Although the distance between the Earth and the Moon are the most significant factor for the tides, the position of the three stars also is of consideration. In Full Moon, when the Moon is in opposition (the Moon in a side or end, the Earth in the center and the Sun in the other), the force of attraction of both is added and the tides are higher. These tides are called alive tides or of sicigia.

The same happens in New Moon, when the Moon is between the Earth and the Sun. Greater attraction is on the Earth side, but also smaller force will be on the other side, producing a high tide also here by the centrifugal Earth force. On the contrary, when the Moon is in quadrature (first quarter or third quarter), the force of gravitational attraction of the Sun and the Moon is contrary and the tides are small. These tides are called dead tides.

The influences are added twice each year. The distance and the position of the Moon and the Sun, with respect to the Earth, agree to favor the alive tides more discharges of the year in the equinoxes. Then the equinoctial tides of sicigias occur.

The variations in the level of the sea, the tides, are associated with several phenomena; and the commonest predictable one is the astronomical one, product of the force caused by the gravitational attraction of the Moon, and in smaller degree, of the Sun. These phenomena are predictable with enough exactitude since they depend on the position of the stars, which can indeed be well known. For example, we can calculate to the hour and height of the high tide for a day within 2000 years.

The tides in the great water bodies are more evident: the oceans, seas and lakes. But also tides in the solid part of the Earth take place.