Thursday, 17 February 2011

Lunar Lunacy

Full moon again.  Two more to go before Easter, which I am sure you know is the Sunday after the full moon after the vernal equinox.  Remember that for the next time someone asks you when Easter is this year!  It usually gets a laugh.

There is a popular urban myth that around the time of full moon hospital emergency departments are inundated with additional cases and that the outcome of major surgery is much less likely to be successful. Indeed, the term 'lunacy' is derived from this belief.

Presumably such an effect would arise from the same mechanism as the other known effects of the moon on Earth which are entirely tidal. The range of the tides is higher at full and new moon, when the Sun, Moon and Earth all line up, and this is observed as and called 'spring tides'. Spring tides have nothing to do with the season, as they happen twice every month, but the highest and lowest spring tides of the year are around the vernal (spring) and autumnal equinoxes.

The strange thing is that the alleged effects on people only occur at full moon and not at new moon.

So is it true? Or are people's observations of strange events just a case of 'confirmation bias' where they happen to notice that the moon is full when some other notable event happens. On other occasions the moon is less obvious in the sky and they don't make a link to a moon that is slightly more or less gibbous than yesterday. The subject has been extensively studied and no correlation has been found.

Of course this is not a great surprise as the gravitational (tidal) forces from the moon are incredibly small. A mother holding her baby has a gravitational effect on the baby 10 million times greater than that of the moon on the baby.



Out of interest, the French word 'lunatique' means 'is affected by the moon' or 'suffers from mood swings' and not 'is insane' although you can see the connection a little.

I do notice that particularly sleepless nights tend to coincide with the full moon, and without knowing that it is one, as in giving up on sleep, opening a shutter and thinking 'aha'. But this could of course be sheer coincidence?

Plasma Engineer said...

Not coincidence so much as confirmation bias perhaps. :)