The earth revolves around the sun in the speed of 30 kilometers per second, around the sun takes 365 days to five forty-eight 46 seconds, there is just one year, called the tropical year on astronomy. The earth revolves around the sun's orbit is an ellipse, the long diameter and short diameter difference, can be approximated as a perfect circle. The sun was a focus of the ellipse, and the focus is not on the ellipse center, so the distance between earth and the sun is sometimes a bit closer, sometimes a little farther. At the beginning of the January, the nearest to the earth, 147100000 kilometers, it is called perihelion. Seven early Earth farthest from the sun, is 152100000 kilometers, it is called aphelion. In fact, when the earth is at perihelion, the northern hemisphere winter, the southern hemisphere summer at aphelion; when, the northern hemisphere summer, the southern hemisphere winter. This shows, the changes of the seasons and the perihelion and aphelion independent
One interesting property of the continental and oceanic crust is that these tectonic plates have the ability to rise and sink.This phenomenon,known as isostacy,occurs because the rust floats on top of the mantle like ice cubes in water.When the Earth is crust gains weight due to mountain building of glaclation,it deforms and sinks deeper into the mantle.If the weight is removed,the crust becomes more buoyant and floats higher in the mantle.
陆壳（大陆地壳）和洋壳（海洋地壳）有一个有趣的性质，那就是这些构造板块会上升和下降。这种现象，被称为地壳均衡。它的发生是因为地壳漂浮在地幔上面，犹如冰浮水中。当陆地因为冰川作用下山脉增重时，大地会变形并且更深地陷入地幔。如果这重量消失，地壳会变得更轻快而在地幔中浮得更高。
地理
geography
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伊利运河是第一个国家重要水道始建于美国。它穿过纽约布法罗在伊利湖边特洛伊奥尔巴尼在哈德逊河逆流而上。它连接大湖和大西洋。运河担任路线,工业产品能流到西部,和材料可以涌入东。伊利运河帮助纽约发展成为全国最大的城市。
建造这条运河是支付全部由纽约州的。它花费$ 7 143 789,但很快就取得了它的价格多倍。1825年,当运河之间是打开的,和1882年,当过桥费(过运河费),国家停止收集$ 121 461 891。
一百年前,人们建造了伊利运河已经谈论了可加入大湖和大西洋。这个男人进行计划伊利运河,通过这项计划是德李天元克林顿。那些反对运河笑称它为“克林顿的沟(沟)”。克林顿喋喋不休,写了一篇关于运河和拟定计划。他和州长莫里斯去华盛顿在1812年寻求帮助的运河,但他们都unsuccessful. w.w.w.k.s.5.u.c.o.m
克林顿成了纽约州州长在1817年,不久,7月4日,打破了地1817年,纽约在罗马的运河的第一部分的运河终于在1820年。作为运河长,沿着它的课程发展城镇。巴拿马运河的长度是363英里。
