Mars Will NOT Look as Big as the Full Moon, But You Can Watch it Get Closer


For criminy’s sake, I just got one of those “Mars as big as the full Moon in August” emails. For one more time: this is completely false and it couldn’t possibly happen. Besides, in 2009 Mars is all but unobservable until the end of the year, and even next year it won’t be much better. So can we please see an end to these erroneous emails???

But Mars is coming closer to Earth (it happens like clockwork every 26 months) and the folks at Emory University have created a real-time distance calculator that shows Mars’ geocentric distance from us. It’s really fun to see how quickly Mars is coming closer to Earth (but pleeeeease it is not going to look as big the full Moon!!!) The distance is calculated in miles (sorry rest of the world) and shows up in blue when Mars is approaching and red when Mars begins to move farther from Earth. Very fun!

And if you need to know why Mars will not look as big as the full moon, see below.

Even at its closest approach, which happened back in 2003, Mars was 35 million miles (56 million km) away from Earth. You would have to magnify Mars 75 times to make it look as big as the full Moon, without a telescope. Mars won’t come this close again until 2287.

Here’s a graph from Robin Scagell at Popular Astronomy (below) which shows how the distance from Earth to Mars varies over the next few decades, shown as the size that Mars will appear in the sky. 25 arc seconds is about half the apparent size of Jupiter in the sky, which is the largest that Mars appeared in 2003.

Apparitions of Mars 2003-2042.  Credit:  Popular Astronomy
Apparitions of Mars 2003-2042. Credit: Popular Astronomy

Mars as big as the full moon just ain’t gonna happen, folks.

We’ve discussed the Mars Hoax email every years since 2003. Here are the UT articles for 2008, 2007, 2006, and 2005. And if you need more there are a few from Phil Plait the Bad Astronomer: here, here , here, and here’s the original one back in 2003.

And while I’m at it, I also recently got a “North Pole at Sunset” email. Another NOT.

8 Replies to “Mars Will NOT Look as Big as the Full Moon, But You Can Watch it Get Closer”

  1. Nancy:

    For criminy’s sake, I just got one of those “Mars as big as the full Moon in August” emails.

    Am I the only one who never gets such e-mails?

  2. I usually get them. It was an epidemic a few years ago, but lat year I only got one, and this year I’m still Mars-nonsense virgin.

    Perhaps because a couple of years ago I posted on my blog a rather impatient and sarcastic rebuttal of the whole thing, who knows?

  3. Sigh, I don’t get those mails either. [/pouts]

    “Please note that objects in hindsight may appear smaller than they are believed to look.”

  4. I haven’t gotten any, yet.
    Hopefully I won’t get one since I already answered these for my relatives years ago. You wouldn’t believe the other chainletter alerts I used to get. “No you did not win the lottery! it’s a scam!”

  5. I only have to comments here…

    First, when did this become this become so concerned with “Bad English” instead of “The Universe” and “Bad Astronomy”? It’s the internet…people make typos, spelling errors and often use bad grammar….git ovr it!!! If your really more concerned about spelling , then perhaps you should post on an English forum instead of in regards to passing comments about science issues.

    In relation to the article I would just like to say that very simply all the “wisdom of the world” isn’t going to stop people from believing such a thing. Just as with many of the other hoaxes and conspiracy theories that always poop up around here (intentional slip there), there are people who will always believe and/or pass on such information as this. The thing to remember here is that beyond people who tend to thrive on such rubbish and who -really- get off on perpetuating it, very simply most folks as a whole are rather ignorant, particularly about science.

    -A lot- of people are very ignorant about information on issues such as Astronomy…the majority of folks really know nothing about astronomy as a whole (and it’s easy to forget this for those of us who have developed a true passion for this field). Your “average Joe” will usually look at the night sky every now and then and think “oh…there’s the big dipper” and might occasionally catch something about the Mars rovers or the shuttles and/or ISS in the news and that’s really the extent of their star gazing or knowledge of astronomy. Unfortunately the truth of the matter is that most folks are too busy (or too lazy) to take the time to learn about things such as astronomy. For example, many times growing up my own mother would look at the night sky, see a “bright star” and say things like “My…Venus sure is lovely tonight…” and now that I know a bit about astronomy I have to honestly wonder how many times she was actually looking at Jupiter or Vega or even Arcturus! LOL!!! Of course my mother was one of those folks that believed the rumor about the size of Mars back in ’03 and was all excited about it. It’s not that my mother is “stupid” by any means but she simply has little to no knowledge of astronomy at all and a great many people are in this same boat.

    While it is frustrating, I believe that this is one of those issues like religion or astrology that “educated” people will simply have to live with for a while. When people hear about such a rumor for the first time, get excited about it and/or choose to pass it on, we will have to patiently “grit our teeth and bear it” and then politely explain it to them and -hope- that they “get it”. Yelling “When will you people learn?!?” really isn’t going to change anything at all…trust me, I feel the same way about religion! LOL!!!

    If you really want to bash someone for their ignorance and/or passing on this type of info, keep your eye out for legitimate news sources that will report or misrepresent this as a “fact”…those are the folks to take these frustrations out on.

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