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SYFY WIRE Bad Astronomy

No, Mars Won’t Be as Big as the Moon. Ever.

By Phil Plait

Oh, is it August already? That means itâs time for the nonsense that is the âMars will be as big as the Moonâ claims once again.

Yup. I saw this is getting spread around on Facebook:

August 27 at 00:30 Lift up your eyes and look up at the night sky. On this night, the planet Mars will pass just 34.65 million miles from the earth. To the naked eye it looks like two of the moon above the ground! The next time Mars will be so close to the Earth as much as in 2287.
Share the news with your friends, because no one living on this earth has ever seen!


Every year in August, somewhere, somehow, this silly claim springs from the cold, dead ground, rising once again to shamble across the Internet. The first time it was just a mistake, but ever since then itâs been a hoax. Simple as that.

This all started in 2003, when an email got spread around claiming that Mars would look as big as the Moon in the night sky on a specific date in August. Because I am kind-hearted, I attribute that to a simple misread of the original idea: On that date, through a telescope that magnifies an image 75x, Mars would look as big as the Moon does to the naked eye.

As far as it went, that was about accurate. Around that time, the Moon really was about 75x bigger than the red planet, so through an eyepiece, Mars would be magnified enough to look the same size as the Moon does without a telescope.

But this being the Internet, that got all mished and mashed up, and somehow became this idea that if you went outside Mars would look huge in the sky, looming over the world like something out of an H. G. Wells novel.

Once the date passed, I breathed a sigh of relief. That was that, I thought.

Oh, such naïveté ! Of course I was wrong. The email reappeared in 2005. And in 2006. And 2007, 2008, and 2009. Over the past couple of years itâs been dormant, but now itâs back once again and looking to eat your brain. When I saw it on Facebook, for example, it had 450,000 shares as I write this. Half a million people, or thereabouts, have spread this rumor. 

At least this year they added the twist of it looking as big as two Moons. Maybe they're looking for better Google SEO.

Still, this claim is even worse this year than previously. On Aug. 27, Mars wonât be anywhere near Earth; in fact itâll be on the other side of the Sun, about as far away as it can be. Despite the Facebook claim, it wonât be 35 million miles from Earth; itâll be 210 million miles (350 million kilometers), so tiny it will look like a dot even through big telescopes, with a size only about 0.2 percent as big as the Moon.

Thatâs right: The Moon in the sky will be 500x bigger than Mars, not half as big. But whatâs a factor of a thousand between Facebook friends?

If I sound a bit exasperated, thatâs because I am. This rumor started off innocently enough a decade ago, but now is clearly a hoax. And whomever starts the rumor every year must know itâs not real and is just playing a joke. I generally have no problems with good-natured pranks on the 'Net, but this one is tiresome at best and is damaging at worst. Why?

Because people believe and then go outside to find Mars. Theyâll be disappointed, which is just about the worst emotion I want people to feel about astronomy! I remember back in 2003, when this all started, astronomy clubs and observatories were packed on the fated night as people lined up for blocks to see Mars. Thing was, even at best Mars isnât terribly big through a small telescope; itâs not a large planet, and itâs a long way off. If people are expecting to see it like the Earth seen from low orbit, they wonât be happy. I had a lot of people tell me exactly that, too.

And since folks arenât all that familiar with the sky, they fall for this prank year after year. I know there are bigger things in the world (and Universe) to worry about, but this bugs me. We have enough woe and misfortune in the world as it is. Astronomy, the beauty of the sky, and the natural awe laid out before us are instead a source of wonder and joy.

Iâd prefer to keep them that way.

So instead of going out on Aug. 27 and looking for Mars when it canât be seen, instead go look for the waning gibbous Moon in the morning after sunrise. Watch Orion rise after midnight, or spy Venus shining like a beacon in the west right after sunset. Got dark skies? The Milky Way flows across the sky eponymously and gets higher overhead the farther south you are. Maybe weâll even get an aurora if you live at extreme latitudes.

The sky is wondrous, with treasures to satiate desires both subtle and gross.* Go experience the reality of it.

* With no apologies whatsoever to Q.

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