请把这一段汉译英！

卫星

离地球最近的天体是月球。月球围着地球转，因此被称为地球的卫星。地球有一个这样的卫星，而有的其他星球有很多。　这种卫星被称为天然卫星。围绕地球转的人造太空飞船被称为人造卫星。

无论是天然卫星，还是人造卫星，都按一定路线或轨迹围着行星转动。

为什么卫星会留在轨道上？为什么他们不会被抛到外层空间？

我们可以通过一个简单的实验来解释卫星的运行。用绳子拴一块石头，绕着你的头转。如果你放开绳子，石头就不会继续转圈了。它会沿直线飞出去。

除非受到外力，在同一速度下，运动的物体总是沿直线移动。当石头在你的头顶旋转时，绳子将石头向里拉。这样石头就会做圆周运动，而不是做直线运动。使石头做圆周运动的力量就被称为向心力。

卫星沿轨迹运行，因为行星的引力将它拉进轨道中来，就像绳子使石头做圆周运动。如果没有行星的引力，卫星就不能绕着行星转，而是会抛向外层空间。

有很多人造卫星沿轨道绕地球转。有的人造卫星已经送入月球的轨道，甚至火星轨道上。第一颗绕地球转的人造卫星是俄国的“卫星一号：。美国第一颗人造卫星叫做“探索者一号”。

人造卫星可以用于各种各样的目的。根据它们的用途，我们把它们称作不同类型的卫星，比如：气象卫星用于帮助人们预报天气，通讯卫星比气象卫星位于更高的轨道，容纳了特殊的仪器，科技卫星载有科学仪器，可以收集各种各样有关太空的信息。

人造卫星发送回来的信息帮助科学家们安全地吧宇宙飞船送入太空。也创造了一个新的，令人兴奋地探索者群体—太空飞行员。

Satellite
Away from the Earth's nearest celestial body is the moon. The moon around the earth's rotation, so it is known as the Earth's satellite. The Earth have such a satellite, while others have a lot of other planets. This satellite is known as natural satellite. Around the earth of man-made spacecraft known as the satellite.
Whether it is natural satellites, or satellite, all according to a certain route or path around the planet rotation.
Why satellite will stay in orbit? Why are they will not be thrown into outer space?
We can through a simple experiment to explain the satellite operation. With a rope tied to a stone, turn your head around. If you open up the rope, stones will not continue in a circular motion. It will fly along a straight line.
Unless restricted by external forces, at the same speed, the movement is always an object moving along a straight line. When the stone in your head spins, the rope will be a stone to the lira. This stone will do circular motion, rather than doing a straight-line motion. So that the strength of stone circle is called centripetal force.
Along the trajectories of satellite operation, as the planet's gravitational pull it into orbit in the past, like a rope to make stone circle. If there is no gravity planets, satellites can not be transferred around the planet, but will be thrown in outer space.
There are many satellite along the orbit around the earth. Some satellites have been placed in the moon's orbit, and even Mars orbit. No. 1 satellite around the earth is that Russia's "Satellite One:. America's first artificial satellite called" Explorers on the 1st. "
Satellites can be used for a variety of purposes. According to their use, we call them different types of satellites, such as: meteorological satellites is used to help people to weather forecasting, communications satellites located in a higher orbit than the weather satellite to accommodate special equipment, technology satellite carrying scientific instruments, can gather a variety of information about space.
Satellite sends back information to help scientists to safely Bar spacecraft into space. Also created a new and exciting way Explorers group - space pilot.