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What are Tides and why do they occur?


Rise and fall of the oceans water level because of the gravitational forces of the sun and the moon are referred to as Tides. In other words, the gravitational pull of the moon and the rotational force of the earth cause tides to rise and fall. The waves generated by tides are called Tidal Waves.

The height of tides varies from place to place due to the depth of water, the coastal features and openness or closeness of the ocean or sea. As we know that the sun is far bigger than the moon but the gravitational force of the moon is double than of the sun, it is so because the sun is at a greater distance than the moon from the earth. Every place, along the coast, experiences tides and ebbs twice in 24 hours.

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As we know that when the sun, the earth and the moon are aligned in a straight line this position is called as SYZYGY. All these celestial bodies are responsible for the tides. There are basically two types of tides namely; spring tide and neap tide.

The combined forces of the sun and the moon resulted into High Tides or Spring Tides. High tides are experienced on the full moon and the new moon. Unlike this, when the sun, the earth and the moon are aligned in a right angle position, the gravitational forces of the sun and the moon work against each other, when Neap or Low Tides are experienced. The position occurs on the seventh or eighth day of each fortnight. Neap tides are generally 20% lower than the normal tides whereas spring tides are 20% higher than the normal tides.

The part of the earth facing the moon experiences a tide due to the gravitational pull of the moon, but at the same time, the part of the earth on the opposite side also experiences a tide. This is due to the strong centrifugal force to balance the rotation of the earth.

Along the coast, such place should experience tides at an interval of 12 hours, but it’s not so. The second tide is experienced after a lag of 26 minutes. This is often because the relative motions of the moon with respect to the earth.


  • Equilibrium or Gravitational theory of Sir Isaac Newton in 1687
  • Dynamical theory of Laplace in 1755
  • Progressive Wave Theory of William Whewell in 1833
  • Canal Theory of AG Airy in 1842
  • Stationary Wave Theory of AR Harris


When the moon comes in between the sun and the earth, is called a solar eclipse. On the other hand, when the earth comes between the sun and the moon is called a lunar eclipse. On a full moon, the lunar eclipse always occurs and a solar eclipse occurs on the new moon. There would be a maximum seven occasions for the lunar and solar eclipses in one year it so as because lunar and solar eclipses do not take place on every full moon and new moon respectively.

It happens due to the inclination of the moon to 5 degree on its own axis. Moreover, when the earth and the moon reach the same point of the revolutionary path, the moon moves a little bit ahead of the earth as a result, eclipse does not occur on every new and full moon.

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