Tides

A fishing boat rests on exposed mud beside a wharf at low tide in Nova Scotia. — Low tide at Waterford on St Mary's Bay, Nova Scotia. The exposed harbour floor makes tidal range visible.

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
Play the month and identify the two broad tidal bulges, one towards the Moon and one on the opposite side of Earth.
Open Observe
02
Tinker
Compare alignment of Sun and Moon with a right-angle arrangement. Describe the difference between spring and neap tides.
Open Tinker
03
Explain
Why is the tidal range larger when the Sun and Moon align than when they are at right angles?
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 the relative positions of the Moon and Sun produce the difference between spring and neap tides.

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.

Pause the animation at a useful moment. Ask students what should happen next, then play it to test their explanation.

Guide the demonstration

Play the month and identify the two broad tidal bulges, one towards the Moon and one on the opposite side of Earth.

Compare alignment of Sun and Moon with a right-angle arrangement. Describe the difference between spring and neap tides.

Discuss a common misconception

“Spring tides occur only during the spring season.” Spring tides are periods of relatively large tidal range around new and full Moon, when solar and lunar tide-generating effects reinforce each other. They occur throughout the year. The height and timing at an actual coast also depend on water depth, basin shape and local conditions.

Build the explanation

The Moon’s gravitational attraction varies across Earth, creating a tide-generating effect with two broad bulges. The Sun also contributes: aligned effects produce spring tides, while roughly perpendicular effects produce neap tides.

Compare alignment of Sun and Moon with a right-angle arrangement. Describe the difference between spring and neap tides.

These are equilibrium tides; coastlines, ocean depth and basin resonance strongly affect actual tidal heights and timing.

Teaching notes

Explain that spring tides refer to an increased tidal range and can occur in any season.

Include both sides of the equilibrium tidal pattern when discussing the Moon’s influence.

Distinguish astronomical tides from wind-driven storm surge and tsunami waves.

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.

Neap tide

First-quarter Moon photographed from Calabria, with the right half of the visible lunar disc sunlit. — The first-quarter Moon is near quadrature. Solar and lunar tidal effects then partly oppose, favouring neap tides; the local minimum tidal range can lag the quarter phase and depends on the coastline and basin.

Read the definition

Syzygy

The dark lunar disc surrounded by the Sun's pale corona during the 2017 total solar eclipse. — NASA's airborne view of the 21 August 2017 total solar eclipse. The Moon blocks the bright photosphere, revealing the corona.