Jitender Pal
Last Activity: 9 Years ago
The moon is not the only source of tidal forces on the earth’s oceans. Although the sun is much farther away from the earth than the moon is, it is so massive that the tidal forces it exerts are almost half as large as those exerted by the moon. The sun’s principal effect is to increase or decrease the strength of the tides caused by the moon.
The near side of the earth would bulge outward toward the moon, while the far side of the earth would bulge outward away from the moon. As the earth rotates, the location of the two tidal bulges moves westward around the equator. Since a particular beach experiences high tide whenever its closest to or farthest from the moon, the full cycle from high to low to high tide occurs about once every 12 hours and 24.4 minutes. The extra 24.4 minutes reflects the fact that the moon is not stationary; it orbits the earth and completes a lunar solar month every 29.53 days. The moon thus passes overhead once every 24 hours and 48.8 minutes, rather than every 24 hours.
Twice each lunar month, the time it takes for the moon to orbit the earth, the tides are particularly strong. The spring tides occur whenever the moon and sun are aligned with one another (full moon and new moon). Twice each lunar month the tides are particularly weak. These neap tides occur whenever the moon and sun are at right angles to one another (half-moon).
Because of this interplay between lunar and solar tidal effects, the cycle of tides varies slightly from day to day. While the average cycle is 12 hours and 24.4 minutes, it fluctuates over a lunar month. That is why the atmosphere has a natural period of oscillation of nearly 12 hours