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The Weather and the Moon

For many centuries she's a source of inspiration: The Moon. A reliable beacon during the nightly hours; always makes lovers' hearts beat faster and the moon can even make you crazy -- so they say. And much more is ascribed to the moon;  according to lots of proverbs her colour and her changing phases seem to have an influence on the weather. Let's see what's the truth in all this:

Clear Moon, frost soon.  

The Full Moon eats the clouds away. 

Dark mist over the Moon is a promise of rain.  

A Red Moon is a sure sign of high winds. 

And should the Moon wear a halo of red, a tempest is nigh.  

Many rings around the Moon signal a series of severe blasts.  

When the New Moon holds the Old Moon in her lap, expect fair weather.

Sharp horns on the Sickle Moon indicate strong winds.  

The heaviest rains fall following the New and the Full Moons.

When the moon's horns point up, the weather will be dry.  

Pale Moon doth rain,

Red Moon doth blow,

White Moon doth neither

Rain nor snow. 

But let's first have a look how it all started.

The origin of the moon.

The earth and her moon are the strangest couple in our solar system; compared to the earth the moon is actually far too big. The moons diameter is a quarter of the earths' . You can equate that to Venus, which has no moon, and is almost the size of the earth. Or what about Mars? This planet has two moons, but these are no more than a couple of swirling rocks. No, moons like ours can only be found orbiting super-planets like Jupiter or Saturn.
Most of the scientists agree: moon and earth didn't evolve at the same time. The moon has its origin in a disastrous event taking place about 4.5 billion years ago; the earth was just born. At that time the other smaller planetary bodies were also growing. One of these, about the size of Mars, hit the earth. Most of the intruder evaporated, only the core fused with Earth. Lots of earths' material was blown into space; a dense ring of rocky debris went into orbit around the earth and finally aggregated into the moon. 

This sounds a fanciful and unbelievable story, but computer simulations have demonstrated that there's a big chance it happened this way.
In former days the moon and earth were much closer together, about 100.000 miles, and both rotated much faster around their axes than nowadays. 

During a very complicated game of gravity performed by Sun, Earth and Moon; the latter two drifted apart and, at the same time,  turned more and more slow around their axes. 
This process hasn't stopped yet. The distance between earth and moon still grows; about 1,4 inches a  year. But meanwhile the moon is already "stopped" by the earth; and that's why we only see one face of the moon.
In the very remote future, about 5 billion years from now, day and night will last 1,5 times longer so "the space of 24 hours"  will take 36 hours.  

The moons phases.
The moon is visible due to the sunlight. The sun illuminates the moon and that's why we can see her. As the moon turns around the earth she is not always fully visible; actually the full moon appear only when she opposite of the sun from the earth's view. The other phases appear when she in another position of her orbit. The figure will explain.

The moons gravity

Naturally the moon brings a lot of gravity to bear at the earth. You can notice when your spend a day at the beach. Two third of the tides-movement is caused by the moon; the rest is due to the Sun. Such tidal effects also take place in the earth's atmosphere, but they're hardly measurable. It's estimated that the differences in air pressure caused by tides is only
1 mbar or 1 hPa.  

The moon and the weather

And this leads us directly to the influence of the moon on our weather. For lots of people this influence is taken for granted especially when the moon is full or new. When rain's coming; my elderly neighbour always and invariably declares: "Yes, naturally, its new moon".And what's more; many weather-proverbs refer to the moon.

There are roughly two kinds of proverbs:

  • One group is about the visibility of the moon -- colour, clouds -- in relation to certain weather-conditions. 
  • The second group, and for this subject the most interesting, is about the phases of the moon and weather-conditions.

The first group: visibility of the moon 

In proverbs like: " clear moon, frost soon"  or " a red moon is sure a sign of high winds" the relation between the moon and the weather-conditions is clear. But its not the moon that's influencing the weather; its obviously the other way around; cause and effect are changed.. Naturally at wintertime there's a big change of frost during full moon. A full moon is only visible when the sky is clear. And during clear spells the radiation can be so strong that the temperature lowers below zero.  

Another factor are high or cirrus clouds developing at higher levels in the atmosphere, mainly exciting of ice-crystals. When these crystals are illuminated by the moon; sometimes a halo will appear, forming a ring around the moon;  or she loses her familiar glance. 
Cirrus clouds covering the sky often indicate a warm-front coming, associated with an area of low pressure; which means a change to more unsettled weather; with the usual rain and wind.

And then the charming picture about the new moon holding the old one in her lap. When this is the case, the proverb says, you can expect fair weather.  Sometimes in a very thin new moon-crescent; the shadow of  the whole moon is visible as an outlined grey ball; rising out of the tiny illuminated part. This visible grey moon-shadow appears when the earth reflects her sunlight on the moon. The air must be very clear and quiet; no turbulence in clouds to obscure. Its the case in settled weather-conditions; very likely an area of high pressure is around, the weather will be fair.

The second group: the phases of the moon

Its a widespread believe that the four "strategic" moon phases (new- first quarter; full moon, last quarter) can cause a break in the weather. 
In our region the weather is pretty variable and it's hard to define when you can speak about a break. 
Besides that, every seven days a strategic moon phase is there; so the changes that a chance in moon phase and a weather-break coincide is fairly big. And this certainly counts when you're not so very particular about the exact moment and the weather-break can take place a day earlier or later.

Let's concentrate on the most important proverb: " the heaviest rain falls following a new or full moon"
Meteorologists of the Dutch Meteoconsult has followed the weather conditions around new and full moon, during three days -- so a day before, during and after the moon phase. -- This research took places during 100 new and full moons; so it took over 8 years -- .  
To be short the test was this: the weather around every new and full moon got a mark in the scale from 0 to 10. A clear improvement of the weather (contrary to the proverb) got a "0" . When there was no change a "5" was written down, and a deterioration got a "10". (After all: the last situation is predicted by the proverb.) 
When the theses is right the mean of all this marks must have been high. Actually the mean was 5.1; exactly the result you can expect when the weather doesn't care at all about the moon phases.

And the one who thinks logical and down to earth, should be convinced that the moon phases can't influence the weather.
Suppose that the weather really gets worse during new - or full moon. 
A full moon in Britain means a full moon around the globe. 
It's not necessary to explain that a weather-deterioration in Britain can't also mean a depreciation in the Alps or the Caribbean or Australia.
And that the moon only would influence the weather in Britain is absolutely inexplicable. Thankfully no search to such a strange evidence is needed: it simply can't be true. There's no relation between the moon-phases and the weather.

No relation at all?

Actually the statement that there's absolute not a relation is not entirely true; but the influence is very local and limited. 
For example: Imagine coastal area's with proper sand or shoal beaches (the Wash) and a fair tidal difference during a warm sunny summer-day. There's a sea-wind;  now the maximum-temperature along the coast will be at the highest when the tide is low. The air is warmed by the sandbanks and shoals which are fallen dry and heated by the sun. The time of high- and low tides change every 24 hours about three-quarters of an hour. The maximum temperature of the day will correspond with the tides; and therefore with the phase of the moon. In this very specific case there's a relation between the moon and the maximum temperature.


With thanks to: meteoconsult, Holland


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