High Water and Low Water|
Regularly two times a day, the water of the oceans rises and falls. These phenomena are called low respectively high water. It takes the water 6 hours both to rise and to fall again; in between it rests for nearly one hour (high respectively low tide). The interaction of rising and falling water is called tide.
The dynamics of the tides lies in the interaction of two different forces, which have an effect on the water-cover which encloses the globe:
It takes the Moon 28 days to revolve around the Earth, which rotates around its axis once a day. Due to the Moon's direction of rotation, it takes more than 24 hours until the original point, i.e. in this case the tidal wave, faces the Moon again. The time delay is 50 minutes. Therefore, high and low tide are postponed for 25 minutes a day. |
One tide is the period of time between two phases of high and low tide and lasts 12 h and 25 min..
During their annual course, the Sun, the Earth and the Moon occupy different positions to each other. Thereby, the forces of attraction, taking an effect on the water-cover of the Earth, change: At times of New and Full Moon, these celestial bodies occupy positions on one axis, which means the forces of gravity add and the tidal waves increase. This phenomenom is called spring tide, which is characterized by more extreme high and low water. If they occupy positions in a right angle to each other, the forces gravity of the Sun and the Moon partly extinguish each other. Thereby, neap tides are caused, which are characterized by more moderate high and low water.