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Mars's Iron Grip

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The diagram above can be used as a simple method for drawing earth's mean orbit from Mars. Draw a square and mark the centres of the sides; next put circles centred on every corner of the square sized so that each touches its neighbour at the centres of the sides of the square; then put one circle around the whole figure and another inside (shown in heavy line). To draw the relative orbits of Earth and Mars find the centre of the radius of the circumcircle and draw a circle with diameter equal to this radius so that it spans from the centre to the edge of the circumcircle. This is Mars' mean orbit. Earth's mean orbit then is taken from the same centre and just touches the small incircle (heavy line). The accuracy is 99.8%.  