Don’t Believe The Mars-Moon Story

It’s Nonsense

How Mars and Venus will look after sunset on September 27. Does Mars look as big as the full Moon to you?

So, by now, you’ve probably heard that Mars is going to look as big as the full Moon tonight. It’s a very popular Internet meme these days, sent around by people who think it sounds cool but never stop to think about the physical situation that such a story represents.

Epic fail on their part. Don’t let it be one on yours.

Think about it. How far away is the Moon?  I’ll tell you — it’s (on average, depending on where it is in its orbit) about 384,000 kilometers away from us.

Now, how far away is Mars?  I’ll tell you that, too.  When Mars and Earth are at their closest points in their orbits, Mars can be about 55 or 56 million kilometers away.  That makes it look like a reddish point of light from our vantage point here on Earth.

Okay, now compare 384,000 with 55 million.  BIG difference.  It’s a big enough difference that Mars will always, always, always appear as a point of light in our sky.  And the Moon will be brighter and bigger and look like… the Moon.

If Mars were to look as big as the full Moon in our skies, we would have BIG problems. Bigger than worrying about how it would look in our sky. Let me put it to you this way: if it were as big as the full Moon in our sky, we’d be looking for a way off-planet before the tidal forces broke both worlds apart. NASA explains it all pretty well here.

So, don’t believe the meme — don’t let some foolish person’s misunderstanding of science and planetary orbital mechanics live rent-free in your brain.

Instead, head out tonight and check out Mars and Venus after sunset. They look lovely, without all the need for breathless Internet/Web hype.


  1. Tim

    The last time I heard this mars as big as the moon story from a friend, I explained why the claim was ridiculous and convinced them it was like and urban myth.

    A few days later they missed a very spectacular lunar eclipse because they dismissed all reports about it – confusing predictions of a bloodred full moon with the myth of the moon-sized mars.

  2. Bill Keen

    Some years ago when this nonsense first came up a friend of mine asked me about it. I googled the topic and found an article, I forget where, that said “Mars will look as big as the full moon

    when viewed through a backyard telescope”

    It was formatted like that, with the qualification on a separate line. The website was roughly formatted and it would have been easy to miss the subsidiary line. I told my friend it was misreading of this report which gave rise to the idea.

  3. ccp

    I can see where that might happen, but what SIZE backyard telescope would you have to have to make Mars look as big as the full Moon? I mean, I’ve observed it plenty using a 6″ with a variety of eyepieces, and Mars never looked as big as the Full Moon would look through the same telescope. There’s a LOT missing out of that original story — poorly written at best.

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