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Happy Opposition Day!

27 Jul 2018, 16:33 UTC
Happy Opposition Day!
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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 ...

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