# Tide

**tidalhigh tidelow tidespring tidetidesebb tidelow waterhigh waterneap tidetidal flow**

Several terms redirect here.wikipedia

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### Earth

**Earth's surfaceterrestrialworld**

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth.

The gravitational interaction between Earth and the Moon causes tides, stabilizes Earth's orientation on its axis, and gradually slows its rotation.

### Moon

**lunarthe MoonLuna**

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth.

Its gravitational influence produces the ocean tides, body tides, and the slight lengthening of the day.

### Tidal range

**MLTrangetidal coefficient**

Tide tables can be used for any given locale to find the predicted times and amplitude (or "tidal range"). Every 7 1⁄2 lunations (the full cycles from full moon to new to full), perigee coincides with either a new or full moon causing perigean spring tides with the largest tidal range.

Tidal range is the height difference between high tide and low tide.

### Slack water

**slack tidedodge tidedodge tides**

The moment that the tidal current ceases is called slack water or slack tide.

Slack water, also known as 'the stand of the tide', is a short period in a body of tidal water when the water is completely unstressed, and there is no movement either way in the tidal stream, and which occurs before the direction of the tidal stream reverses.

### Lunitidal interval

**High water interval**

Tides vary on timescales ranging from hours to years due to a number of factors, which determine the lunitidal interval.

The lunitidal interval measures the time lag from lunar culmination to the next high tide at a given location.

### Sea level

**mean sea levelMSLAMSL**

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth.

A common and relatively straightforward mean sea-level standard is instead the midpoint between a mean low and mean high tide at a particular location.

### Chart datum

**lowest astronomical tideMLLWmean lower low water**

These depths are relative to a "chart datum", which is typically the water level at the lowest possible astronomical tide (although other datums are commonly used, especially historically, and tides may be lower or higher for meteorological reasons) and are therefore the minimum possible water depth during the tidal cycle.

A chart datum is generally derived from some phase of the tide.

### Tidal force

**tidal forcestidaltidal effects**

Approximately twice a month, around new moon and full moon when the Sun, Moon, and Earth form a line (a configuration known as a syzygy ), the tidal force due to the Sun reinforces that due to the Moon.

The tidal force is a force that stretches a body towards and away from the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomena, including tides, tidal locking, breaking apart of celestial bodies and formation of ring systems within the Roche limit, and in extreme cases, spaghettification of objects.

### Earth tide

**earth tidesbody tidescrustal**

For example, the shape of the solid part of the Earth is affected slightly by Earth tide, though this is not as easily seen as the water tidal movements.

Though the gravitational forcing causing earth tides and ocean tides is the same, the responses are quite different.

### Perigean spring tide

**spring tidesking tideperigean**

Every 7 1⁄2 lunations (the full cycles from full moon to new to full), perigee coincides with either a new or full moon causing perigean spring tides with the largest tidal range.

A proxigean spring tide (also known as a perigean spring tide) is a tide that occurs three or four times per year when a perigee (the point nearest Earth that the Moon reaches during its 27.3-day elliptic orbit) coincides with a spring tide (when the Sun, the Moon, and Earth are nearly aligned every two weeks).

### Amphidromic point

**amphidromicAmphidromeamphidromes**

The predictions are influenced by many factors including the alignment of the Sun and Moon, the phase and amplitude of the tide (pattern of tides in the deep ocean), the amphidromic systems of the oceans, and the shape of the coastline and near-shore bathymetry (see Timing).

An amphidromic point, also called a tidal node, is a geographical location which has zero tidal amplitude for one harmonic constituent of the tide.

### Mean high water springs

**mean high water springMHWSMHW**

Mean high water springs (MHWS) is the highest level that spring tides reach on the average over a period of time (often 19 years).

### Tide gauge

**tide gaugestide measurermarigraph**

To make accurate records, tide gauges at fixed stations measure water level over time.

Tide gauges are used to measure tides and quantify the size of tsunamis.

### Tide clock

**certain clocks**

Simple tide clocks track this constituent.

Along many coastlines, the Moon contributes the major part (67%) of the combined lunar and solar tides.

### Seleucus of Seleucia

**Seleucus**

Seleucus of Seleucia theorized around 150 BC that tides were caused by the Moon.

Coming from Seleucia on the Tigris, Mesopotamia, the capital of the Seleucid Empire, he is best known as a proponent of heliocentrism and for his theory of the origin of tides.

### Isaac Newton

**NewtonSir Isaac NewtonNewtonian**

Isaac Newton (1642–1727) was the first person to explain tides as the product of the gravitational attraction of astronomical masses.

Newton used his mathematical description of gravity to prove Kepler's laws of planetary motion, account for tides, the trajectories of comets, the precession of the equinoxes and other phenomena, eradicating doubt about the Solar System's heliocentricity.

### New moon

**lunationnewlunar conjunction**

Approximately twice a month, around new moon and full moon when the Sun, Moon, and Earth form a line (a configuration known as a syzygy ), the tidal force due to the Sun reinforces that due to the Moon. Every 7 1⁄2 lunations (the full cycles from full moon to new to full), perigee coincides with either a new or full moon causing perigean spring tides with the largest tidal range.

Its precise duration is linked to many phenomena in nature, such as the variation between spring and neap tides (the most and least profound tidal variances respectively).

### Theory of tides

**Laplace's tidal equationstidal theorytidal analysis**

The Laplace tidal equations are still in use today.

The theory of tides is the application of continuum mechanics to interpret and predict the tidal deformations of planetary and satellite bodies and their atmospheres and oceans (especially Earth's oceans) under the gravitational loading of another astronomical body or bodies (especially the Moon and Sun).

### Dialogue Concerning the Two Chief World Systems

**DialogoDialogo sopra i due massimi sistemi del mondoDialogue**

Galileo Galilei in his 1632 Dialogue Concerning the Two Chief World Systems, whose working title was Dialogue on the Tides, gave an explanation of the tides.

He was ordered to remove all mention of tides from the title and to change the preface because granting approval to such a title would look like approval of his theory of the tides using the motion of the Earth as proof.

### Mean low water spring

**low tide levelMean Low Water MarkMLWS**

### Galileo Galilei

**GalileoGalileanGalilei**

Galileo Galilei in his 1632 Dialogue Concerning the Two Chief World Systems, whose working title was Dialogue on the Tides, gave an explanation of the tides.

Galileo considered his theory of the tides to provide such evidence.

### Gravity

**gravitationgravitationalgravitational force**

On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides.

### Tide table

**Tidal tabletide and current tablestide chart**

Tide tables can be used for any given locale to find the predicted times and amplitude (or "tidal range").

The dates of spring tides and neap tides, approximately seven days apart, can be determined by the heights of the tides on the classic tide tables: a small range indicates neaps and large indicates springs.

### Geoid

**geodetic sea levelundulation of the geoidgeoid height**

The ocean's surface is closely approximated by an equipotential surface, (ignoring ocean currents) commonly referred to as the geoid.

The geoid is the shape that the ocean surface would take under the influence of the gravity and rotation of Earth alone, if other influences such as winds and tides were absent.

### Diurnal cycle

**diurnalsemi-diurnaldiurnally**

Many shorelines experience semi-diurnal tides—two nearly equal high and low tides each day.

Often these can be related to lunar tides, in which case the interval is closer to 12 hours and 25 minutes.