![]() Although the Sun's gravitational pull on the Earth is 178 times stronger than the Moon's, the tidal bulges it causes are much smaller. The Bay of Fundy has one of the greatest tidal ranges on. (Not to scale.) Moon Plays the Biggest Role While both the Moon and the Sun influence the ocean tides, the Moon plays the biggest role. Figure 14.10: High tide (left) and low tide (right) at Bay of Fundy on the Gulf of Maine in North America. Whatever part of the Earth is closest to the moon experiences the most intense lunar gravity, and. The main factors that causes tides are the gravitational pull of the Moon and the Sun (Figure 14.10). When water is pulled towards the moon the tide goes up. The Moon’s mass and current distance from Earth is such that it exerts about twice the tidal force on Earth as does the Sun. The Moon orbits close enough to Earth to exert an even stronger tidal force. When the Earth is furthest from the sun (aphelion), around July 2, the tidal ranges are reduced (Sumich, J.L., 1996 Thurman, H.V., 1994). Tides are the daily changes in the level of the ocean water at any given place. Complex Strongly Modulated Tides Earth orbits close enough to the Sun to receive a strong solar tidal force. These occurrences are often called perigean spring tides. Often between 6-8 times a year, the new or full moon coincides closely in time with the perigee of the moon the point when the moon is closest to the Earth. When the Earth is closest to the sun (perihelion), which occurs about January 2 of each calendar year, the tidal ranges are enhanced. A perigean spring tide occurs when the moon is either new or full and closest to Earth. A similar situation occurs between the Earth and the sun. 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. Once a month, when the moon is closest to the Earth (at perigee), tide-generating forces are higher than usual, producing above-average ranges in the tides. Because the moon follows an elliptical path around the Earth, the distance between them varies by about 31,000 miles over the course of a month. Just as the angles of the sun, moon and Earth affect tidal heights over the course of a lunar month, so do their distances to one another. During each lunar month, two sets of spring and two sets of neap tides occur. One week later, when the sun and moon are at right angles to each other, the solar tide partially cancels out the lunar tide and produces moderate tides known as neap tides. When the sun, moon, and Earth are in alignment (at the time of the new or full moon), the solar tide has an additive effect on the lunar tide, creating extra-high high tides, and very low, low tides - both commonly called spring tides. Together, the gravitational pull of the moon and the sun affect the Earth’s tides on a monthly basis.
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