PostHeaderIcon Mars Hoax, Again Again and Again

Edited to add: The 2009 Edition of this post is up!

Phil reminded me, the Mars Hoax is coming around again.

Previously published here.

For those of you who are connected to the astronomy education world, it’s that time of year: the “Mars will be as big as the Moon” e-mail is going around again. The short answer is “Nope.”

The Beginning:
Mars and Earth regularly pass “close” to each other, but not that close. Astronomers get excited because we’re at “closest approach” or “opposition,” so our ground-based telescopes have a better view of Mars. Will you see a difference without a telescope? Not really, Mars may be a little brighter or a little redder, but it will still look, to your eyes, just like a star.

2007_08_06 5 Planets
Credit: Dan Bush
Caption: This is what planets look like to the naked eye.

This e-mail hoax started in August 2003, when Mars was actually very close, astronomically speaking. It was a mere 35 MILLION MILES AWAY. Since then, the e-mail has been going around every August, with the date slightly changed.

The Truth:
In 2007 Mars was at opposition in December, not August, and it will still be 55 million miles away. The next one after that is in January of 2009 2010. So, you’ve got a while to wait.

Here is what some scientists are saying:

Dec 18, 2007- Closest approach of Mars and Earth (0.589 AU = 88.42 million km). Apparent diameter of Mars is 15.88″ (seconds of arc). The apparent diameter of the Moon is about 1/2 degree which is 1,800″ (seconds of arc). So, will Mars look as big as the Moon? Not even close. [1 degree = 60 arcminutes – 3,600 arcsec]
-Alan Gould, UC Berkeley

The Moon and Mars could not look alike in the sky, BUT an astronomer might say that that through a telescope at 100X, Mars _through a telescope_ might look almost as big (1,588″) as the Moon to the unaided eye (1,800″). Perhaps the part of the comparison about looking through a telescope was lost, and media types looking for a hype to hang a story on ran with it. That’s the only explanation I can give about the recurring story about Mars being as big in the sky as the Moon. This story reappears at almost every opposition of Mars, especially the really close ones.
– Steve Berr

Let Them Down Easy:
So what do you say to someone who is excited? Cover each of these topics:

  • Validate the excitement
  • Point out something related that will be cool
  • Correct the misconception
  • Invite them to view/look up something real

For example:
“So did you hear about Mars being as big as the Moon?”
“Yes! I agree, that would be awesome. You know, October 2009 through April of 2010 is really going to be the best time to view Mars though, maybe we could take out a telescope together? Unfortunately, it’s still really far away, so it won’t ever look as big as the Moon. Also, if you want to see something cool sooner, let’s go out and see the Andromeda Galaxy or Jupiter this month!”

Want More?

6 Responses to “Mars Hoax, Again Again and Again”

  • Sean says:

    > Astronomers get excited because we’re at “closest approach” or “opposition,” so our ground-based telescopes have a better view of Mars.

    Why is this called opposition? If we’re at the closest point, wouldn’t that mean we’re in conjunction? (of course, I’m using these terms that I learned from astrology, so they’re probably erroneous).

  • Paul says:

    The *moon* wouldn’t even be as big as the moon, if the human eye could perceive its slow escape from Earth’s gravity. Luckily we can’t see it getting smaller.


  • Holly says:

    AGAIN? *sigh* I guess there’s (sort of) comfort in constancy? Have we gotten the call yet? At least you have a way to be proactive about it. I guess it is probably a reoccurring appointment in your calendar by now!

  • Heather says:


    I love that you do this. I just had to respond to my own daughter who was forwarded the Mars Hoax.


  • alicesastroinfo says:


    Opposition is because it is opposite the Sun.

  • mrsnib says:

    Just got it for the 1st time in 2010! I’ll let him down easy!

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