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Two moons on August 27th, 2007

  1. Jul 31, 2007 #1
    First off, forgive me if this should have gone in the “Astronomy Events” sticky.

    Long time reader… but hardly ever post.
    I got this email today. It actually has been going on for some time now, since 2003 I believe.

    “Two moons on 27th August 2007*
    *27th August; the day the Whole World is waiting for ......
    Planet Mars will be the brightest in the night sky starting August.
    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. “

    My question is, how much truth is behind this?
    I’ve been doing some googling on it and found this:

    “this e-mail can be traced back to 2003... and nasa had issued a notice about it saying that its a hoax..."

    Mars' radius is about 3,400 km
    Moon's radius is about 1,700 km
    So, Mars is about twice as big as the Moon.

    Brightness obeys the Inverse Square Law. So, a lamp 1 meter away from you would have 4 times the brightness if it was 2 meters away from you. Planets and Moons such as Mars & the Moon do not emit light, but they reflect light from the Sun. Which means that Mars would reflect 4 times the amount of light than the moon... right?

    So, it would look brighter but not bigger than the moon correct? It says Mars will come within 34.65 Million miles, is this correct? At that distance, Mars wouldn’t look as big as the Moon, would it? As bright, maybe… but with the Moon at 238,700 Miles away I can’t see Mars look “as large as the Moon to the naked eye”

    I'm a bit lost here… please school me :smile:
  2. jcsd
  3. Jul 31, 2007 #2


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    Mars at its closest approach is neither the size nor the brightness of the Moon.

    I'd also just like to point out that Mars comes rather close to the Earth very frequently. Even if this really is the closest approach in several hundred years (I'd have to go look that up, and don't think it's true), you'll have many other opportunities to see it when it is only a fraction of a percent further away.

    - Warren
  4. Jul 31, 2007 #3


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  5. Jul 31, 2007 #4
    You seem to have missed the inverse part. If the lamp were twice as far away, we would say that it is four times dimmer.

    The amount of light that a planet or moon reflects depends on its cross-sectional area and its albedo, or how much light it absorbs. If the Moon and Mars had identical compositions, Mars would indeed reflect 4 times as much as the Moon.

    The moon has an apparent magnitude of -12, and Mars has a max apparent magnitude of -3, which means that Mars is ~4000 times dimmer than the Moon.

    IIRC, this whole hoax originated with someone mangling the awkward statement that in August 2003 Mars would appear in a telescope to be as large as the Moon to the naked eye.
  6. Jul 31, 2007 #5


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    Mars's last opposition (Aug, 2003) was one of the closest in a while, but the next one is only going to be a couple percent further away.

    Btw, Mars is at opposition about every 2.5 years, which means the next opposiiton isn't August, but December 24. :rolleyes:
  7. Jul 31, 2007 #6


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    Oh. Em. Geeeee.

    Is this myth doomed to repeat every two years???

    It wasn't true in 2003*; it wasn't true in 2005 and it's STILL not true in 2007.

    *2003 was the origin, Mars was at its closest approach - a full 25 arc seconds across - compare that to the Moon's 1800 arc seconds.

    But Mars WAS the size of a full moon "WHEN SEEN THROUGH A MODERATELY-POWERED TELESCOPE"- which is how the original story was reported.
  8. Aug 1, 2007 #7
    Well, I thought I would post a thread here during the hoax season, but I never got around to doing it. This mail has been spamming the world since the 2003 event.
  9. Aug 14, 2007 #8
    hey guys, according to my calculations (read: celestia) Mars will be rougly 55 million miles from Earth on Dec 24, 2007. It will still be a speck, albeit a particuarly bright one.

    NASA's new mars mission is supposed to land there somewhere Spring 2008.

    Cheers :)

    edit for content:
    July/August 2018 - Mars will be 35 million miles away. In fact, if you're in the US, July 28/27 will be the best nights to see Mars + Moon.

    August 2003 - Mars was roughly 35 million away.

    As for size, the arc length is orders of magnitude difference. Certainly no scenario where you'd think there were two moons.
    Last edited: Aug 14, 2007
  10. Aug 27, 2007 #9
    Lunar Eclipse

    Thanks for the replies concerning this hoax guys.
    Mars may not be visible as big as the moon tonight, but there will be something going on in the skies early tomorrow morning. Maybe someone got confused :)

    "A lovely total lunar eclipse will be visible throughout the Bay Area and all of California before dawn Tuesday morning as the Earth's shadow darkens the bright full moon, and wherever skies are clear, it will be a time to look upward wide-eyed."
    -- The San Francisco Chronicle

  11. Aug 27, 2007 #10
    Oh boy...the Moon's going to turn red and everyone you debunked will confuse it for Mars and say "I told you so!".
  12. Aug 27, 2007 #11
    Its funny you say that because my brother just wrote me back and said... "I thought you said nothing was going to happen tonight!" lol
  13. Aug 28, 2007 #12
    thank you about this information
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