What Causes Tides?

The Invisible Pull

If you spend a long, beautifully relaxing day sitting at the beach, you will slowly notice something incredibly bizarre: the ocean completely refuses to stay put. Over the course of several hours, the entire massive body of water will creep high up the wet sand (High Tide) and then slowly retreat hundreds of feet back out to sea (Low Tide).

The water isn't magically disappearing into a hole in the seafloor, and it isn't rapidly evaporating into the sky. The water is literally being dragged violently across the face of the Earth by an unimaginably massive, entirely invisible force of gravity.

While the solid, rocky Earth is massive, the incredibly heavy Moon floating quietly 238,000 miles away in the dark vacuum of space possesses its own gravitational pull.

A breathtaking cinematic photograph of a massive, dramatic high tide ocean wave crashing against dark rocks under a glowing full moon

The Oceanic Bulge

As the Moon orbits gracefully around the Earth, its intense, invisible gravity acts like a massive magnetic tractor beam pulling aggressively on the Earth's liquid oceans. The water directly facing the Moon literally bulges outward toward it, piling up high against the nearest shore. This massive, planetary water bulge immediately creates what you experience as a high tide.

Interestingly, there is actually a second, massive high tide simultaneously occurring on the exact opposite side of the Earth at the exact same time! This bizarre phenomenon happens because the Moon's gravity effectively pulls the entire solid center of the Earth slightly away from the loose water sitting on the far side, leaving a second massive bulge completely behind.

A cinematic documentary-style illustration of the Earth from space showing the Moon pulling the ocean into massive bulges

Because the Earth spins beautifully like a top on its axis once every 24 hours, your specific sandy beach is simply slowly rotating through the water. It routinely rotates into a deep bulge (experiencing a massive High Tide) and then smoothly rotates out of the shallow bulge (experiencing a dry Low Tide) exactly twice a day.

The Sun's Tug-Of-War

Furthermore, the incredibly massive Sun also exerts a huge gravitational pull on the fragile oceans! Even though the Sun is 93 million miles away, its immense gravity still reaches us.

When the massive Sun, Earth, and Moon perfectly align in a straight row (like during a full moon or a new moon), they pull the water together as an incredibly powerful team. This intense, combined gravitational force successfully creates massive, extreme high tides affectionately known as Spring Tides.

Conversely, when the Sun and Moon are entirely out of alignment and pulling on the Earth at a harsh 90-degree angle, they are playing a cosmic game of tug-of-war. They fight each other's gravity, canceling out the pull and resulting in incredibly weak, boring tides known as Neap Tides.