Does the moon really cause high tide

Ebb and flow: this is how the tides are created

Status: 02.01.2020 10:18 a.m.
The difference between ebb and flow is particularly evident in the Wadden Sea.

The oceans are constantly in motion: The attraction of the moon sets the water masses of the oceans in motion and causes ebb, i.e. running water, and high tide on the coasts, at which the water rises again. On the open sea, the tidal range - i.e. the difference between high and low tide - is only about 30 centimeters, on the coasts it sometimes causes high fluctuations. In the rhythm of the tides, one of the most biodiverse natural landscapes in the world was created on the North Sea, stretching from Den Helder in the Netherlands to Esbjerg in Denmark - the Wadden Sea. But there are also places elsewhere in the world where the seabed regularly dries up.

The moon's gravity causes ebb and flow

The tides are created by the interaction of the earth and the moon. Although the moon is several hundred thousand kilometers from the earth, it attracts the water of our planet through the action of its gravitational forces. These forces depend on the distance and create flood mountains and ebb valleys. On the side of the earth facing the moon, the gravitational force is greater than the centrifugal force and the water is drawn towards the moon - a flood mountain is created. On the side facing away from the moon, the gravitational force of the moon is smaller than the centrifugal force. The water masses shift in the opposite direction and a second flood mountain arises. Put simply, the earth rotates under the flood mountains during its daily rotation. As a result, there is high tide twice a day and low tide twice a day.

Earth's crust rises and falls

Because the earth rotates once on its axis within exactly one day, but the moon moves a little further at the same time, the earth needs an average of 24 hours and 50 minutes to catch up with the moon. Therefore it takes about 12 hours and 25 minutes from high tide to high tide and 12 hours and 25 minutes from low tide to low tide. Incidentally, the moon not only sets the water masses on earth in motion - the earth's crust also rises and falls a little.

Spring and sipping tides

The height of the rising water on the coasts is different every day and depends on the position of the moon in relation to the earth and the sun, whose force of attraction also acts on the earth. With a full moon and a new moon, the sun, moon and earth stand in a row, then the effects are intensified. The high tide is higher, the low tide lower: A "spring tide" occurs. In the case of a half moon, when the sun, moon and earth are at right angles to one another, the effects weaken. The high tide is less high, the low tide is particularly low, there is a "nipp tide".

The tides as a source of energy

The energy of the water currents that arise in the course of the tides is immense and - just like that of the sun and wind - regenerative, i.e. inexhaustible. Researchers estimate that waves and tides could cover five to ten percent of the world's electricity needs. So far, however, the sea has hardly been used as a source of energy. Research is therefore carried out on so-called tidal power plants.

The Orkney Islands are exploring the use of marine power

On the British Orkney Islands, the European Marine Energy Center (EMEC for short) enables energy companies to research and develop wave and tidal power plants. The tides are particularly strong on the islands and cause waves up to 19 meters high. In a tidal power plant, rotors make use of the energy generated by water movements and generate electricity that is transported to the mainland via an underwater cable and fed into the power grid. The first tidal power plant was built in Brittany in the 1960s.

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Arte | Xenius | 01/01/2019 | 06:05 am