R-P-R - Second Reading of Article

UNESCO Courier tides article--Second Reading

The red text below shows what I remember after my second reading of the first two paragraphs. 

UNESCO Courier, Feb 1986 p9(1) <!-- Title:Time and tide. --><!-- Journal:UNESCO Courier --><!-- Pi:Feb 1986 p9(1) --><!-- SFX: --> Time and tide. Full Text: COPYRIGHT 1986 UNESCO Time and tide, the periodical rise and fall of the waters of the ocean, are due to the gravitational pull of the moon and, to a lesser extent, of the sun. At most seaside places there are two tides a day, the average time interval between two successive high waters being twelve hours and twenty-five minutes. When the moon is directly over any point in the ocean, it pulls the water towards it causing a "doming up" of water under the moon. On the side of the earth opposite to this point, however, the centrifugal force generated by the rotation of the earth will exceed the attractive pull of the moon, causing the water of the ocean to tend to dome outwards. Thus high tides will occur at the same time on opposite sides of the earth, rather than a high tide on one side and a low tide on the other. The tides occur every twelve and a half hours due to gravity.  Most of the gravitational pull comes from the moon.  On the other side of the earth from the moon, the centrifugal force (what is centrifugal?) causes the ocean to bulge out, causing a high tide on both sides of the earth.  Low tides occur at points ninety degrees away because water is flowing away from these areas towards the areas of high tides. In other words, there is a horizontal flow from every point of the ocean towards the points directly under or directly opposite the moon. The gravitational pull of the sun, which is less than half that of the moon, somewhat complicates matters. When there is a new moon, the moon is situated between the earth and the sun so the attraction of the sun and the moon reinforce each other. Two weeks later, when the moon is full, it has moved round to the opposite side of the earth to the sun so that the earth is between them and once again they are pulling on the ocean, this time in opposite directions but along the same axis. At these times the earth experiences its highest tides, commonly known as spring tides. At the quarters of the moon, when the sun and the moon are at right angles to each other in relation to the earth, their respective gravitational pulls tend partly to counteract each other. At these times the tides, commonly called neap tides, are neither so high nor so low. The moon travels in an elliptical orbit in relation to the equator, swinging back and forth over the northern and southern hemispheres. In some parts of the earth this inclination of the moon's orbit, coupled with the fact that the axis of the earth is tilted in relation to its orbit round the sun, produces diurnal tides (tides occurring at intervals of twenty-four hours and fifty minutes) rather than the semi-diurnal tides (tides occurring at intervals of twelve hours and twenty-five minutes) described above. Semidiurnal tides predominate in the Atlantic, whereas diurnal tides are found on the coasts of Alaska, the Philippines and China. Mag.Coll.: 34D5946

Article A4118354