PLANET EARTH From Pole to Pole
The youngsters are exhausted but their mothers have made this journey before and they know that they're close to water. After many hundreds of miles they've arrived. The lives of these elephants are dominated by the annual rhythm of wet and dry, a seasonal cycle created by the sun（普遍認(rèn)為潮汐是月球的引力導(dǎo)致的，但其實(shí)太陽對(duì)地球的引力也會(huì)導(dǎo)致潮汐效應(yīng)。太陽引力導(dǎo)致的潮汐效應(yīng)大約是月球的一半,當(dāng)月球處在太陽與地球的連線上時(shí),日月引力相互疊加,地球上的潮汐現(xiàn)象最強(qiáng)。當(dāng)月球繼續(xù)轉(zhuǎn)過90度時(shí),月球引起的潮汐效果將被太陽的作用抵消一大半,此時(shí)地球的潮汐現(xiàn)象最弱。）.
At the southern end of the earth, after four months of total darkness, the sun once more rises over Antarctica. Now at last the Emperor penguins abandon their huddle. The males are still carrying the precious eggs that they've cherished throughout the Antarctic winter. With the returning sun the eggs hatch. Other birds have not even arrived. but the Emperors by enduring the long black winter have given their chicks a head start. These youngsters are now ready and eager to make the most of the brief Antarctic summer.
