“The Earth experiences two high tides and two low tides each day.”

Many people observe the rhythmic rise and fall of ocean waters and correctly note that the coast experiences two high tides and two low tides within a cycle. However, the precise timing of this daily occurrence is where a common misconception often arises. While it might seem like these tidal events align perfectly with a 24-hour solar day, the actual period is slightly longer, leading to a subtle but significant difference over time.

The true cause of these regular tidal fluctuations is primarily the gravitational pull of the moon, with a lesser influence from the sun. As the moon orbits Earth, its gravity creates a bulge of water on the side of our planet closest to it. Interestingly, an equally significant bulge forms on the opposite side of Earth. This happens because the moon pulls the Earth itself away from the water on the far side, leaving that water to bulge outwards. As Earth rotates, coastal areas pass through these two bulges, experiencing two high tides, and through the areas of lower water level in between, resulting in two low tides.

The reason these events don't perfectly match a 24-hour day is due to the moon's own orbit. By the time Earth completes a 24-hour rotation, the moon has moved slightly in its orbit. For a specific point on Earth to be directly beneath the moon again, it takes an additional 50 minutes. This means that a full tidal cycle, from one high tide to the next corresponding high tide, actually takes approximately 24 hours and 50 minutes, a period known as a lunar day. People commonly believe the cycle aligns with a standard 24-hour day because the difference of 50 minutes is not immediately obvious in casual observation and the general pattern of twice-daily tides holds true.