Two Moons: An extremely close visit from Mars on 27 August

Way-back machine: This post was originally made on 13 Jul 2007 on
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I recently received the following eMail …

*Two moons on 27th August 2007*

*27th August; the day the Whole World is waiting for ……

It will look as large as the full moon to the naked eye. This will cultivate on Aug. 27 when Mars comes within 34.65 Million miles of earth.
Be sure to watch the sky on Aug. 27 12:30 am. It will look like the earth has 2 moons.
The next time Mars may come this close is in 2287.

Share this with your friends as NO ONE ALIVE TODAY will ever see it again.

Planet Mars will be the brightest in the night sky starting August.

First of all, if the extra bold, underlined text wasn’t a good hint, this is definately an urban legend.  My reply was as follows … I thought I’d share with the broader world …

Mars will appear as large as the full moon on 27 August 2006, or 2007, or is it 2008?
This is not true.
There are some truths to this eMail though, the next time that mars will be this close (or closer) will be in 2287.
There are a lot of fallacies though:  To start; this event DID happen in August 2003 when Mars was closer to Earth than it has been in thousands of years.  “Funny,” I hear you say, “I don’t remember seeing two moons?”  Well, very bluntly, it was not that large.  The original eMail which travelled the web in 2003 said that Mars would look about the same size as a full moon *IF* the red planet was viewed through 75X magnification telescopes.  Even through the binoculars which I used in 2003, the planet had a distinct size and shape (to me with my cheap binocs it appeared slightly bigger than a pink speck on the lense).
For those of you who are impatient, Mars does come kinda close every two years and in December 2007 it will be close enough for NASA’s next mission to the red planet.  It will not appear (to us non-astronomers) too much different than it is every day.  Mars only makes much closer passes every 15 to 17 years, so those of us around in 2018 will get a good view (still not quite as good as it was in 2003).  Keep in mind that your great-great-somanymore”great”-grandchildren will see what we saw in 2003.
But how big is the full moon?  How big did you think Mars would be?  Try this thought experiment … first read the first 4 instructions.
  1. Close your eyes
  2. Imagine a full moon (generally, an open field at night is a good start, no trees, just silver-shaded hills with the wind silently rippling through the long grass … if you are a sea-lover, replace the hills with silver-laced waves).
  3. Picture the moon low on the horizon, it must be a full moon.
  4. Once you have a clear idea of how big the moon is, return to this eMail.
  5. If your picture was clear, you can easily continue to picture the size of the moon.  “Project” this picture on a blank wall in front of you.
  6. Imagine you have something in your hand (or put something in your hand). Stretch your hand away from your face as far as you can in front of you.  Does your flat hand cover the moon?

How big is the thing which can cover the moon that you see?  A dinner plate?  A serving tray?  The bottom of a coffee cup?

In actual fact, you can cover the whole full moon with the end of your smallest (pinky) finger.  You can try this experiment in real life, all you need to do is remember to take your pinky finger with you on the next full moon.  😉
In case you’re not sure, here is a schedule of Full moon dates which will help … (notice that one is near 27 August – so if you have set a reminder to see the gigantic Martian approach, you can use it to test this “size of the moon” theory).
30 Jul 2007
28 Aug 2007
26 Sep 2007
26 Oct 2007
24 Nov 2007
24 Dec 2007
Why do we think the moon is so much larger?  Mostly Hollywood and a little childhood storytelling.  It is a romantic image.  Perhaps some of you will find it more interesting to explore the psychological factor; why we deceive *ourselves* into thinking there is a giant moon in the sky.  Many of you will just laugh this off as a crazy idea (or crazy lies).  But fortunately it is science, so it can be verified via experiments measuring fact rather than non-scientific suppositions reinforcing assumptions, opinions and beliefs. (speaking of beliefs, how big is Heaven? the book of Revelations tells us that heaven – the New Jerusalem on the New Earth – is exactly 12000 furlongs on all sides – a cube which would fit inside the moon with lots and lots of room to spare … but don’t trust me, look it up here Revelations: KJV online or open your bible to Revelations 21)
There is a lot of misinformation travelling around the internet, hopefully you find this information interesting enough to send it on and perhaps squash the misinformation.
And please, remember not to paraphrase this, try to be accurate; somebody left out “75X magnification” in the previous message and somehow it became urban legend about an amazingly huge planet which would threaten our existence.  This eMail has the words “Heaven”, “Science” , “Moon” and “close” so perhaps some day this will become “Scientists are close to discovering Heaven on the Moon”.

Do we see accurately?  Can we trust our eyes?  In fact the answer is “No”.  The human eye has about 160 blind spots around our field of vision which are all the size of the full moon.  Why isn’t our vision spotty? Our eye moves all the time in tiny amounts to get a peak at the blind areas, When we are not directly looking at the blind spots, the brain fills-in a best-guess of what is there.  That is how optical illusions work (and op art).  Here are some examples …

All this info (including the full moon experiment) is from the book “The Science of Discworld” By Terry Pratchett, Jack Cohen and Ian Stewart.

~ by James on 13 July 2007.

2 Responses to “Two Moons: An extremely close visit from Mars on 27 August”

  1. Well, I got up and look up into the sky at about half past twelve.Unluckily, it was a cloudy night and I couldn’t see anything.
    I wish to see it because it is one of the most interesting thing in my life!!!

    • I’m not sure what it was you got up early for and you were expecting to see Timmy? The effect that Mars would look like another moon is a hoax as described above. If, instead, you were looking for a full moon recently, there isn’t one at the moment and the next full moon will return on 4 October 2009. If you would like to test the size of the moon, you don’t have to view it at exactly the moment of the full moon, you can still view the close to full moon one or two days before or after.

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