Neap tides are particularly weak tides. They occur when the Moon's and Sun's gravitational forces are perpendicular to one another (with respect to the Earth). Quarter-moon equinoxes cause neap tides. At these times, the Moon is located on its perigee (closest point to the Earth), which is why these tides are weaker than average. If the Moon were at apogee (farthest from the Earth), then spring tides would be stronger than average.
If you look up at the sky during a neap tide, you will see that the rising and setting points of the Moon are directly opposite one another (180 degrees apart). This means that at any given time, only half of the Moon is illuminated. Since gravity is proportional to mass and inversely proportional to the distance between two objects, the force of attraction between the Earth and Moon is weakened by this factor of two.
At other times, the rising and setting points of the Moon are not directly opposite one another. These are non-neap tides.
The strength of a tidal wave is relative to the power of the causing body - in this case, the power of the tidal wave is reduced by a factor of four since the Moon contributes half as much mass to the total system compared with full moons.
Neap tides are caused by what? Neap tides are the weakest tides, occurring when the high tide isn't particularly high. These occur when the moon is in its first or last quarter (when we view half of its face) when the moon's and sun's gravitational pulls are at a 90-degree angle, practically canceling each other out. This leaves Earth with no significant pull from either body, causing water to pool in low-lying areas near the surface.
When the moon is full, it has both a north and south pole, so it can't push the ocean around like this. Instead, there's only one type of tidal wave called a spring tide, which occurs about every two years when the moon is at its closest approach to Earth. At these times, all the waves in all the oceans rise at the same time!
The highest tides occur during a full moon or new moon when the gravitational forces of the moon and sun are aligned head-on, giving both bodies strong influences on the sea. These are called spring tides; they occur about every two years when the moon is at its closest approach to Earth.
The lowest tides occur during a full moon or new moon when the gravitational forces of the moon and sun are at a right angle, leaving neither with any influence on the sea.
When the Moon and Sun establish a straight angle with the Earth, neap tides occur. Unlike spring tides, neap tides are caused by tidal forces canceling each other out. The result is that the gravitational pull of the Moon and Sun on the Earth are equal in strength but opposite in direction, causing the water to flow away from rather than toward them.
This occurs about every 29 days, on average. But because of the eccentric nature of the Earth's orbit around the Sun, this alignment occurs only about twice a year, so it is called an "equinoxial tide." The next one will be in January 2021.
During a neap tide, the high and low waters occur about 12 hours apart. The sea level is highest about two hours after midnight and lowest around four hours before sunrise.
The reason for this is that during the day time the Moon is pulling on the ocean and at night it's being pulled by the Sun. So there is no net change in sea level during a neap tide.
Equinoxes and solstices are important times in many cultures, because they signal new beginnings or endings of seasons, months, or years. At equinoxes the daytime and nighttime temperatures are about the same, so you would expect seasonal changes to be minimal.
When the earth, sun, and moon make a straight angle, smaller tides called neap tides develop. As a result, the sun and moon pull the water in opposite directions. Neap tides occur when there is a quarter or three-quarter moon. When this happens, the gravitational force of the moon is not aligned with the gravitational force of the sun, so they act on the water in opposite ways. This makes the tide come in and go out twice daily.
When the earth, sun, and moon form a right angle, larger tides called spring tides develop. On a day with a full moon, the gravitational forces of both the sun and the moon are aligned, so they act together to raise the ocean level high above its average value. And because both forces are acting together, the effect is greater than if either one was alone. So the ocean gets flooded with water long before a tsunami is likely to happen. After all, it takes more than just the moon to create a tidal wave!
The reason that spring tides only happen at full moons is because the direction that the earth is moving in relation to the sun is exactly perpendicular to the plane of the moon's orbit. At other times of the month, the moon is moving in a different direction, so its gravity pulls on the ocean in one direction at those times, causing tides that come in once per day.
NEAP The difference in gravitational pulls from the Moon and the Sun on opposite sides of the Earth causes the tides. Spring or neap (high) tides occur when the Earth, Moon, and Sun make a right triangle, while neap (low) tides occur when they do not. At the start of each lunar cycle the Moon is positioned so that it draws away more mass than at any other time, causing the surface of the ocean to rise until the weight of the water becomes equal to the force exerted by the Moon. As the cycle progresses, the Moon moves further away from the Earth, reducing this advantage and causing the sea level to drop.
This phenomenon was first noted by Aristotle who called it "mutton fat weather". He observed that if he put his hand into the Mediterranean Sea then it would be covered with oil but once a year when the Moon was at its closest approach to the Earth it disappeared behind a cloud bank and so had no effect. This shows that the cause of the tides is not wind but gravity! Modern scientists know that spring tides occur every 29.5 days while neap tides take place every 15 or 17 days depending on how close the Moon is sitting to the Earth at the time.
The term "tide" comes from the French word "taisir", which means "to sway back and forth" as waves do when they reach shore.
Neap tides have the shortest tidal range and occur when the Earth, Moon, and Sun make a 90-degree angle. They happen exactly midway between spring tides, when the moon is in its first or last quarter. Neap tides are strong enough to lift large boats out of the water but not tall enough to wash over the banks of rivers or beaches.
Moonset tides occur just after midnight when the moon is on the opposite side of the earth from the sun. The effect this has on sea levels is minimal but noticeable. At moonset, some areas may see land surfaces that are normally submerged at high tide exposed for a few hours. These are called "moonsets". Other parts of the world don't experience moonsets because they live near the equator where the moon always shows itself directly overhead.
Full moons bring about the highest tides of the month. Because the gravitational pull of the moon is greatest when it's closest to earth, full moons tend to cause oceans to rise higher than normal and fall lower than normal around the clock. In some places these changes can be quite significant. For example, in Newfoundland and Labrador, Canada, the average distance between land and ocean is only about 100 miles, so every full moon the island goes through a massive storm system as warm waters from the south collide with cold currents from the north.