Happy Opposition Day!

Mars imaged by ESA’s Mars Express spacecraft on July 24, 2018 from about 6,000 miles.

It’s Opposition Day! No, that’s not a political stance but rather a geometric one, relating to the positions of Earth, the Sun, and Mars in the Solar System. Today our neighboring planet Mars will be directly opposite the Sun relative to Earth, which will make it the second-brightest “star” in the night sky after Venus. Since it takes Mars about two years (687 Earth days, to be exact) to orbit the Sun, this type of alignment event occurs, oh, about every two years. But this year it’s occurring when Mars also happens to be closest in its orbit to the Sun, an event called perihelic opposition. So tonight, go outside and you’ll see (weather permitting!)  a very bright orange-colored star in the southeast—that’s our neighbor Mars, just under 36 million miles away!*

Mars at opposition. Credit: MSSS

Mars will continue to be bright (and has been for several weeks, really) well into August as we pass the July 31 closest approach with Earth. That’s next Tuesday, when we’ll only be 35.8 million miles apart. (Because of slight orbital angle differences this doesn’t occur on the same exact day as opposition.) It’ll be the closest we’ve been since August 27, 2003, which itself was the closest in over 60,000 years!

(And no, Mars won’t look “as big as the full Moon in the sky.” Not today, not ever. Any news that claims that is no source worth listening to. This misinterpretation arose from the 2003 opposition where someone mentioned that Mars will look about as large as the full Moon in a telescope—which itself isn’t even remotely true, if you were to use the same magnification and field of view for both objects. It was hyperbole that got turned into nonsense.)

The next close approach will be in October 2020, when Mars and Earth will be 38.6 million miles apart.

Today also happens to bring a total lunar eclipse into view for part of the world. It will be the longest lunar eclipse of the century…but it won’t be visible from the U.S. (or the majority of North America, actually.) But if you hear about the “Blood Moon**” that’s what that is…Europe, Africa, and much of Asia are in for a great show!

*That’s 58 million kilometers, which equals about 75 round-trips from Earth to the Moon!

**It’ll still be a full Moon for North America though…actually a “mini-moon” as the Moon will be at apogee today, about 252,300 miles away.

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