About two weeks later, when the moon is farthest from the Earth at apogee , the lunar tide-raising force is smaller, and the tidal ranges are less than average.
A similar situation occurs between the Earth and the sun. When the Earth is closest to the sun perihelion , which occurs about January 2 of each calendar year, the tidal ranges are enhanced.
When the Earth is furthest from the sun aphelion , around July 2, the tidal ranges are reduced Sumich, J. Once a month, at perigee, when the moon is closest to the Earth, tide-generating forces are higher than usual, producing above average ranges in the tides.
About two weeks later, at apogee, when the moon is farthest from the Earth, the lunar tide-raising force is smaller, and the tidal ranges are less than average. Spring tides are tides with the greatest tidal range. They occur exactly halfway between the spring tides, when the Moon is at first or last quarter. The material that follows on tides was cut from Ocean Movements section under Coastal Processes. Tides are the daily rise and fall of sea level at any given place.
The Moon has a greater effect because, although it is much smaller than the Sun, it is much closer. High tide left and low tide right at Bay of Fundy on the Gulf of Maine. The Bay of Fundy has the greatest tidal ranges on Earth at To understand the tides it is easiest to start with the effect of the Moon on Earth. As the Moon revolves around our planet, its gravity pulls Earth toward it.
The lithosphere is unable to move much but the water is pulled by the gravity and a bulge is created. This bulge is the high tide beneath the Moon. This creates a second high tide bulge on the opposite side of Earth from the Moon.
Since so much water is pulled into the two high tides, low tides form between the two high tides Figure below. As the Earth rotates beneath the Moon, a single spot will experience two high tides and two low tides every day.
The tidal range is the difference between the ocean level at high tide and the ocean at low tide Figure below. The tidal range in a location depends on a number of factors, including the slope of the seafloor. Water appears to move a greater distance on a gentle slope than on a steep slope. So when the Sun and Moon are aligned, what do you expect the tides to look like? Waves are additive so when the gravitational pull of both bodies is in the same direction the high tides add and the low tides add Figure below.
Highs are higher and lows are lower than at other times through the month. These more extreme tides, with a greater tidal range, are called spring tides. Click to view larger and see the legend. The difference between high tide and low tide is called the tidal range. The biggest tidal range is found in the Bay of Fundy, Canada where sea level rises and falls as much as 16 m 53 feet in just over 6 hours.
The smallest tidal ranges are less than 1 m 3 feet. The highest tides, called spring tides, are formed when the earth, sun and moon are lined up in a row. This happens every two weeks during a new moon or full moon.
Smaller tides, called neap tides, are formed when the earth, sun and moon form a right angle. This causes the sun and moon to pull the water in two different directions. Neap tides happen during a quarter or three-quarter moon.
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