Do people behave oddly when the moon is full?

This sort of thing has been reported anecdotally many times, and words such as lunatic and lunacy are all supposed to refer to moon-related madness. However, careful studies have shown that there is no statistically significant correlation between odd behavior and the full moon.

People behave oddly at all times, but if they do strange things when there is a full moon, then we notice it and remember it. It might also be that in olden times one would never notice someone out at night unless the moon was illuminating things.

It has been suggested that tidal forces -- at their strongest when there is a full moon and the gravitational effects of the sun and moon add together -- might be somehow affecting the brain and causing erratic behavior. However, the combined tidal effect of the sun and moon is similarly large during a new moon. In addition, a quick calculation of tidal forces shows that the lunar effects on a human brain are more than 10 million times smaller than the tidal forces caused by our own planet Earth. It is perhaps important to point out that all of these tidal forces are tiny -- the tidal force on a human brain at sea level is significantly less than the weight of a mosquito!

At full moon, it is sometimes so bright at night that one is unable to get a full night's sleep. So sleeplessness might be making a contribution to perceived erratic behavior, too.

Dr. Knowledge is written by physicists Stephen Reucroft and John Swain, both of Northeastern University. E-mail questions to drknowledge@globe.com or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.