The reason lies in its gravity
1. The reason lies in its gravity.
其原因在于月球的重力。
2. Because the Moon has only an eightieth of the Earth's mass,
因为月球的重只有地球的1/8，
3. it requires 97 per cent less energy to travel the quarter of a million miles from the Moon to Earth-orbit than the 200 mile-journey from Earth's surface into orbit!
因此，从月球到地球的25万英里所消耗的能量要比从地球表面进入地球轨道的200英里所耗能量少97%。
4. This may sound fantastic, but it is easily calculated.
这点听起来令人难以置信，但却很容易计算出来。
5. To escape from the Earth in a rocket, one must travel at seven miles per second.
要乘坐一枚火箭飞离地球，火箭的速度要达到每秒7英里，
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