eccentricity of earths orbit 地球轨道的偏心率
BBC Orbit Earths Extraordinary Journey 非凡旅程
Orbit - Earths Extraordinary Journey 寰宇轨迹地球公转与自转 ; 寰宇轨迹
A little bit of change in the Earths orbit.
地球轨道发生轻微变动。
Some believe its risky to alter Earths orbit, while others fear the jump will make the Gregorian calendar obsolete because of the length of Earths new orbit.
有些人认为改变地球轨道太危险，其他一些人则担心由于这一跳会使地球轨道变长，所以要改写公历。
Another key purpose that our moon serves is that its gravitational force stabilizes earths axis with respect to earths plane of orbit around the sun.
月球也有另一个主要功用：它的引力使地球的轴心跟地球绕太阳运行的轨道平面保持一定的倾斜度。
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