When their orbit eccentricity or inclination are near zero, some problems may occur when the GPS Keplerorbit elements fitting method is applied to fit their broadcast ephemeris parameters.
As Kepler showed, the Earth's orbit is an ellipse, with the sun at one of the two focal points.
开普勒曾表明，地球的轨道是一个椭圆，这个椭圆有两个焦点，太阳在其中一个上。
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Kepler went on to show that an elliptical orbit is sufficient to explain the movement of the other planets and to devise the laws of planetary motion that Newton built on.