A fishing boat rests on exposed mud beside a wharf at low tide in Nova Scotia.

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Preparing the 3D view

Preparing lighting and the first complete frame…

Model scale

Earth–Moon sizes enlarged. blue surface is exaggerated tidal potential.

Day 11.8 of an ideal synodic month · 90.3% illuminated · Moon 384.4 thousand km away.

How to read these results

Lunar tidal strength ∝ 1/r³; solar contribution 0.46 at mean lunar distance. Earth rotates while the potential follows the Moon–Sun geometry. No tide times, flood heights or coast-specific forecast.

Tides

Explain how the relative positions of the Moon and Sun produce the difference between spring and neap tides.

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Why it happens

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.

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Low tide at Waterford on St Mary's Bay, Nova Scotia. The exposed harbour floor makes tidal range visible.

Try a comparison

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

Reading the result

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

A common misunderstanding

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.

Cases

Exam language

Spring tide

A tide with a relatively large range, occurring around new and full Moon when solar and lunar tide-generating effects reinforce each other. Spring refers to the larger tidal range, rather than the season. Local coastlines and basins modify the response.

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Low water at St Mary's Bay, Nova Scotia. Tidal range changes through the spring–neap cycle as lunar and solar tidal effects combine. This single low-tide photograph does not establish whether it was a spring or neap tide.

Neap tide

A period of relatively small tidal range, usually near the first and third quarters of the Moon. The Sun’s and Moon’s tide-generating effects partly oppose one another. Local coastal geometry and tidal timing modify the range observed.

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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.

Syzygy

An approximately straight-line alignment of three celestial bodies. In the Sun–Earth–Moon system it occurs around new and full Moon and contributes to spring tides. An eclipse also requires sufficiently close alignment with the relevant orbital node and shadow.

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NASA's airborne view of the 21 August 2017 total solar eclipse. The Moon blocks the bright photosphere, revealing the corona.

Quadrature

The arrangement in which the Sun and Moon appear about 90 degrees apart from Earth, near a quarter Moon. This geometry is associated with neap tides, although local tides respond with delays and are shaped by their ocean basin.

Tidal bulge

An idealised elevation of the ocean surface in an equilibrium-tide model. Real tides are moving waves modified by basin shape, depth, rotation and coastlines.

Tidal range

The vertical difference between a high tide and the neighbouring low tide at a location. It generally increases around spring tides and decreases around neap tides. Coastal shape, water depth and basin resonance strongly influence the local range.

Semi-diurnal tide

A tidal pattern with two high waters and two low waters in each lunar day, which averages about 24 hours 50 minutes.

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