1. Investigation 3 Part 1
Seasons

2. Quick write What causes seasons on Earth? Update Moon Log
Take a few moments to have a student update the class Moon Log and remind students to keep up with their daily observations.
2. Assign quick write
What causes seasons on Earth?
WHAT TO LOOK FOR:
Earth’s orbit around the Sun takes about 365 days and is nearly circular.
Earth’s axis is tilted 23.5° and points toward the North Star as Earth revolved around the Sun.
In summer, the northern end of the axis is tipped toward the Sun; in winter, the northern end of the axis is tipped away from the Sun.
When neither end of the axis is tipped toward the Sun, it is either spring or fall.
Energy is more concentrated in areas that receive sunlight at a high solar angle and less concentrated in areas that receive sunlight at a low solar angle.
In summer, daylight is longer, and the area receives sunlight at a high solar angle, so it is warmer. In winter, daylight is shorter, and the area receives sunlight at a low solar angle, so it is cooler.

3. How do you know when it’s summer?
Identify seasons
Tell students,
“Okay, that was kind of a hard question. Let’s start with an easier one.”
Answers will vary.
Confirm that hotter weather and longer days are indications of summer. Tell students,
“Heat and more hours of daylight are not just signs that summer is here; they also can help us understand the reasons why we have seasons on Earth. We’ll start by looking at the issue of heat.

4. Focus question Why is it hotter in the summer?
5. Discuss summer heat
Ask students to talk in their groups for 1 minute to generate reasons for summer being hotter. Then call on Reporters to offer their ideas. Students often suggest that the longer daylight hours of summer provide more time for things to heat up. Tell students,
“Longer daylight results in more time for the Sun’s heat (energy) to be absorbed by the land, water, and atmosphere. Longer days can make it hotter. However, the longest daylight in the summer in the Northern Hemisphere is in Canada and Alaska, and the hottest summer days are in the southern United States and Mexico. There must be more to the story.”
TEACHING NOTE:
Some students may suggest that summer days are hotter because Earth is closer to the Sun. This is a common misconception that will be addressed more directly when students construct a scale model of the solar system later in the course. For now, if students share this idea, remind them that Earth’s orbit is nearly circular, so distance from the Sun is not a factor.

5. demonstration Flashlight beam represents a beam of light from the sun.
Observe where it hits the floor
We will trace it from directly above and at an angle.
6. Demonstrate light on a surface
Get your flashlight and meterstick setup. Dim the room lights. Tell students,
“I am going to use this flashlight beam to represent a beam of light from the Sun. Observe the spot of light where the beam hits the floor.”
Shine the beam straight down at the floor, and slowly tip the system sideways, so the beam intersects the floor at a steadily declining angle. Repeat the process several times.
7. Circle the light spots
To emphasize the effect of beam spreading, put a piece of chart paper on the floor, shine the light straight down, and have a student trace the light spot. Repeat the process with the light shining at an angle.

6. Light as energy
How do you explain the different shapes of the light spots?
When is the area of the spot largest?
Which spot delivers the greatest amount of energy to the floor?
8. Introduce light as energy
Tell students,
“Light is a form of energy. This flashlight and the Sun are both sources of light energy. I used this flashlight to shine light energy on the floor. This paper shows the area that the energy beam covered at two different times.”
Distribute a copy of notebook sheet 8, Beam Spreading, to each student. Tell students,
“Discuss the demonstration in your groups. Work together to write answers to the first three questions on your notebook sheets.”

7. Beam spreading
The size and shape of the light spot changes, depending on the angle of the beam.
The light spot gets bigger as the angle between the beam of light and the floor gets smaller.
The amount of light energy in the beam stays the same, so both light spots deliver the same amount of energy to the paper.
9. Introduce beam spreading
Ask students to share the ideas discussed in their groups. Reinforce these observations.
TEACHING NOTE:
The last bullet point is the most important finding of this demonstration.
Tell students,
“Energy travels from the Sun to Earth as radiation. Radiant energy travels in rays. The number of rays hitting a given area is the energy concentration. When lots of rays hit an area, energy concentration is high. When few rays hit an area, energy concentration is low.”
Use the flashlight on the stick to model as you explain the following:
“The flashlight puts out a steady beam of light rays that is about 5 cm across. When the light beam falls on a surface from directly above (90°), the area it covers is a circle about 20 cm².

8. Beam spreading
When the angle that the light is coming from changes from 90° to 15°, what happens to the size of the area the beam falls on?
Does the amount of light in the flashlight beam change?
9. Continued
Ask questions on board.
Answers:
The area is oval, not round; the beam falls on a larger surface area; it’s about three times as large, about 60 cm².
No.

9. 9. Continued
Project teacher master B, Solar Angle (on slide), and continue.
“The angle at which light strikes a surface is called solar angle. These low solar-angle rays are hitting Earth’s surface at about 15° (Top image). These light rays shining from directly overhead have a high solar angle. They are hitting Earth’s surface at 90° (Bottom image). The incoming rays of light are equally spaced in both beams, but because of the difference in the angle of the Sun, three times as many rays are falling on a particular patch of Earth when the light comes from a high solar angle. The concentration of energy is greatest when light shines on a surface at a 90° angle.”
“The way a light beam covers a larger area when it hits a surface at an angle is called beam spreading. Think about this. When you take a spoonful of jam and put it on a piece of bread, it’s all concentrated in one area. If you took a bite of that area, you’d get a lot of jam! When you spread the jam around evenly, it is still the same total amount of jam. If you took one bite of the bread, the jam would be a lot less concentrated.”

10. Penny question You have about 6 minutes to work on questions 4-6.
10. Record vocabulary
11. Answer the penny question
Ask students to turn their attention to questions 4-6 on notebook sheet 8, Beam Spreading. Give them 6 minutes to write their answers.
Students should understand that the solar angle determines the energy concentration – the amount of energy per unit of surface area. Since the surface area of a penny does not change, the amount of energy hitting it varies with the solar angle. The greater the solar angle, the more energy the penny will receive.
This means that the penny would get hottest with a heat lamp at a high solar angle. For the same reason, high solar angles result in more surface heating by the sunlight on the surface of Earth.
---POSSIBLE BREAKPOINT---

11. demonstration 12. Demonstrate beam spreading on a globe
Bring your globe forward. Tell students,
“This is a model of Earth. Sunlight travels about 150 million kilometers to reach Earth. Since the Sun is so far away, the beams that hit Earth are in straight lines and equally concentrated. We can look at how light spreads when it hits Earth’s surface by masking all the light except for one column of rays. We’ll put a barrier with a hole between Earth and the Sun.”
Set up the demonstration and ask a couple of students to help you.
Aim the projector into the room. This is the sun.
Position the globe in the flood of light, 3-5 m from the projector. Dim the room lights.
Hold the sheet of cardboard with the hole about 1 meter from the globe, allowing light to shine through the hole onto the globe. Start with the beam of light near the equator so the beam is fairly round.
Move the beam of light to various positions on the globe to show the effects of beam spreading.
Ask a student to describe the shapes of the light beams to the rest of the class. Let students come up in groups to move the cardboard sheet around and observe the beam-spreading effect as the beam is directed high on the globe (far north) and to the sides of the globe (morning and evening). If the globe has a plastic finish, students can outline a few circles using a wet-erase pen.

12. questions
When the beam of light hits the globe near the center of the equator, what shape is the light?
When the beam of light hits the right or left side of the globe near the equator, what shape is the light?
When the beam of light hits the globe a little bit north or south of the equator, what shape is the spot of light?
When the beam of light hits the globe near the poles, what shape is the spot of light?
13. Discuss the globe demonstration
While you move the beam of light around on the globe, ask the questions on slide.
Answers:
Round.
A long oval.
Slightly oval.

13. More questions What time of day is the solar energy most concentrated?
What time of day is the solar energy least concentrated?
What regions of the planet are subjected to the most concentrated and least concentrated solar radiation?
13. Continued
Answers:
Noon, when the Sun is at a high (large) solar angle.
Sunrise and sunset, when the solar angle is low and the energy spreads over a large area.
Most concentrated in the tropics near the equator; least concentrated in the north and south polar regions.

14. 14. Reinforce solar angle
Project teacher master C, Solar Angle on Earth (left image). Tell students,
“Since Earth is round, the angle at which light hits Earth is different from place to place. Light does not come to Earth from different angles; light strikes surfaces that are at different angles. Remember, the angle between the incoming rays of light and the surface of the land is the solar angle. We can see this if we think of Earth’s surface as made of lots of little, flat areas.”
“In this illustration, we see four rays of light coming to Earth. Ray 1 happens to strike Earth exactly perpendicular to the surface. The solar angle is 90°.”
“Light ray 2, however, does not strike perpendicular to the surface because the surface is farther north. The solar angle, when compared to Earth’s surface, is about 60°. Light rays 3 and 4 strike the surface at even smaller angles, perhaps 45° and 30°.”
Project teacher master D, Sunlight on Earth’s Surface (right image). Point out that light energy from the Sun is distributed over a larger area when it hits Earth’s surface at an angle. The beam spreads more and more the farther north or south you go.
“Beam spreading does the same thing as you move east and west. In the morning and evening, the solar angle is low, so the beam spreading is large. In the middle of the day, the Sun’s energy is most concentrated because the Sun is overhead at a high solar angle.”

15. Answer the Focus question
Why is it hotter in the summer?
Discuss with group
Will share as a class
15. Answer the focus question
Tell students,
“The greater the solar angle, the greater the concentration of radiant energy. Light shining from directly above is most intense; light coming at an angle is less concentrated.”
“Almost all the energy coming to Earth is solar energy. Light absorbed by the land, water, and air is converted to heat.”
Ask students to talk in their groups to discuss the focus question for this part.
Why is it hotter in the summer?
Call on each group to offer its ideas about solar energy and Earth heating. Summarize and focus their ideas after the discussion.
Areas where the Sun shines directly down on Earth receive more intense energy than areas that experience beam spreading.
The greater the amount of energy absorbed, the hotter the area becomes.
Sine Earth’s axis is tilted at 23.5° and the Northern Hemisphere leans toward the Sun in the summer, our town receives more intense solar energy in the summer months.
Ask students to work alone to record final answers to the focus question

16. Answer each to the best of your ability using Claim, Evidence, and Reasoning on a SEPARATE sheet of paper.
16. Assess progress: response sheet
Distribute notebook sheet 9, Response Sheet – Investigation 3. Assign as homework or as an in-class assignment. Students should work individually to respond to the items on the back of their sheets or on separate sheets of paper, not directly in their notebooks, so you can collect the sheets when they are finished. Students will self-assess their work on this sheet in Part 2.
TEACHING NOTE: If given as homework, mark completion based on whether students attempted to respond to each item. Students are still developing their understanding of seasons at this point.
WHAT TO LOOK FOR:
Earth’s orbit around the Sun takes about 365 days and is nearly circular.
Earth’s axis is tilted 23.5° and always points toward the North Star as Earth revolves around the Sun.
In summer, the axis is tipped toward the Sun; in winter, the axis is tipped away from the Sun.
Summer is hotter because days are longer, and light is more concentrated due to less beam spreading.
The four changes of season are marked by summer solstice (the longest day of the year in the Northern Hemisphere – June 20 or 21), fall equinox (September 22 or 23), winter solstice (December 21 or 22), and spring equinox (March 20 or 21).
17. Review vocabulary