Sciency Words is a special series here on Planet Pailly celebrating the rich and colorful world of science and science-related terminology. Today, we’re looking at two related terms:
OPPOSITION AND CONJUNCTION
Admit it: you want to go to Mars. Despite all the radiation and sandstorms and saltwater, you still kind of want to do it. But which way is it to Mars? Bonus credit if you can point in the correct direction right now without checking a smartphone app.
Mars, like pretty much everything in space, is a moving target. Sometimes, it’s fairly close to Earth. Other times, it’s all the way on the far side of the Sun. To make life slightly easier, astronomers have special terms to describe the positions of other planets relative to Earth.
In my mind, these terms would make more sense the other way around. Mars should be in opposition when it’s on the opposite side of the Sun, don’t you think? But I’m guessing this all originates from a more geocentric view of the Solar System. Opposition, therefore, gets its name because the Sun and Mars are on opposite sides of the Earth.
What about Mercury and Venus? Since neither can be on the opposite side of Earth from the Sun, they’re never in opposition. Instead, astronomers use slightly different terms.
Of course, all this terminology can be shifted around if you want to take the perspective of a planet other than Earth. From a Venusian point of view, Earth could be in opposition or conjunction, and Martians could observe Earth to be in superior or inferior conjunction.
Knowing where planets are in relation to each other is critical for interplanetary voyages. Next week, we’ll start planning a Martian vacation, keeping an important question in mind: would you rather travel to Mars when Mars is in opposition or conjunction?
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Today’s post is part of Mars month for the 2015 Mission to the Solar System. Click here for more about this series.