You may wonder what the moon has to do with the geography of the earth. It is the main cause of the tides in the sea. By the force of gravity it pulls the waters of the oceans towards it . The sun also does this, but being so far away its pull affects the waters less. There are other factors, such as centrifugal force, besides the pull of the moon and sun, involved in ex plaining tides, but these I must leave till you understand much more about the laws of Physics. You have , how ever , probably seen what happens to a string or wire pulled very tight . If you pluck it with your finger the string oscillates, or continues to vibrate to and fro. This is one way of making music with a stringed instrument . Now , the waters of the earth do much the same thing as they heap up and sink down as a result of the gravity of moon and sun . In general it is true to say that when sun , earth and moon are roughly in one line the pull of gravity on the waters of the ocean is greatest , and when sun , earth and moon make roughly a right angle , then the pull is least . The moon revolves round the earth roughly once every 297 days, so roughly once a month the relative positions of the three bodies will be as the sun away to the right.A little essay about moon 

 At positions B and D the earth , moon and sun are in one line , the pull will be greatest and there will be big or ‘ spring tides . ‘ At positions A and Cthe moon , earth and sun are at right angles , the pull will be in different directions and there will be small or near ‘ tides . At spring tides the sea rises highest and falls lowest ; at neap tides the rise and fall is less , and for reasons I will not explain now there are usually two high and two low tides a day .

 Where the rise and fall of a tide is along a coast in the open ocean the tide rises and falls much less than where , on a continental shelf, the shore shelves gently and the sea is shallow. Here the lower waters of each rising tide are held up by the The shallow sea bed and the waters above rise higher up and the rise and fall of the tides is greater . Sometimes the waters of a high tide flowing into the mouth of a river get held up by the river current and pile up across the river till the crest of the tidal wave falls and rushes up the river as what is known as a tidal bore . You have perhaps heard of or seen this happen ing in the Hooghly.  A little essay about moon 

Tides are important , both because they enable ships to get into harbors at high tide and because they set up currents which can keep the mouths of rivers clean of silt , or they may deposit silt , and this affects shipping , as well as changing a coast line and making lagoons , as described in Perhaps you have wondered why there are not eclipses (from the Greek meaning ‘ fail to appear ‘) of the sun or moon when there are spring tides. Of course, in position D the moon appears to be in the shadow of the earth and you might expect a lunar eclipse, but only occasionally will it be in a direct line and usually you will see the full side towards the sun lit up and it will be full moon. In position B the dark side of the moon will be towards the earth and it will be ‘ new ‘ moon. If the moon comes exactly in line with the earth and sun there will be a solar eclipse. In positions A and C you can see only half the lighted side of the moon from the earth.A little essay about moon