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Don't fall for the old Mars mix-up

It's prime time once again for e-mails that claim the planet Mars will loom as large as the full moon. Should you believe the claims? This year in particular, nothing could be farther from the truth.

The Great Mars Hoax tends to turn up every August, sparking questions like this one from Moe Rickett:

"I read recently that a planet will be orbiting the earth that hasn't been this close in over 2,500 years and would be very visible to the naked eye. Could you provide me a little insight as to which planet this will be and about what time of the year to expect a good view of this event? ... I seem to think it was to be in a very close orbit to earth and it would be the first time in thousands of years it has passed this close, and will not do so again for another several thousand years. Can you please help me with this information so my family and I can view this phenomenon?"

The bad news is that none of the planets is due to have a history-making close encounter this year (although it's a notable year for Neptune). The good news is that Mars and other planets such as Venus, Jupiter and Saturn are just as visible to the naked eye as they usually are.

Moe is most likely referring to the classic Mars Hoax claim, suggesting that the Red Planet will make the closest approach to Earth ever seen in recorded history. Some accounts say the approach will be so close that it will look as if there are two moons in the night sky on Aug. 27.

This is actually a garbled report referring to Mars' close encounter in 2003.

It's true that the planet came closer than ever before in human history on Aug. 27 of that year. But even then, Mars' disk was 75 times smaller than the moon's. That means the apparent size of the full moon as seen with the naked eye was roughly equal to Mars' size when seen through a telescope at 75x magnification. This graphic shows the true size comparison that existed seven years ago.

It will be a long time before Mars comes so close again. Aug. 29, 2287, to be exact.

This August, Mars is almost as far and as faint as it gets. The next relatively close encounter won't come until March 2012. But even now, the Red Planet can be seen with the naked eye if you look in western skies just after sunset. It's part of a celestial triangle also including Saturn and the bright planet Venus. Here's a graphic from the Jodrell Bank Observatory that puts the planetary trio in perspective.

If you have your heart set on seeing a Mars as big as the moon, check out this animation from the European Space Agency, based on time-lapse imagery captured by the Mars Express orbiter as it made a full orbital circuit. You can feast your eyes on thousands of closer views from NASA's Mars Reconnaissance Orbiter. And for more on the Great Mars Hoax, review this report from 2008 (and 2006 ... and 2005).

Clarification for 8 p.m. ET: I've rewritten the passage about the moon (as seen with the naked eye) vs. Mars (as seen through a telescope). Martin Kuttner pointed out that what I had originally written could have been misread. Thanks for setting me straight, Martin!


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