Mars will be as large as the Moon

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The facts about the Mars approach of 2005

Word is spreading fast. You may have read or heard any, or all, of the following:

  • "The Red Planet is about to be spectacular."
  • "Earth is catching up with Mars [for] the closest approach between the two planets in recorded history."
  • "On August 27th... Mars will look as large as the full moon."

Only one-third of those statements are true. The first one. Mars will be spectacular but not because it will be so close that it will look as large as the full moon. That last statement has some obvious mistakes. First, if Mars were ever to get so close as to look like the Full Moon, the Earth's tides would raise terribly due to the affect on Earth's gravity. Second, the August 27th date listed relates to the Mars opposition of 2003. Mars will be closest to Earth in October of this year. The orbit of Earth and Mars brig them together a little over every two years. When the orbit of Earth and Mars brought them close together in 2003, it was the closest they've been in some 5,000 years and will be in some 60,000 years. This year's approach will bring them around 69 million km, which is still impressive in astronomical terms.

As for the "large as the full moon" statement, I found out how this bad information came to be. It's the old "telephone game". As the information is being passed around it is being misinterpreted. Here's one source of the text about the Mars approach:

"At a modest 75-power magnification Mars will look as large as the full moon to the naked eye."

What seems to have happened is people, including newspaper editors, took that last part of the second sentence and ran with it. If you add in the first part of the sentence and interpret the "75-power maginification" part to mean a telescope is being used, or high powered binoculars, what is really being said is:

"When looking at Mars through a telescope at 75x maginification, it will look as big as the Full Moon does to the naked eye."

Here's another example from a news source that took this sentence

"At a modest 75-power magnification Mars will look as large as the full moon to the naked eye."

and it was editted to read:

"It will attain a magnitude of -2.9 and will appear 25.11 arch seconds wide, at a modest 75-power magnification.
Mars will look as bright as the full moon to the naked eye and will be easy to spot."

For the real facts about the size of Mars this year and helpful observing tips, check out The 2005-2006 Apparition of Mars by Jeffrey D. Beish of the Association of Lunar and Planetary Observers (ALPO).