Mars hoax email
A hoax circulated by email in 2003 claimed that Mars would look as large as the full Moon to the naked eye on August 27 of that year. The hoax has since resurfaced each time before Mars is at its closest to Earth, about every 26 months.
It began from a misinterpretation and exaggeration of a sentence in an email message that reported the close approach between Mars and the Earth in August 2003. At that time, the distance between the two planets was about, which was the closest distance between them since September 24, 57,617 BC, when the distance has been calculated to have been about.
Background
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 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 than it had been since 57,617 BC, and than it will be until 2287.There was another opposition on 30 October 2005, but with a minimum distance about 25% greater than in 2003 and apparent diameter correspondingly smaller. The magnitude was −2.3, about 60% as bright as 2003.
Origin
The Mars hoax originated from an email message in 2003, sometimes titled "Mars Spectacular", with images of Mars and the full moon side by side:Although the e-mail itself is correct except for the statement that "it may be as long as 60,000 years before it happens again", 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 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.
Mars, normally never more than a dot in the night sky, could not 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 tidal and 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 about the same tidal effect.