Paradise Valley, AZ

Your author is in receipt of an email attachment from two different sources, MARS.pps (413KB), predicting that on August 27 (presumably August, 2010) Mars will appear as big as the moon in the night sky. 

This bunk has been going around since 2003 when there actually was a close approach, due to the way Jupiter lined up with the sun, Earth and Mars. The exact wording of the 2003 attachment, which went viral (and now is apparently perennial), follows: "At a modest 75 power magnification (line break and new screen showing the full moon and Mars with approximately equal diameters) MARS WILL LOOK AS BIG AS THE FULL MOON TO THE NAKED EYE."

Okay, I observed the 2003 event, and I did think it was pretty spectacular. Mars was really bright. But I couldn't make out Valles Marineris or a polar cap (or any other surface feature, even a disk!) with my naked eye. 

But stop to consider what would happen if Mars did look as big as the moon. Remember high school physics, Newton's inverse-square law? It applies to gravitation as well as light. If the moon were twice as far away as it is, it would appear one-quarter its size (invert 2 and square; you get one- quarter). The same law applies to gravity. 

Imagine another gravitational field roughly that of the moon (technically, this field would depend on the mass, therefore the density of Mars with respect to the moon) in Earth's neighborhood. The least that could happen, if Mars were in the 'hood only briefly (that is if the relative orbital velocities of Mars and the earth were greatly different), would be global tidal anomalies. More significantly, the orbits of both planets would be forever altered (if you think about it, the solar system has been evolving for about 5 billion years now, so if things like this were going to happen, they would have happened by now--and indeed they did!). 

If the relative velocities of the planets were very low, they could indeed collide (it was an event like this that probably produced the moon in the first place). But if the relative velocities were just right, the planets could orbit each other, at least for a while (the moon being a loose cannon in the middle).

Okay, at least there was some truth in the original email attachment. Also, in this case, the truth will be known if August 27 turns out not to be Doomsday. It's easy to deal with this bunk; it's relatively harmless. But what about "Barack Obama wasn't born in Hawaii" or "There's no scientific evidence for global warming"? 

If people can seriously believe the bunk about Mars, what about these there's-just-no-there-there premises? It's hard to debunk the totally groundless. Believers would have to include only those who know nothing about Obama's birth and childhood (as do hundreds of people in Honolulu) or, in the other case, those who know nothing about meteorology and climatology. Just like many who enjoy magician's shows, they want to be fooled.