep the flashlight parallel to the ground! (hint….tilt the Earth) Inv.2 Measuring Energy on Earth’s Surface Conduct a science talk about this model: • What do you observe about the area where the light shines on Earth? The light is brighter (less spread out) on the equator and dimmer (more spread out) on Alaska. • Does the equator or Alaska receive more intense solar energy? The equator must receive more intense solar energy. • Can you use this model to measure the difference between the concentration of light at different places? Not really. You can only see where the light is more or less spread out. • Why is it difficult to measure the light concentration on a three-dimensional globe? The curved surface makes it hard to show where the light is actually hitting. Inv.2 Measuring Energy on Earth’s Surface Let’s improve the model to measure and compare the intensity of sunlight at different locations each season. What similarities do you see between these two models? • What differences do you see? Light is hitting each surface at 90 and 135 degrees.

The first image shows light hitting a flat surface instead of the spherical Earth. Inv.2 Measuring Energy on Earth’s Surface Measuring with a Flashlight and Grid Paper ❑You will use a flashlight and grid paper to represent a ray of sunlight and Earth. ❑Remember that Earth maintains a nearly constant distance from the sun, so you will always keep the grid paper the same distance from the flashlight! ❑Your goal will be to measure how sunlight intensity varies at different areas on Earth. ❑You will do this by counting the number of squares that are illuminated by the flashlight. Inv.2 Measuring Energy on Earth’s Surface Look at the image to the right. Each flashlight is producing equal amounts of light. • How many squares are illuminated on Paper A? On Paper B? Paper A has about 8 squares illuminated. Paper B has about 6 squares illuminated. • Is the light more spread out on Paper A or Paper B? The light is spread across more squares on Paper A. • So which paper is receiving more concentrated sunlight? Paper B. Because the light is in fewer squares, each square must be getting more intense light. Therefore, “more squares” equals “less intense light.” Inv.2 Measuring Energy on Earth’s Surface Before you collect data, make a prediction about which location (latitude) on Earth experiences the most direct sunlight at each time of year. In the table below, in the Prediction column, write the latitude where you think sunlight will be the most concentrated for each time of the year.

Equator Tropic of Cancer Tropic of Capricorn Inv.2 Measuring Energy on Earth’s Surface • Get into groups of four. • Each group needs the following materials: • grid paper • pen or pencil • string (10 cm) • flashlight • tape • protractor Follow these steps to set up the model: • Use a pen to punch a hole in the center of the grid paper. • Use the 10 cm string to attach the grid paper to your flashlight. • Always keep the flashlight in the exact same location. Use the protractor to hold the grid paper at various angles. Try holding it at 90 degrees now! Inv.2 Measuring Energy on Earth’s Surface

Complete the following steps for each of the locations shown in the December Solstice, March Equinox, June Solstice, and September Equinox diagrams. • Hold the grid paper at the sun’s angle for each location. • Trace the outline of the inner circle of light on the grid. – USE A DRY ERASE MARKER ONLY • Count the squares the inner circle of light covers. • Record this data on your data table. Inv.2 Measuring Energy on Earth’s Surface

15 12 9 Inv.2 Measuring Energy on Earth’s Surface

15 12 9 12 9 12 Inv.2 Measuring Energy on Earth’s Surface

15 12 9 12 9 12 9 12 15 Inv.2 Measuring Energy on Earth’s Surface

Complete the following steps for each of the locations shown in the December Solstice, March Equinox, June Solstice, and September Equinox diagrams. • Hold the grid paper at the sun’s angle for each location. • Trace the outline of the inner circle of light on the grid. • – USE A DRY ERASE MARKER ONLY • Count the squares the inner circle of light covers. • Record this data on your data table. Inv.2 Measuring Energy on Earth’s Surface

15 12 9 12 9 12 9 12 15 12 9 12 Inv.2 Measuring Energy on Earth’s Surface 3) If the sun emits equal amounts of light in all directions, what conclusions can you draw about the intensity of the light on areas where sunlight is spread over more squares compared to areas where sunlight is spread over less squares? When the sunlight hits more squares on the grid paper, that means that the light is spread out over a bigger distance. So the light is less concentrated or diffused.

When the sunlight hits a smaller number of squares, it means that the light is more concentrated in one area. So the light is more intense. Inv.2 Measuring Energy on Earth’s Surface 4) How do the patterns in your data help explain why seasons occur? The data shows that the equator receives the most direct sunlight (because it is the most concentrated in a few squares) during the equinoxes The tropics receive the most direct sunlight during the solstices. Areas with more concentrated light have more solar energy reaching Earth’s surface, thus higher temperatures, or summer. Sec 1. The Seasons & Sec 2. Earth's Shape and the Sun's Energy Review

1. Describe the seasonal patterns that you have observed where you live.

2. Earth is unevenly heated. On this image of Earth, label where the most concentrated sunlight hits Earth. Also, label where the least concentrated sunlight. least concentrated sunlight hits Earth. most concentrated sunlight 3. Use your knowledge about sunlight and energy to explain why the climate is warmer near Earth’s equator and colder near the poles. Use the terms light, angle, concentrated, and diffuse in your response. Equator - 90o - sunlight is more concentrated - more energy is transferred - Temperature rises. Poles - > 90o - sunlight is more diffuse- less energy is transferred – Temperature Lower 4. Recall that the Earth is tilted. (In the image above, Earth is tilted toward the viewer.) Sometimes the Northern Hemisphere is tilted toward the sun, other times the Southern Hemisphere is tilted toward the sun. Predict how this affects temperature variation on Earth. The Earth’s tilt will result in concentrated sunlight hitting other parts of the Earth besides the equator. More concentrated sunlight = higher temperatures Least concentrated sunlight = lower temperatures https://www.e-education.psu.edu/emsc100tsb/node/227 Inv.2 Measuring Energy on Earth’s Surface 3. Earth’s Tilted Axis and the Seasons A system is a set of connected parts that form a complex whole. • Earth and the sun work as parts of a system to produce seasons on Earth. • Earth's round surface results in warmer climates at the equator and colder climates near the poles. Earth's tilted axis causes different latitudes to receive more or less concentrated sunlight during different points of a year. 3. Earth’s Tilted Axis and the Seasons 4. The Solstices A solstice is a time of the year when the North or South Pole is closest to the sun during noon. During a solstice, the sun directly hits one of the tropics. The tropics are the latitudes furthest north and south that receive direct sunlight. Tropic of Cancer, located at 23.5°N, Tropic of Capricorn, located at 23.5°S. June Solstice 4. The Solstices December Solstice

• Sunlight hits the Tropic of Cancer in the • Sunlight hits the Tropic of Capricorn in the Northern Hemisphere perpendicularly at Southern Hemisphere perpendicularly at 90°. 90°. • The December Solstice is the day of the year • The June Solstice is the day of the year that where the Southern Hemisphere receives the the Northern Hemisphere receives the most most energy form the sun and the Northern energy from the sun, and the Southern Hemisphere receives the least energy. Hemisphere experiences the least. • The December Solstice marks the first day of • marks the first day of summer for the winter for the Northern Hemisphere, and the Northern Hemisphere, and the first day of first day of summer for the Southern winter for the Southern Hemisphere. Hemisphere. 5. The Equinoxes When the North and South Pole are an equal distance from the sun, the latitude that receives the most energy from the sun is 0° latitude, or the equator. An equinox is a time of the year when the sun is directly overhead at the equator during noon. Places on the equator experience sunlight at a 90° angle. (perpendicular) September Equinox 5. The Equinoxes March Equinox • Btn June and December solstice • Btn December and June solstice The latitudes closer to the equator receive more and more concentrated sunlight until the equator, or 0° latitude, receives sunlight at a perpendicular angle. The September The March Equinox Equinox marks the first marks the first day of day of autumn in the spring for the Northern Hemisphere, Northern and the first day of Hemisphere, and the spring in the Southern first day of autumn Hemisphere. for the Southern Hemisphere.

Sec 3. Earth's Tilted Axis and the Seasons_ Sec 4. The Solstices_ Sec 5. The Equinoxes Review

1) Provide an explanation for why this system results in the uneven heating on Earth. When N or S hemisphere is facing towards the sun = more direct sunlight & energy (summer). When Nor S hemisphere is facing away from the sun = less direct sunlight & energy (winter).

2) Suppose Earth’s axis was not tilted. What would be the effect of this on temperature variation? If Earth’s axis did not tilt, the most concentrated sunlight would always hit the same part of Earth and there would be no seasons. Temperature would be constant throughout the year. 3. On this image of Earth, draw and label the Tropic of Cancer and the Tropic of Capricorn.

4. Which solstice is Earth experiencing in this image?

December Solstice. Sec 3. Earth's Tilted Axis and the Seasons_ Sec 4. The Solstices_ Sec 5. The Equinoxes Review

5. Summer is about to begin for your friend in South America, while you are preparing for winter. Explain to your friend why you experience opposite seasons. When Earth’s South Pole is tilted to the sun then summer is starting in the Southern Hemisphere. This means that the North Pole is tilted away from the sun, is receiving less sunlight, and winter is starting.

6. Complete the table below. June Solstice December Solstice Which pole is tilted towards the sun? The sun is directly overhead which tropic? Which season is starting for the Northern Hemisphere? Sec 3. Earth's Tilted Axis and the Seasons_ Sec 4. The Solstices_ Sec 5. The Equinoxes Review

7. The word “equinox” comes from Latin and means “equal night.” Explain how all parts of the Earth receive 12 hours of daylight and 12 hours of darkness on these two days of the year. When the most direct sunlight (90O) is hitting the equator, then the Northern and Southern Hemispheres are receiving equal amounts of sunlight. The 24-hour day is divided in half between night and day, all over the Earth.

8. Complete the table below. September Equinox March Equinox Which pole is tilted towards the sun?

Which season is starting for the Northern Hemisphere? 6. The Seasons and the Sun’s Path in the Sky The height of the sun and amount of time the sun is visible in the sky each day changes throughout the year. These effects are caused by the tilt of Earth's axis relative to the sun. The location of sunrise and sunset also changes with the seasons. The sun does not rise exactly in the east and set exactly in the west. Instead, in the Northern Hemisphere, the sun rises toward the southeast in the winter and rises toward the northeast in the summer. 6. The Seasons and the Sun’s Path in the Sky Time- Lapse Sunrise and Sunset Times for the 22nd of each month of 2018 in Peoria, Illinois Sunrise and Sunset Times for the 22nd of each month of 2018 in Peoria, Illinois

24:00 23:00 June Solstice Sunrise Sunset 22:00 Month 21:00 March Equinox Sept. Equinox AM PM 20:00 Jan 7:14 17:00 19:00 Feb 6:51 17:38 18:00 December Solstice Mar 6:45 19:09 17:00 Apr 6:07 19:42 16:00 May 5:32 20:12 15:00 June 5:24 20:31 14:00 July 5:43 20:21 13:00 Aug 6:12 19:45 12:00 Time (military) Time 11:00 Sept 6:43 18:54 10:00 Oct 7:01 18:06 9:00 Nov 7:08 16:33 8:00 Dec 7:17 16:31 7:00 6:00 5:00 Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Months of the Year Sunrise and Sunset Times for the 22nd of each month of 2018 in Peoria, Illinois Months of the Year 21:36

19:12

16:48

14:24

12:00

Fall spring

9:36

Summer Solstice Summer

Time (military) Time

March equinox March Winter Solstice Winter

7:12 equinox September

4:48

2:24

0:00 Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec

Sunrise AM Sunset PM Ancient people also used calendars to determine the start of each season. But their calendars were unlike calendars you might use today. Ancient civilizations built large structures that tracked the motion of the sun.

7. Calendars of Ancient Civilizations • At the top of a hill in the coastal desert 7. Calendars of of Peru lies 13 towers in a perfect line. • The sun perfectly aligns with corresponding Ancient Civilizations towers during the solstices and equinoxes. • Built by ancient Egyptians in 2000 BCE • The temple is the largest complex in the world • during the solstices, the sun’s rays run through the length 7. Calendars of Ancient of the temple and into the room the Civilizations farthest in. • Stonehenge was designed by people who lived more than 3,000 years ago in what is now England. • The structure was built using huge rocks arranged in a circle. • When you stand inside the circle at different times of the year, the rising sun appears near different rocks. What causes the sunrise to appear near different rocks at different times of the year? The sun’s path in the sky begins 7. Calendars of Ancient and ends in slightly different Civilizations places during the year.