In what seems to be a newly-evolved form of the 15-year-old Mars Hoax people have recently been asking me about a “double Moon” that they heard is supposed to occur. I hadn’t come across it myself (maybe because I follow too much *actual* science news) but it sounded suspiciously familiar and, now being August, I figured it must have something to do with the old Mars-will-look-as-big-as-the-Moon nonsense that resurfaces every year around this time. Lo and behold there it was, in a poor Clark Kent-style disguise no less. So once again everyone: NO, Mars and the Moon will not be performing as twins tonight in the night sky—not tonight, not ever. Earth has one Moon, love it or leave it, and there will never be a natural satellite of its apparent size in orbit around our world.
(And certainly not ever the planet Mars.)
Now where did this nonsense all even come from? Gather ’round, kids…
In 2003 Mars and Earth came closer to each other than they had in over 60,000 years. This was due to an extreme case of a very natural event we call opposition and it actually happens every couple of years—most recently on July 31, 2018—because of how long it takes Mars to orbit the Sun (687 days to be exact.) But even at “extreme close range” in 2003 Mars was still about 35 million miles away…much farther than the Moon’s ~252,000 mile max distance! Still, that led somebody to casually note that “at a modest 75-power magnification Mars will look as large as the full Moon to the naked eye” which, through the telephone-game of news reporting and the popularity of email chain letters in the early aughts magically turned into “ALERT: Mars will look as big as the Moon.”
And so 15 years later here we are: still debunking this come every August (this year it started even earlier because of the July opposition.)
FACT: Based on its size Mars would have to be about 478,000 miles away to look as large as the full Moon from Earth. (Thanks to Scott from Frosty Drew Observatory.) But even at its closest possible Mars is still over 71 times farther than that. Planets, despite the Greek roots of the term, don’t just wander around the Solar System. So…ain’t no way.
What will you see? Since it’s a day and a half past full, you’ll see (weather permitting) a bright waning Moon (it’ll still look quite full-ish) rise in the southeastern sky at 8:37 p.m. (that’s Eastern U.S. time) while a bright orangish “star” (Mars) will have already been visible for a while, also in the southeast. Both will appear to move in typical fashion over the night toward the southwest…following Saturn, Jupiter, and Venus which will have already set by moonrise. Mars will look very bright just as it has these past couple of months but obviously nowhere near as large as the Moon…which makes sense as it’s almost 40 million miles away now (and getting farther.)
Image credits: Moon: Jason Major, Aug. 26, 2018. Mars: Hubble Space Telescope, July 5, 2001. Acknowledgements: J. Bell (Cornell U.), P. James (U. Toledo), M. Wolff (Space Science Institute), A. Lubenow (STScI), J. Neubert (MIT/Cornell). Credit: NASA/ESA and The Hubble Heritage Team/AURA