It is May 2003 and today three planets and a central star are in a straight line (this isn’t necessarily our solar system). The farthest planet takes 18 years to complete an orbit around the central star; the second farthest takes 9 years to orbit around the star; and the nearest takes 4 years 6 months. What month and year will it be when the planets and the star are once again in a straight line? Assume they have the same axis of orbit and their calendar measurement is the same as ours.
Answer
May 2012. Given the assumption that they have the same axis of orbit, in 9 years they will be aligned in a straight line even though they are not at all on the same side of the star. The furthest planet with the 18-year orbit is on the far side of the central star, but still in line with the others.
