# Seasons and Sun - PowerPoint PPT Presentation

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Seasons and Sun. Sun Angle and Solar Heating Investigation 3, Part 3. Lesson Objective: I can explain how beam spreading affects the temperature of the Earth in different locations. The tilt of Earth’s axis produces changes in day length over the course of a year. Review.

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Seasons and Sun

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## Seasons and Sun

Sun Angle and Solar Heating

Investigation 3, Part 3

### Lesson Objective:I can explain how beam spreading affects the temperature of the Earth in different locations.

The tilt of Earth’s axis produces changes in day length over the course of a year

### Review

Earth rotates on its axis to produce day and night

### Questions-.

• What kind of weather do you generally associate with summer?

• What is it about summer that makes it hotter?

• What happens to produce more heat?

• Longer days means

more time for the Sun’s energy to be absorbed by the:

• Land

• Water

• Atmosphere

• Maybe that’s why it’s hotter???

But could there be more to this story?

Circle the brightest spot on the graph paper

### Light Model

Observe the spot of light where the beam hits the floor

To represent a beam of light from the Sun

Form of energy

The circles show the area that the energy beam covered at two different times.

Light

Both are sources of light energy.

• Discuss the demonstration/lab in your group.

Size and shape of the light spot changes, depending on the angle.

### Observations

Spot gets bigger as the angle between the beam of light and floor gets smaller.

• Amount of light energy in the beam stays the same.

• Both spots deliver the same amount of energy to the paper.

### Light Energy-Add notes to ISN.

Energy travels from the Sun to Earth as radiation, or solar energy. Heat is transferred to the Earth by radiation.

### Solar Angle-

Angle at which light strikes a surface (add definition to ISN)

Light rays from directly overhead have a high solar angle.

Low solar angle rays hit the Earth’s surface at about 15˚.

### Think of it like this:

• If you spread jelly evenly on a cracker and the same amount of jelly on a piece of bread, the jelly on the cracker will be thicker than the jelly on the piece of bread. You will get more jelly with each bite of cracker than with the piece of bread.

When fewer rays hit an area, the energy density is low. Not as much energy is transferred to that part of the Earth.

### Energy Density-

Number of rays hitting a given area is the energy density. (add definition to ISN and draw a picture of this example)

When lots of rays hit an area, the energy density is high.

Notice rays are equally spaced in both beams,

but because of solar angle,

there are three times as many rays when it is from a high solar angle.

• The way a light beam covers a larger area when it hits a surface at an angle

• Even though, the same amount of energy is hitting the surface, it is more dense, more intense when coming from directly overhead. The higher the angle, the more intense solar energy.

### Penny Question

90˚

30˚

Amount of energy hitting it varies with the solar angle

Surface area of a penny does not change

90˚

30˚

The greater the angle, the greater the energy it will receive.

### Solar Angle and Earth

Earth is round = the angle at which light hits it is different from place to place

Sunlight

Earth viewed as many flat surfaces

Light strikes surfaces that are at different angles.

### Solar Angle on Earth

30˚

Angle between the incoming rays of light and the surface of the land is the solar angle.

45˚

Solar angle = 60˚

Solar angle = 90˚

### Sunlight on Earth’s Surface

Light energy from the Sun is distributed over a larger area when it hits Earth’s surface at an angle.

Beam spreads more and more the farther north or south your go.

Does the same thing if you move east and west

### Afternoon Sun

Energy is most intense

High solar angleBeam spreading is small, the angle is 90 degrees at noon, so that is the most intense time of day

### Morning and Evening Sun

Energy is least intense

Low solar angleBeam spreading is large

### The Results

Solar energy is most intense during the middle of the day in the tropics.

Energy is least intense in the morning, evening and extreme north and south regions.

### Solar Energy-Take NOTES in ISN!

• Almost all of the energy coming to Earth is solar energy.

• Light absorbed by the land, water, and air is converted to heat.

• Heat is the form of energy that makes things happen in the atmosphere.

### Summary

• Areas of the planet where solar radiation shines direction down on Earth are subjected to more intense energy than areas that experience beam spreading. The great the amount of energy absorbed, the hotter the area becomes. This is why the hottest part of Earth is in the region of the tropics (near the equator).

### Why is summer hotter than winter?

• Because the Earth’s axis is tilted, the Northern Hemisphere received more intense solar energy in the summer months, making summer HOTTER!

• During the winter months, sunlight strikes the Northern Hemisphere at a low solar angle, resulting in less heating from solar radiation, making it COOLER!