The Moon & Tides

How the Moon Creates Tides

Tides are caused by the differential gravitational pull of the Moon on different parts of Earth. The side of Earth facing the Moon experiences a stronger gravitational pull than the center of Earth, and the center experiences a stronger pull than the far side.

This differential creates two tidal bulges:

• Near-side bulge: Water on the side of Earth closest to the Moon is pulled toward the Moon more strongly than the solid Earth beneath it, creating a bulge of water.
• Far-side bulge: On the opposite side of Earth, the solid Earth is pulled toward the Moon more than the water (which is farther away), effectively leaving a second bulge of water behind.

As Earth rotates beneath these two bulges, most coastlines experience two high tides and two low tides roughly every 24 hours and 50 minutes — the 50-minute offset matching the Moon's daily delay in rising and setting.

Spring Tides and Neap Tides

The Sun's Role

While the Moon is the primary driver of tides, the Sun also contributes — about 46% as much as the Moon despite being much farther away (its enormous mass compensates for the distance).

When the Sun and Moon work together (spring tides), the tidal range can be 40% larger than when they work against each other (neap tides). This is why the highest tides of the year often occur near equinoxes during New Moon or Full Moon, when the Sun is directly over the equator.

Moonrise, Moonset, and Tidal Timing

There's a direct connection between when the Moon rises/sets and when tides occur:

• High tide generally occurs when the Moon is near its highest point in the sky (transit) and again about 12 hours and 25 minutes later when the Moon is on the opposite side of Earth.
• Low tide falls roughly halfway between high tides — when the Moon is near the horizon (rising or setting).
• The actual timing varies by location due to the shape of coastlines, ocean basins, and underwater topography.

Knowing your moonset time gives you a rough indicator of when to expect lower tides at your location. Use our calculator for precise times.

Extreme Tides: The Bay of Fundy

The Bay of Fundy in eastern Canada experiences the most extreme tides on Earth — with tidal ranges up to 53 feet (16 meters). This is about 10 times the global average tidal range.

The extreme tides are caused by:

• The bay's funnel shape, which amplifies the incoming tidal wave
• Resonance — the bay's length closely matches the natural period of oscillation for the Atlantic tidal wave
• The enormous volume of water (100 billion tonnes) that flows in and out with each tide cycle

Tidal Effects Beyond the Ocean

The Moon's tidal forces don't just affect water:

• Earth tides: The solid Earth itself rises and falls by about 30 cm (12 inches) twice daily due to the Moon's pull.
• Atmospheric tides: The atmosphere also experiences tidal effects, though these are overwhelmed by weather patterns.
• Tidal heating: On Jupiter's moon Io, tidal forces from Jupiter generate enough internal heat to make Io the most volcanically active body in the solar system.
• Tidal locking: Over billions of years, Earth's tides have slowed the Moon's rotation until it became tidally locked — always showing the same face to Earth.