SPRING vs. NEAP TIDES

TIDES

The lunar dayTidal bulges follow the Moon as it rotates around EarthLunar day is 50 minutes longer than a solar day because the Moon is moving in its orbit around Earth

The Earth’s rotation pushes the tide ahead of the moon

High Tide Pushed Ahead of Moon

The interaction between the Earth’s rotation pushing the tides ahead of the moon and tidal forces squeezing the tides toward the moon is slowly slowing down the rotation of Earth.

Relative sizes and distances of the Earth, Moon, and SunThe Sun is much more massive than the Moon but much further away

Solar bulges are 46% the size of lunar bulges

Effect of elliptical orbits

Tidal ranges are greater when:• The Moon is at perigee (point closest to the Earth)

• The Earth is at perihelion (point closest to the sun)

The sun also affects tides. The combined forces of the sun and the moon on Earth result in tidal ranges that vary based on the positions of the three bodies.

A tidal range is the difference between levels of ocean water at high tide and low tide.

The monthly tidal cycle (29.5 days)About every 7 days, Earth alternates between:Spring tide

• Alignment of Earth-Moon-Sun system in straight line.

• LUNAR PHASE• New Moon or Full Moon

• Lunar and solar bulges constructively interfere

• Large tidal range

Neap tide• Earth-Moon-Sun system at right angles

• LUNAR PHASE• 1st Quarter or 3rd Quarter

• Lunar and solar bulges destructively interfere

• Small tidal range

Different types of tide

Sun

Earth

Moon

Spring tides occur when the sun and moon are in a straight line

The tidal range is typically highest during spring tides…meaning locations will have a higher high tide and a lower low tide.10

Different types of tide

Neap tides occur when the sun and moon form a right angle with Earth

Smaller difference between high and low tides.

Low tides are typically higher than normal and high tides are lower than normal

Earth

Moon

Sun

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