Key Concepts: Key Vocabulary:

WEATHER AND WATER: Investigation 3: Seasons and Sun

Approximate Timeline: 10 sessions

Standards Addressed: S1 C2 PO1, S1 C2 PO5, S1 C3 PO2, S1 C3 PO3, S1 C3 PO4 S4 C3 PO1

Learning Goals: I will be able to graph and analyze sunlight data. I will be able to model the Earth-Sun relationship while paying particular attention to the rotation, tilt, and revolution.

Extra Resources:

Earth’s axis of rotation tilts at 23.5° and points to the North Star.

The solar angle is the angle that light from the sun strikes Earth’s surface.

Beam spreading is the increase in an area covered by a beam if light as there’s an increase in the solar angle.

Assessments:

Response Sheet: Seasons and Sun End of part 2

Mid-Summative Exam 3

End of investigation

http://vortex.plymouth.edu/sun/sun3.html

Writing Prompt Idea #2: You are a taxpayer in Arizona. The legislature will be voting to fund a new energy plant. Decide which energy source will be the best option for Arizona. Write an editorial persuading the legislature to build this type of energy plant. Choices for energy sources include: wind, dams, fossil fuels, nuclear, or solar. Science: S5 C3 PO1 Writing: S3 C4 PO1

Writing Prompt Idea: You are Copernicus. Write a letter to fellow scientists convincing them that you have the “true” model of the universe. Explain why Ptolemy’s model of the universe with the Earth at the center is false. Include diagrams in your letter. Science: S1 C4 PO1 Writing: S3 C3 PO4; S3 C4 PO1

Fall (autumnal) equinox

Spring (vernal) equinox

Summer solstice

Winter solstice

Solar Angle

Rotation

Seasons and Seasons and SunSun

SUN-EARTH SYSTEMSUN-EARTH SYSTEM

• Turn to this page in your lab books.

READING:READING:“Seasons”“Seasons”

page 17page 17

WORD BANK• Rotation- Earth turning around

on its axis. One rotation=24 hours.

• Revolution- One object moving around another. One Earth revolution around the Sun=365 ¼ days.

• Axis- Imaginary line from North to South pole on which Earth rotates. Tilted at 23.5 degrees.

WORD BANK• Polaris (North Star)- Star directly

over Earth’s North Pole. Always points North.

• Equinox- Day and night hours are equal.–Spring Equinox=March 21–Fall Equinox=September 21

• Summer Solstice- Longest day of the year. June 21

• Winter Solstice- Shortest day of the year. December 21

REVIEWREVIEW• Earth rotates on its axis to produce day

and night.

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

• Summer and Summer Solstice occur when the axis is angled toward the Sun

• Winter and Winter Solstice occur when the axis is angled away from the Sun.

• Seasons are the opposite in the Northern and Southern Hemispheres.

SUMMERSUMMER• What kind of weather do you think of when you hear the season summer?

SUMMERSUMMER• What is it about summer that makes it hotter? What happens to produce more heat?

SUMMERSUMMER• Longer days

result in more time for the Sun’s energy to be absorbed by the land, water, and atmosphere. But is there more to the story?

Summer Video

DEMONSTRATIONDEMONSTRATION• 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 SMARTboard.

• Tracing

LIGHTLIGHT• 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 SMARTboard. Our tracing shows the area that the energy beam covered at two different times.

KEY IDEASKEY IDEAS• The size and shape of the light spot

changes, depending on the angle of shine.

• 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.

ENERGY!!!ENERGY!!!• 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 density.

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

• When few rays hit an area, energy density is low.

ENERGY!!!ENERGY!!!• The flashlight puts out a steady beam of

light rays that is about 5cm across. When the light beam falls on a surface from directly above (90 degrees), the area it covers is a circle about 20cm2.

• When the angle that the light is coming from changes from 90 to 15 degrees, the beam falls on an oval surface about 60cm2.

• The amount of light in the flashlight beam does not change. All that changes is the angle at which the light strikes the surface.

SOLAR ANGLESOLAR ANGLE

• Turn and face the whiteboard.

SOLAR ANGLESOLAR ANGLE• 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 degrees.

• Light rays shining from directly overhead have a high solar angle. These are hitting Earth’s surface at 90 degrees.

SOLAR ANGLESOLAR ANGLE• Notice that the incoming rays of light

are equally spaced in both beams. But because of the solar angle, three times as many rays are falling on Earth when the light comes from a high solar angle.

• Therefore, the density of energy is greatest when light shines on a surface at a 90 degree angle.

BEAM SPREADINGBEAM SPREADING• The way a light beam covers a larger

area when it hits a surface at an angle is called beam spreading.

• Think about this. If you spread some jam evenly on a cracker and the same amount of jam evenly on a slice of bread, the jam will be thicker on the cracker than on the bread.

• You will get more jam with each bite of cracker than with each bite of bread.

DEMONSTRATIONDEMONSTRATION• Sunlight travels 150 million

kilometers in absolutely straight lines and uniform density to get to Earth.

• We can look at how light spreads when it hits Earth’s surface by masking all of the light except for one column of rays by putting a barrier with a hole between Earth and the Sun.

DEMONSTRATIONDEMONSTRATION• When the beam of light hits different

parts of the globe, what shape is it?• What time of day is the solar energy

most intense?– Noon, when the Sun is at a high (large)

solar angle

• Least intense?– Sunrise and sunset, when the solar

angle is low and the energy spreads over a large area

DEMONSTRATIONDEMONSTRATION• What regions of the planet are

subjected to the most intense solar radiation?– Near the equator

• Least intense?– North and South polar regions

SOLAR ANGLE ON SOLAR ANGLE ON EARTHEARTH

• Turn and face the white board.

SOLAR ANGLESOLAR ANGLE• Because Earth is round, the angle at

which light hits it is different from place to place. Light does not come to Earth from different angles; light strikes surfaces that are at different angles. 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.

SOLAR ANGLESOLAR ANGLE• In this illustration we see four rays of light

coming to Earth. Ray 1 happened to strike Earth exactly perpendicular to the surface. The solar angle is 90 degrees.

• Light ray 2, however, did not strike perpendicular to the surface because the surface is farther north. The solar angle, when compared to Earth’s surface, is about 60 degrees.

• Light ray 3 and 4 hit the surface at even smaller angles, perhaps 45 and 30 degrees.

SUNLIGHT ON SUNLIGHT ON EARTH’S SURFACEEARTH’S SURFACE

• Turn to this page in your lab books.

SOLAR ANGLE AND SOLAR ANGLE AND SOLAR ENERGYSOLAR ENERGY

• The greater the solar angle, the greater the density of radiant energy.

• Solar energy is most intense during the middle of the day.

• Solar energy is most intense near the equator.

• Energy is least intense in the morning and evening.

• Energy is least intense at the polar regions.

WORD BANK

• Solar Angle- The angle at which light strikes a surface. Greater the angle (90 degrees), the greater the energy.

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