When Science and Simple Common Sense Part Company

It happens more often than most people may realise.

Here’s the most recent case i’ve been looking at.


We all know the moon is the main cause of our ocean tides – right? Most people associate the phases of the moon with the special highs and lows of the water on our ocean shorelines and river estuary’s. Fishermen especially.

Science confirms this by stating that the moon exerts a gravitational pull on the water between it’s centre of mass and that of the Earth’s (which pulls all water towards it’s centre of mass, which is why all water flows ‘downhill’ – that is, closer to the centre of the Earth). If you look into the science a little deeper it will also say the same is true of the land of the Earth as well (being pulled towards the moon so that the Earth’s shape is lengthened slightly along a line between the two centre’s of mass!), and also that, besides the moon, all other bodies in our solar system exert a gravitational pull on us, just as we do on them. But as far as tides go – it’s the moon doing most of it… or so most think!

Most are wrong! The force the moon effects upon us is dependent upon two main things: The mass of the moon and the distance it is away from the Earth. Basically if the moon was twice as massive the pull would be twice as great but if the moon was twice as far away the force would be only a quarter as much. Science can show us that the force complies to the formula (simplified for convenience) Force = mass / (distance x distance).The force is proportional to the mass of the object doing the pulling and inversely proportional to the distance squared of said object.

Comparing the Moon and Sun, the Moon is roughly 390 times closer to us than the Sun is, meaning the distance factor makes it’s pull 152000 times stronger (pound for pound!). What everyone seems to forget however, is that the Sun’s mass is 24 million times that of the Moon so it’s force is a net total of 160 times greater than the Moon’s attraction (F(relative sun/moon) = m diff/(d diff x d diff) or 24000000/152000 = 160 approx).

If the Moon was not there we would still have tides caused by the rotating Earth showing a changing face to the Sun every 24 hours.

So it’s just simple common sense that if the Sun’s gravitational pull is 160+ times stronger on Earth than is the Moon’s then the primary cause of our tides is the Sun and not the moon – right?

Sadly, that’s just wrong! Remember above where i said most were wrong (about moon/tides)? I was leading you down a phoney trail. Although the data and results are all true the conclusion is false!

How can that be? It’s because what actually causes the tides is not simply just the force from the distant object but the difference in the force on either side of our planet (towards and away from the moon/sun/planet). Because the water on the away side is being pulled less strongly than the water on the towards side, by reason of the greater distance apart.

Georgia State Univ, Physics and Astronomy Dept.

(The other non-obvious fact about tides is that high and low tides occur, not on opposite sides of the planet (180 apart) but at 90 degrees to each other. A high tide occurs on the opposite side of our planet to a high tide while a low tide occurs opposite a low one, each are always at right angles, relative to a line from the Earth to the Moon (or whatever object is pulling the tide) to the other tide (ie. they differ by 90 degrees of longitude)).

Now because the Sun is so much further away from the Earth than is the Moon the difference between the force of the Sun on the two sides of the planet is proportionately a lot less than for the moon (roughly 40% of the moon effect).

So the science of tides tells us that the moon contributes roughly twice as much to them here on Earth as the Sun does, even though the Sun’s pull on the Earth is 160 times stronger than is the moon’s. Accordingly it IS the moon that most affects our tides (with the greatest effect being when the Earth, Moon and Sun are all in the same straight line between their centre’s – Full Moon and New Moon, new being the strongest of all).

Finally, there are secondary highs and lows which occur when the Moon is significantly angled away from the Sun.

neap tides


But then we have also to bear in mind that both the Earth and the Moon do not always keep the same distance apart from each other and both vary in distance from the Sun during the course of a month or a year. And that is before we start to worry about the effects of continents blocking the passage of water around the Equator or coastlines and bays concentrating or re-directing the ‘bulging’ water as it follows the Moon or Sun’s pull.

Let’s just say : “It’s Complicated” (massive understatement).

So, now i have given both the science and the common sense behind the topic, perhaps someone could explain the actual observations which appear to make a nonsense of everything i just said?

Observations like, in Hawaii (chosen for it’s having the least possible interference from seabed or coastal shoreline effects upon it’s tides) when a tide was at it’s peak and you should expect the moon was therefore close to being directly above the islands and so pulling the water up to it’s highest level (high tide), the moon was just rising over the eastern horizon, placing it more directly above Jamaica and the Caribbean?

Observations like, my local tides, over a one month period, show there to be high tides mostly during daylight hours and low tides consistently around sunset? This is in spite of the fact that the moon is in a different place in the sky at the same time of day for each of the 28/29 days of the moon cycle? (Or to put it more clearly – when the Sun is setting on the Western horizon, the ocean by my home is being pulled to it’s lowest point for pretty much the whole lunar month while the moon goes ‘full circle’ ?)



One comment

  1. Interesting explanation, Love – and your graphics underscored perfectly. I was expecting something quite different when I read the title – nice break from my focus on medical and cognitive science.

    Here in essentially land-locked Cincinnati, I rarely think about the tides – whereas when I lived in Florida as a kid I had daily reminders. Fun to recall those days. Thanks!
    (Madelyn Griffith-Haynie – ADDandSoMuchMORE dot com)
    ADD/EFD Coach Training Field founder; ADD Coaching co-founder
    “It takes a village to transform a world!”


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