With the recent launch of MAVEN (a spacecraft that will study Mars’ upper atmosphere), I’ve been feeling a bit nostalgic for my days as a planetary scientist. There’s no insightful analysis in this post, just a clear graph of how far Earth is from the other planets.

A seemingly simple question is, “How far away are the other planets in our solar system?” The answer is, unfortunately, not so simple; it depends on when you ask the question. Generally speaking, when a planet orbiting outside Earth’s orbit is in opposition (opposite the sun), it is closest to Earth. When that planet is in conjunction (directly “behind” the sun), it is farthest from Earth. Planets with smaller orbital radii (i.e., Mercury and Venus) are said to be in inferior conjunction and superior conjunction when they are closest and farthest, respectively, from Earth. Measuring these distances is somewhat complicated by the fact that orbits have some inclination with regard to the ecliptic, and they are elliptical. Consequently, the distance between Earth and another planet in opposition/conjunction is not always the same!

So here I’ve plotted the average opposition and conjunction distances, as well as the theoretical extreme distances. These extremes are based on aphelion and perihelion measurements for each planet, and may not, therefore, have occurred precisely (or will ever occur). But they are extremely good estimates, especially given the limited resolution of the graph, for how close/far we ever get to other planets.

Keep in mind that the relative sizes of the dots is not representative of the planets’ sizes – they are varied partly to help those who are colorblind distinguish between the red and the green, and to emphasize that a planet will appear smaller when farther from the Earth.

Data sources: http://www.calsky.com/ and http://nssdc.gsfc.nasa.gov/planetary/factsheet/