Simple question, simple answer, right? No. Take a look at the photo below (planets are not in scale, distances are):
Earth appears closest to Mars, right? Well, it depends at which point in their respective orbits you measure their distance. Furthermore, as CGP Grey points out, the trajectory of a planet’s orbit has a huge impact on its relative distance to other planets. And for this reason one should ask not which plant is closest to Earth, rather which planet, on average, is most closest to Earth.
