Sun, Moon and Earth: the tidal variables

Tides are the sum of the effects caused by the gravitational attraction of the Moon and the Sun, as well as the gravitational force of the Earth.

The Moon's gravitational force is only 17% of the Earth's gravity. The Sun's impact over the Earth is 46% of that caused by the Moon. This means that the Moon tries to pull everything from the Earth, our planet holds everything, except water.

When the Moon is in line with one side of the Earth, it pulls the water causing the high tide. Because the Earth rotates on its axis the moon completes one orbit in our sky every 25 hours, we get two tidal peaks as well as two tidal troughs, every 12 hours.

Since the Moon moves around the Earth, it is not always in the same place at the same time each day. So, each day, the times for high and low tides change by 50 minutes.

When the Moon, Earth and Sun are perfectly aligned, the sum of the gravitational pull of the Sun and Moon cause maximum tide or extreme tides. When the Moon lies between Earth and the Sun we get the New Moon.

When the Moon is on the opposite side of the Earth from the Sun we get the Full Moon. In these cases both tides are 20% higher and lower than the usual tides.

The Guinness Book of World Records declared that Burntcoat Head, Nova Scotia has the highest tides in the world. The Bay of Fundy holds a measurement of a 17-meter (55.8 feet) tidal range.

In many surf spots, surfing is only possible in low and high tides, when combined with a determined swell and wind. In other wave peaks, middle tide conditions may be the best moment to hit the surf.

All these variables can be combined with the ocean floor and the shore geography to establish standard patterns for above the average surfing days.

Discover the tidal "Rule of Twelfths" in surfing.