Sun and Earth

Extreme-ultraviolet observation of the full Sun showing bright active regions, displayed in yellow. — SDO's Atmospheric Imaging Assembly, 18 December 2015. This false-colour ultraviolet observation reveals the hot solar atmosphere, not the Sun's visible colour.

A suggested lesson sequence

Use these stages at your own pace. Pause for students to sketch, compare observations or lead part of the demonstration.

01
Observe
At zero declination compare the equator, 60° and a pole.
Open Observe
02
Tinker
Change declination to each solstice limit and compare noon with daily mean.
Open Tinker
03
Explain
Why can two places receive different amounts of solar energy even on the same day?
Open Explain
04
Check
Choose an answer and explain your reasoning. Each question includes feedback.
Open Check

Rehearse with the model

The same scene and controls as the lab. Load it when you are ready; use Start projector for the full classroom view.

Before the lesson

Explain how latitude and the Sun’s declination affect the solar energy received at noon and across a whole day.

Open the model before the lesson and choose a view that makes the important feature easy to see. Drag to rotate, and use the on-screen controls to change one variable at a time. The Controls panel explains the available keyboard shortcuts.

Ask students to predict the result before you change a setting. Compare the new view with the starting state.

Guide the demonstration

At zero declination compare the equator, 60° and a pole.

Change declination to each solstice limit and compare noon with daily mean.

Discuss a common misconception

“Sunlight above the atmosphere supplies the same energy to every square metre of ground.” The angle of the rays changes how incoming energy is spread over a horizontal surface. At a lower Sun angle the same beam covers more ground, and day length also changes daily energy receipt. Clouds, reflection and atmospheric absorption further modify the energy reaching the surface.

Build the explanation

The same sunlight spreads across a larger area when it strikes a surface at a shallow angle. Latitude, solar declination and day length therefore affect the energy received by a horizontal surface.

Change declination to each solstice limit and compare noon with daily mean.

The calculation describes sunlight above the atmosphere; clouds and atmospheric absorption would change the energy reaching the ground.

Teaching notes

Distinguish sunlight measured perpendicular to a beam from energy received by a horizontal surface.

Include the night-time interval when interpreting a daily average of incoming solar energy.

Explain the seasons through Earth’s axial tilt rather than changes in visible sunspots.

Check understanding

Open Check for 4 questions. Ask students to explain their choice before revealing the answer.

Return to the opening photograph. Ask students to identify one visible feature and explain which part of the model helps account for it.

Look more closely

Use these observations to connect the vocabulary to features students can identify.

Solar constant

An SDO observation of the solar photosphere showing a large dark sunspot group. — NASA SDO observes the solar photosphere and sunspots. The Sun supplies incoming solar radiation (insolation). The solar constant is irradiance near 1 AU on a plane perpendicular to the rays, about 1,361 W m⁻²; it is not measured by this visible-light photograph.

Read the definition

Incidence

Orange and blue atmospheric layers above Earth's curved horizon, with a crescent Moon in the black sky. — Sunlight passing through Earth's atmospheric limb in an ISS photograph. At low solar angles, light crosses a longer atmospheric path and spreads across a larger surface area.