Changes

==Etymology==

==Etymology==

[https://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English], time, from [https://nordan.daynal.org/wiki/index.php?title=English#ca._600-1100.09THE_OLD_ENGLISH.2C_OR_ANGLO-SAXON_PERIOD Old English] tīd; akin to Old High German zīt time and perhaps to [[Greek]] daiesthai  to divide

[https://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English], time, from [https://nordan.daynal.org/wiki/index.php?title=English#ca._600-1100.09THE_OLD_ENGLISH.2C_OR_ANGLO-SAXON_PERIOD Old English] tīd; akin to Old High German zīt time and perhaps to [[Greek]] daiesthai  to divide

*Date: before [http://www.wikipedia.org/wiki/11th_Century 12th century]

*Date: before [https://www.wikipedia.org/wiki/11th_Century 12th century]

==Definitions==

==Definitions==

*1 a obsolete : a [[space]] of [[time]] : period  

*1 a obsolete : a [[space]] of [[time]] : period  

:c : the overflow of a flooding stream

:c : the overflow of a flooding stream

==Description==

==Description==

'''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 tides occur with a period of approximately 12.5 hours and with an [[amplitude]] that is [[influenced]] by the alignment of the sun and moon and the shape of the [http://en.wikipedia.org/wiki/Bathymetry near-shore bottom].

'''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 tides occur with a period of approximately 12.5 hours and with an [[amplitude]] that is [[influenced]] by the alignment of the sun and moon and the shape of the [https://en.wikipedia.org/wiki/Bathymetry near-shore bottom].

Most coastal areas [[experience]] two daily high (and two low) tides. One of these high tides is at the point on the [[earth]] which is closest to the [[moon]]. The other high tide is at the [[opposite]] point on the [[earth]]. This is because at the point right "under" the [[Moon]] (the sub-lunar point), the water is at its closest to the Moon, so it [[experiences]] stronger [[gravity]] and is raised. On the opposite side of the Earth (the antipodal point), the water is at its farthest from the moon, so it is pulled less; at this point the Earth moves more toward the Moon than the water does—causing that water to "rise" ([[relative]] to the [[Earth]]) as well. In between the sub-lunar and antipodal points, the [[force]] on the water is diagonal or transverse to the sub-lunar/antipodal [[axis]] (and always towards that axis), resulting in low tide.

Most coastal areas [[experience]] two daily high (and two low) tides. One of these high tides is at the point on the [[earth]] which is closest to the [[moon]]. The other high tide is at the [[opposite]] point on the [[earth]]. This is because at the point right "under" the [[Moon]] (the sub-lunar point), the water is at its closest to the Moon, so it [[experiences]] stronger [[gravity]] and is raised. On the opposite side of the Earth (the antipodal point), the water is at its farthest from the moon, so it is pulled less; at this point the Earth moves more toward the Moon than the water does—causing that water to "rise" ([[relative]] to the [[Earth]]) as well. In between the sub-lunar and antipodal points, the [[force]] on the water is diagonal or transverse to the sub-lunar/antipodal [[axis]] (and always towards that axis), resulting in low tide.

The [[sun]] also exerts a (less powerful) [[gravitational]] [[attraction]] on the [[earth]] which results in a secondary tidal effect. When the earth, [[moon]] and [[sun]] are approximately aligned these two tidal effects reinforce one another (resulting in higher highs and lower lows). This alignment occurs approximately twice a month (around the [http://en.wikipedia.org/wiki/Full_moon full] and [http://en.wikipedia.org/wiki/New_moon new moon]). These recurring, extreme tides are termed [http://en.wikipedia.org/wiki/Spring_tide spring tides]. The opposite, most moderate tides are termed [http://en.wikipedia.org/wiki/Neap_tide neap tides].

The [[sun]] also exerts a (less powerful) [[gravitational]] [[attraction]] on the [[earth]] which results in a secondary tidal effect. When the earth, [[moon]] and [[sun]] are approximately aligned these two tidal effects reinforce one another (resulting in higher highs and lower lows). This alignment occurs approximately twice a month (around the [https://en.wikipedia.org/wiki/Full_moon full] and [https://en.wikipedia.org/wiki/New_moon new moon]). These recurring, extreme tides are termed [https://en.wikipedia.org/wiki/Spring_tide spring tides]. The opposite, most moderate tides are termed [https://en.wikipedia.org/wiki/Neap_tide neap tides].

Tide [[prediction]] is important for coastal [[navigation]]. The [http://en.wikipedia.org/wiki/Intertidal_zone intertidal zone], the strip of seashore that high tide submerges and low tide exposes, is an important [http://en.wikipedia.org/wiki/Tide#Intertidal_ecology ecological product] of ocean tides.

Tide [[prediction]] is important for coastal [[navigation]]. The [https://en.wikipedia.org/wiki/Intertidal_zone intertidal zone], the strip of seashore that high tide submerges and low tide exposes, is an important [https://en.wikipedia.org/wiki/Tide#Intertidal_ecology ecological product] of ocean tides.

While tides are usually the largest [[source]] of short-term sea-level fluctuations, sea levels are also subject to [[forces]] such as wind and barometric pressure changes, resulting in [http://en.wikipedia.org/wiki/Storm_surge storm surges], especially in shallow seas and near coasts.

While tides are usually the largest [[source]] of short-term sea-level fluctuations, sea levels are also subject to [[forces]] such as wind and barometric pressure changes, resulting in [https://en.wikipedia.org/wiki/Storm_surge storm surges], especially in shallow seas and near coasts.

Tidal [[phenomena]] are not [[limited]] to the oceans, but can occur in other [[systems]] whenever a [[gravitational]] field that varies in [[time and space]] is present. For example, the solid part of the Earth is affected by tides.[http://en.wikipedia.org/wiki/Tide]

Tidal [[phenomena]] are not [[limited]] to the oceans, but can occur in other [[systems]] whenever a [[gravitational]] field that varies in [[time and space]] is present. For example, the solid part of the Earth is affected by tides.[https://en.wikipedia.org/wiki/Tide]

[[Category: Earth Science]]

[[Category: Earth Science]]