The Mars hoax was a hoax circulated by e-mail that began in 2003, that claimed that Mars would look as large as the full Moon to the naked eye on August 27, 2003. The hoax, which has since resurfaced every year from 2005 through 2012, began from a misinterpretation and exaggeration of a sentence in an e-mail message that reported the close encounter between Mars and the Earth in August 2003. At that time, the distance between the two planets was about 55,758,000 kilometers, which was the closest distance between them since September 24, 57,617 BCE, when the distance has been calculated to have been about 55,718,000 kilometers.
Both Earth and Mars are in elliptical orbits around the Sun in approximately the same plane. By the nature of the laws of physics, the distance between them varies periodically from a minimum equal to the distance between their orbits at some point along them, to a maximum when they are on opposite sides of the Sun. These minimum (opposition) and maximum distances vary considerably as the two planets progress along their elliptical orbits, and occur about every 780 days. Mars was closer to the Earth in August 2003 (at the opposition than it had been since 57,617 BCE, and than it will be until 2287 or possibly much later.
There was another opposition on 30 October 2005, but with a minimum distance about 25% greater than in 2003 (as reported in the original email, text below) and apparent diameter correspondingly smaller. The magnitude was −2.3, about 60% as bright as 2003. (The Moon has an apparent diameter of around 30 minutes of arc, i.e., 1800 arcseconds, with magnitude of about −12.7 when full, about 9,000 times brighter than Mars in the 2003 approach.)
The Red Planet is about to be spectacular! This month and next, Earth is catching up with Mars in an encounter that will culminate in the closest approach between the two planets in recorded history. The next time Mars may come this close is in 2287. Due to the way Jupiter's gravity tugs on Mars and perturbs its orbit, astronomers can only be certain that Mars has not come this close to Earth in the Last 5,000 years, but it may be as long as 60,000 years before it happens again.
The encounter will culminate on August 27th when Mars comes to within 34,649,589 miles (55,763,108 km) of Earth and will be (next to the moon) the brightest object in the night sky. It will attain a magnitude of – 2.9 and will appear 25.11 arc seconds wide. At a modest 75-power magnification
Mars will look as large as the full moon to the naked eye. Mars will be easy to spot. At the beginning of August it will rise in the east at 10 p.m. and reach its azimuth at about 3:00 a.m.
By the end of August when the two planets are closest, Mars will rise at nightfall and reach its highest point in the sky at 12:30 a.m. That's pretty convenient to see something that no human being has seen in recorded history. So, mark your calendar at the beginning of August to see Mars grow progressively brighter and brighter throughout the month. Share this with your children and grandchildren. NO ONE ALIVE TODAY WILL EVER SEE THIS AGAIN
Although the e-mail itself is correct, the hoax stemmed from a misinterpretation of the sentence "At a modest 75-power magnification Mars will look as large as the full moon to the naked eye". The message was often [laxly] quoted with a line break in the middle of this sentence, leading some readers to mistakenly believe that "Mars will look as large as the full moon to the naked eye" when, in reality, this sentence means that Mars enlarged 75 times will look as big as the moon unenlarged.
It is quite obviously scientifically incorrect that Mars, normally never more than a dot in the night sky, could suddenly become visibly large due to normal variations in orbit. If Mars did appear as large as the moon it would be so close that it would cause catastrophic gravitational effects — Mars has about twice the diameter of the Moon, and hence would be about twice as far away for the same apparent size. It has nine times the mass of the Moon, and would have over twice the gravitational effect (nine times the larger mass divided by relative distance squared).
The hoax has resurfaced a number of times since 2003, and may continue to do so, always announcing an imminent close Earth–Mars approach. The content of the original email, although almost entirely correct for August 27, 2003, has falsely been redated to announce a new close Earth–Mars approach — the real close approach was in 2003 only — also misinterpreting the original e-mail by saying that Mars will look as large as the Moon. The later e-mails are incorrect, as Mars will not come as close to Earth as it did in 2003 until August 28, 2287, or later.
 See also
- Cohen, Howard L. (2005-08-26). "Mars Hoax". Alachua Astronomy Club.
- "Mars Close to Earth". Urban Legend Reference Pages.
- Cohen, Howard L. (2006-08-26). "The Mars Hoax Won't Go Away". Alachua Astronomy Club.
- Meeus, Jean (March 2003). "When Was Mars Last This Close?" (PDF). Planetarian: 12–3.
- Beware the Mars Hoax (NASA article from 2005)
- Snopes page on the Mars Spectacular
- Hoax Slayer article: Mars, Earth - Closest Approach in Recorded History
- Sky and Telescope Magazine: Mars Hoax Returns
- space.about.com: Mars Hoax Back Again
- BBC News: The perennial Mars hoax e-mail
- 2006 Mars Hoax Powerpoint Presentation
- MSNBC Video on the Mars hoax
- MSNBC Cosmic Log