Simplified schematic of only the lunar portion of Earth's tides, showing (exaggerated) high tides at the sublunar point and its antipode for the hypothetical case of an ocean of constant depth without land. Solar tides not shown.
In Maine (U.S.), low tide occurs roughly at moonrise and high tide with a high Moon, corresponding to the simple gravity model of two tidal bulges; at most places however, the Moon and tides have a phase shift.
Types of tides (See Timing (below) for coastal map)
Illustration by the course of half a month
The types of tides
Low tide at Bangchuidao scenic area, Dalian, Liaoning Province, China
Low tide at Ocean Beach in San Francisco, California, U.S.
Low tide at Bar Harbor, Maine, U.S. (2014)
M2 tidal constituent. Red is most extreme (highest highs, lowest lows), with blues being least extreme. White cotidal lines converge in blue areas indicating little or no tide.  The curved arcs around these convergent areas are amphidromic points.  They show the direction of the tides, each indicating a synchronized 6-hour period. Tidal ranges generally increase with increasing distance from amphidromic points. Tide waves move around these points, generally counterclockwise in the N. Hemisphere and clockwise in the S. Hemisphere
Brouscon's Almanach of 1546: Compass bearings of high waters in the Bay of Biscay (left) and the coast from Brittany to Dover (right).
Brouscon's Almanach of 1546: Tidal diagrams "according to the age of the moon".
The lunar gravity differential field at the Earth's surface is known as the tide-generating force. This is the primary mechanism that drives tidal action and explains two equipotential tidal bulges, accounting for two daily high waters.
The harbour of Gorey, Jersey falls dry at low tide.
The same tidal forcing has different results depending on many factors, including coast orientation, continental shelf margin, water body dimensions.
A regular water level chart
Tidal prediction summing constituent parts. The tidal coefficients are defined on the page theory of tides.
Tides at Bridgeport, Connecticut, U.S. during a 50-hour period.
Tides at Bridgeport, Connecticut, U.S. during a 30-day period.
Tides at Bridgeport, Connecticut, U.S. during a 400-day period.
Tidal patterns in Cook Strait. The south part (Nelson) has two spring tides per month, versus only one on the north side (Wellington and Napier).
US civil and maritime uses of tidal data
Tidal Indicator, Delaware River, Delaware c. 1897. At the time shown in the figure, the tide is 1 1⁄4 feet above mean low water and is still falling, as indicated by pointing of the arrow. Indicator is powered by system of pulleys, cables and a float. (Report Of The Superintendent Of The Coast & Geodetic Survey Showing The Progress Of The Work During The Fiscal Year Ending With June 1897 (p. 483))
A rock, seen at low water, exhibiting typical intertidal zonation.
Spring tide: Sun and Moon on the same side (0°)
Neap tide: Sun and Moon at 90°
Spring tide: Sun and Moon at opposite sides (180°)
Neap tide: Sun and Moon at 270°
Spring tide: Sun and Moon at the same side (cycle restarts)

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.

- Tide

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Earth's only natural satellite.

The near side of the Moon (north is at top)
The Moon and selected moons of the Solar System, with Earth to scale. Nineteen moons are large enough to be round, several having subsurface oceans and one, Titan, having a considerable atmosphere.
Sketch by the Apollo 17 astronauts. The lunar atmosphere was later studied by LADEE.
Map of the near side of the Moon and its features, with major maria (blue) and craters (brown) marked.
Topography of the Moon
The largest mare, the main dark region of the near side, is Oceanus Procellarum, with smaller mare, such as Imbrium and Serenitatis, that sit within its ring. Left of the centerline is Procellarum proper.
Lunar crater Daedalus on the Moon's far side
Lunar Reconnaissance Orbiter Wide Angle Camera image of the lunar swirl Reiner Gamma
Relative elemental composition of the lunar soil
Earth–Moon system (schematic)
DSCOVR satellite sees the Moon passing in front of Earth
Comparison between the Moon on the left, rotating tidally locked (correct), and with the Moon on the right, without rotation (incorrect).
Libration, the slight variation in the Moon's apparent size and viewing angle over a single lunar month as viewed from Earth's north.
During the lunar phases, only portions of the Moon can be observed from Earth.
Appearence of the Moon when visible at daytime
The Moon, tinted reddish, during a lunar eclipse
Galileo's sketches of the Moon from the ground-breaking Sidereus Nuncius, publishing among other findings the first descriptions of the Moons topography.
Map of the Moon by Johannes Hevelius from his Selenographia (1647), the first map to include the libration zones
First view in history of the far side of the Moon, taken by Luna 3, 7 October 1959
The first image from the lunar surface, photographed by Luna 9 in 1966.
A replica of Lunokhod 1, which reached the Moon becoming the first remote controled rover on an extraterrestrial surface (1970)
Earthrise, the first colour image of Earth taken by a human from the Moon, during Apollo 8 (1968) the first time a crewed spacecraft left Earth orbit and reached another astronomical body.
Neil Armstrong, the first human on the Moon, working at the Lunar Module Eagle, a first lunar base, during Apollo 11 (1969), the first Moon landing
One of the first moon rocks (Lunar basalt 70017, Apollo 17, 1972), which were collected during the Apollo missions.
NASA's Moon Mineralogy Mapper equipment on India's Chandrayaan-1 for the first time discovered in 2008 water-rich minerals (light blue), shown in blue around a small crater from which it was ejected.
Map of all soft landing sites on the near side of the Moon.
Remains of human activity, Apollo 17's Lunar Surface Experiments Package.
A photo of the reflector of the Lunar Laser Ranging Experiment of Apollo 11, still in use.
The Venus of Laussel (c. 25,000 BP) holding a crescent shaped horn, the 13 notches on the horn may symbolize the number of days from menstruation to ovulation, or of menstrual cycles or moons per year.
Scale model of the Earth–Moon system: Sizes and distances are to scale.
The geologic map of the Moon at 1-2.5M scale by Chinese Academy of Sciences. See the original file for higher resolution.
Comparison of angular diameter of the Moon compared to other celestial objects (to get a true representation of this image view it at a size of 5 cm wide on your monitor and at 5.15 m distance).

Orbiting Earth at an average distance of 384400 km, or about 30 times Earth's diameter, its gravitational influence very slowly lengthens Earth's day and is the main driver of Earth's tides.

Storm surge

Coastal flood or tsunami-like phenomenon of rising water commonly associated with low-pressure weather systems, such as cyclones.

Hurricane Ike storm surge damage in Gilchrist, Texas in 2008.
Example of a SLOSH run
Elements of a storm tide at high tide
Total destruction of the Bolivar Peninsula (Texas) by Hurricane Ike's storm surge in September 2008

Other factors affecting storm surge severity include the shallowness and orientation of the water body in the storm path, the timing of tides, and the atmospheric pressure drop due to the storm.

Intertidal zone

Tide pools at Pillar Point showing zonation on the edge of the rock ledge
A rock, seen at low tide, exhibiting typical intertidal zonation, Kalaloch, Washington, western United States.
A California tide pool in the low tide zone
Nutrition Pollution in Assateague Island National Seashore, Maryland
Mussels in the intertidal zone in Cornwall, England.
Barnacles and limpets in the intertidal zone near Newquay, Cornwall, England.
A tidal pool in the intertidal zone during low tide, Sunrise-on-Sea, South Africa.
Unexplained crumbs of sand that appear to have been deposited around stone by escaping air.
Rocks in intertidal zone completely covered by mussels, at Bangchuidao Scenic Area, Dalian, Liaoning Province, China.

The intertidal zone, also known as the foreshore or seashore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range).


Third planet from the Sun and the only astronomical object known to harbor life.

A photograph of Earth taken by the crew of Apollo 17 in 1972. A processed version became widely known as The Blue Marble.
Planetary disk of a star, the inner ring has a radius equal to Earth and the Sun
Artist's impression of earth during the Archean eon, showing falling meteor, erupting volcano, round stromatolites, and barren landscape
Earth topological map, the area is redder if it is raised higher in real-life
Global map of heat flow from Earth's interior to the surface
Earth's major plates, which are: · ·  ·  ·  ·
Satellite picture of Upsala Glacier, showing mountains, icebergs, lakes, and clouds
Schematic of Earth's magnetosphere, with the solar wind flows from left to right
Earth's rotation imaged by Deep Space Climate Observatory, showing axis tilt
Illustration of the Earth, Earth's orbit, the Sun and the four seasons
Earth's axial tilt and its relation to the rotation axis and planes of orbit
Earth-Moon system seen from Mars
A model of Vanguard 1, the oldest human-made object in Earth orbit
Water is transported to various parts of the hydrosphere via the water cycle
Top of Earth's blue-tinted atmosphere, with the Moon at the background
Fungi are one of the kingdoms of life on Earth.
The seven continents of Earth:
Earth's land use for human agriculture
Change in average surface air temperature since the industrial revolution, plus drivers for that change. Human activity has caused increased temperatures, with natural forces adding some variability.
Earthrise, taken in 1968 by William Anders, an astronaut on board Apollo 8

The Moon always faces the Earth with the same side through tidal locking and causes tides, stabilizes Earth's axis, and gradually slows its rotation.

Tidal force

Figure 4: The Moon's gravity differential field at the surface of the Earth is known (along with another and weaker differential effect due to the Sun) as the Tide Generating Force. This is the primary mechanism driving tidal action, explaining two tidal equipotential bulges, and accounting for two high tides per day. In this figure, the Earth is the central blue circle while the Moon is far off to the right. The outward direction of the arrows on the right and left indicates that where the Moon is overhead (or at the nadir) its perturbing force opposes that between the earth and ocean.
Figure 3: Graph showing how gravitational attraction drops off with increasing distance from a body
Figure 5: Saturn's rings are inside the orbits of its principal moons. Tidal forces oppose gravitational coalescence of the material in the rings to form moons.
Figure 1: Comet Shoemaker-Levy 9 in 1994 after breaking up under the influence of Jupiter's tidal forces during a previous pass in 1992.
Figure 6: Tidal force is responsible for the merge of galactic pair MRK 1034.
Figure 7: Graphic of tidal forces. The top picture shows the gravity field of a body to the right, the lower shows their residual once the field at the centre of the sphere is subtracted; this is the tidal force. See Figure 4 for a more detailed version

The tidal force is a gravitational effect that stretches a body along the line towards 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.

Tide gauge

Device for measuring the change in sea level relative to a vertical datum.

A tide gauge
The tide gauge in Kronstadt, Russia
Interior view of Cascais Tide Gauge showing data recording equipment

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

Chart datum

Water level surface serving as origin of depths displayed on a nautical chart.

U.S. civil and maritime uses of tidal data

A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum.

Diurnal cycle

Any pattern that recurs every 24 hours as a result of one full rotation of the planet Earth around its axis.

Earth's rotation relative to the Sun causes the 24-hour day/night cycle.
Diurnal variation of air temperature (blue) lag by 3 to 4 hours behind insolation at solar noon (red).

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

Tide table

Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and levels of high and low tides, usually for a particular location.

A tide table for Monterey Bay Aquarium

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.

Isaac Newton

English mathematician, physicist, astronomer, alchemist, theologian, and author (described in his time as a "natural philosopher") widely recognised as one of the greatest mathematicians and physicists of all time and among the most influential scientists.

Portrait of Newton at 46 by Godfrey Kneller, 1689
Sir Isaac Newton
Newton in 1702 by Godfrey Kneller
Replica of Newton's second reflecting telescope, which he presented to the Royal Society in 1672
Illustration of a dispersive prism separating white light into the colours of the spectrum, as discovered by Newton
Facsimile of a 1682 letter from Isaac Newton to Dr William Briggs, commenting on Briggs' A New Theory of Vision.
Engraving of a Portrait of Newton by John Vanderbank
Newton's own copy of his Principia, with hand-written corrections for the second edition, in the Wren Library at Trinity College, Cambridge.
Isaac Newton in old age in 1712, portrait by Sir James Thornhill
Coat of arms of the Newton family of Great Gonerby, Lincolnshire, afterwards used by Sir Isaac.
Newton's tomb monument in Westminster Abbey
A Wood engraving of Newton's famous steps under the apple tree.
Newton statue on display at the Oxford University Museum of Natural History
Newton (1795, detail) by William Blake. Newton is depicted critically as a "divine geometer".

Newton used his mathematical description of gravity to derive 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.