Develop and Use Models to Explain How Sunlight Intensity Changes Throughout the Year

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https://en.wikipedia.org/wiki/Axial_tilt

https://en.wikipedia.org/wiki/Axial_tilt

Brief Lesson Descriptions: (Download the free complete lesson plans that include NGSS, student activities, teacher notes, and online resources:how the tilt affects the angle of light and light intenstity lesson plan )   

Lesson 1: How the angle of light affects light intensity

We start off with a question that connects to the previous lesson:  If the North Pole and the South Pole get 24 hours of daylight for 6 months of the year, why aren’t they the hottest places in the world at that time? The following lessons are designed to help answer that question as well as complete the explanation for the seasons.

Students will observe how changing the angle of light changes the amount of energy from that light hitting a single spot. The shallower the angle of light, the more the light energy gets spread out. The steeper the angle of light, the more the energy is concentrated in one spot. Students will conduct an experiment that will measure how the angle (or inclination) at which the light source is viewed can affect the amount of heat received by an object. Students will then observe and model how shadows can help us infer the angle of the light source. Students will predict how this knowledge will help them complete the explanation of the seasons.

Lesson 2: How the shape and tilt of our Earth affects the angle of light from the sun

Students will use a model to compare how the angle of the sun’s light differs when hitting a flat surface and a sphere by observing shadows.  Students will observe how the angle of light from our light bulb sun hits the Earth differently by observing the shadows on the globes that are positioned representing the 2 solstices and 2 equinoxes.  They will observe computer simulation showing how the stick person’s shadow changes throughout the day and the year and construct an explanation as to why the shadow length changes. Students then look at 2 dimensional side view models of Earth at 4 times of the year and draw the angle of light that hits 66 degrees North and South, 23.5 degrees north and south, and the equator and draw conclusions as to why the tropics are always warm while the poles are always cooler no matter how much sunlight they get.

Lesson 3: How the tilt affects the sun’s maximum height throughout the year.

Students use simulations to explore how  the sun’s maximum height changes throughout the year and how that change varies depending on what latitude you are at. They will develop a model to explain why the sun appearing higher and lower in the sky affects the angle of light and the light’s intensity and connect this to the explanation of the seasons. Finally, we put all the pieces of  evidence we gathered since the beginning of the unit and summarize the real reasons for the seasons. Students then complete the post-assessment and a portfolio piece to end the unit.

RESOURCES:

Computer simulations of the seasons: 

Formative Assessment Generator and list of misconceptions:

General video about the seasons:

Video on Solar eclipses, moon phases: 

What a season on Uranus is like:

Credits:

Directions for the models used in the lessons:

  1. Develop a model to observe how Earth’s shape affects the how the angle of light hits different latitudes. Either have these models pre-made (1 per group of 4) or have the students make them.

Directions:

  • Measure and mark a straw into 5 cm pieces. Cut those pieces.

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  • Tape (or adhere in some other way) the pieces so they line up vertically from top to bottom of a file folder. Try to get them straight as possible.
  • Have a light source (flashlight, lightbulb sun model, lamp) placed on a desk or table.
  • Hold the file folder up so that the light source is shining on the file folder. Ask students to observe the shadows of the straws. What do they notice? They should notice that the shadows are relatively the same size.

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  • Then ask students to carefully curve the top and bottom of the file folder to make it more sphere like.

test

Ask students to observe how the size of the shadows changed. How does this model represent what is happening on Earth? (The farther north and south latitudes are from the middle (tropics), the longer the shadow which tells us the light is less intense.) If Earth was flat all latitudes would have the same intensity of light.

 

 

 

 

Directions for globe models:

  1. Copy the sunlight mask for each globe (2 copies total) on transparency. I use this transparency and copy them in a copy machine. The ones in for printer use are a little too thin but it could work also with the straw support. Cut a pair out and tape together. There will be a pair for each globe.43
  2. Starting at one end of a drinking straw, cut a slit about half an inch long. Insert the slit into another drinking straw and tape them together to create a rod just over 15 inches long. This will be the “spine” of the sunlight mask.
  3. Tape the edge of the long strip to the straw rod. Allow about 2 inches of excess transparency to extend past one end of the straw rod.

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  1. Clip a large binder clip to the bottom end of the sunlight mask to act as a stand. Attach the clip so that it forms a stable tripod for holding up the sunlight mask. Adjust the sunlight mask so that it stands up from its base.7 8
  2. Post the mini poster Polaris high up on one wall near the ceiling, if possible. It’s best to put it on a wall that is closest to real North. Tape the A mini poster to the middle of the wall below Polaris. Tape the B, C, and D mini posters to the remaining three walls, moving counterclockwise (as viewed from above) from the A wall, roughly 90 degrees apart from each other. The letter wall will represent different parts of Earth’s orbit in different seasons (the 2 solstices and 2 equinoxes). (The posters can be found attached to the previous lesson)
  1. Place the light bulb sun on a desk in the middle of the room. Tape all wires down. Place 4 more desks approximately 3-4 feet away from the sun model aligning with the mini posters.
  1. Put one globe on each desk, making sure the axis is pointing at Polaris.
  1. Place the sunlight mask in front of the globes.9 11

9. You’ll notice here that the Northern Hemisphere is tilted away from the sun. The sunlight mask’s squares are noticeably crisper near 23.5 degrees S (Tropic of Capricorn) and much more fuzzy the more north you go.  Also, it is fuzzy near the Antarctic Circle even though at this point they are getting 24 hours of sunlight. See the pictures below:

Crisp shadow(intense light) at the Tropic of Capricorn

Crisp shadow(intense light) at the Tropic of Capricorn

Fuzzy shadow (less intense light) at the South Pole

Fuzzy shadow (less intense light) at the South Pole

Students observe these globe models at a summer solstice, winter solstice, and the two equinoxes. I believe it really helps students visualize how the intensity of light changes throughout the year.

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