I was watching a really bad Japanese sci-fi movie in which the writers employed a frequent plot device. The Earth had a twin planet opposite the sun which made it undetectable to earthlings. This, of course, would be possible if the Earth's orbit was a perfect circle, which it isn't. It is, of course, elliptical. Question: Given that the Earth's speed in it's orbit varies according to its distance from the sun, would a planet opposite the Earth always maintain its position behind the sun?