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What’s true – and false – about the March 19, 2011 supermoon

The moon did not cause the 8.9-magnitude Japan earthquake and subsequent tsunami on March 11, 2011. But the moon might cause high tides, and floods, on March 19.

The massive 8.9-magnitude earthquake and deadly tsunami in Japan has made the story about the supermoon coming up on March 19, 2011 even more difficult to explain. A “supermoon” did not cause the Japan earthquake, but – if bad weather combines with high tides along coastlines – it might cause flooding on March 19. Here’s what’s true – and false – about the supermoon on March 19.

This image is very exaggerated, but the moon's distance from Earth does vary. The difference between the moon's closest and farthest distance to Earth is about 50,000 kilometers, or about 30,000 miles. That's in contrast to the moon's average distance of about 384,400 kilometers. On March 19, the moon will be close. On March 11, the moon was not particularly close. Image Credit: NMSU

False: “The Japanese earthquake on March 11 is an example of a supermoon causing earthly effects.” This is not true. In fact, the March 11 moon shows exactly the opposite, since the moon is not particularly close to Earth on March 11, nor is it full or new moon (aligned with the sun and Earth). In fact, the moon on March 11 is close to first quarter – at a right angle to the Earth/sun line. Thus – according to the supermoon-earthquake connection theory – the moon’s effect on earthly water and solid rock tides should have been at its least on the day of the Japan earthquake.

False: “The last times the full moon was at perigee was in 1955, 1974, 1992 and 2005.” Not so. Full moon and perigee closely realign more often than that – in periods of a little more than 413 days (about 1 year 1 month and 18 days). Check out this list of perigee full moon distances. There are, of course, differences in how closely the full moon aligns with the moon’s closest point to Earth for the month. On March 19, 2011, there is about an hour difference between the full moon and perigee. On July 21, 2005, the difference was about 9 hours.

False: “A supermoon caused the December 26, 2004 tsunami in Indonesia.” It did not. We all remember the devastating earthquake in the Indian Ocean on that day. It created a tsunami that plowed into coastlines and caused the deaths of more than 200,000 people. The December 2004 tsunami was especially deadly along the coast of Indonesia. In terms of loss of life, it was the worst earthquake and worst tsunami in recorded history. There was a full moon that day, but it was not a supermoon. In fact, the moon on the day of the 2004 Indonesian tsunami was nearly at its farthest from Earth. The moon was closest two weeks later on January 10, 2005.

True: Some astrologers and even astronomers are using the term supermoon to describe the March 19, 2011 full moon. What makes it super is that – on the day of the March 2011 full moon – the moon will also be closest to Earth for the month. The March 19 full moon will be 221,567 miles from Earth, in contrast to the moon’s average distance of about 239,000 miles. No full moon will be this close to Earth again until November 14, 2016.

The moon is full every month, and – over the course of every month – there is a connection between full moon and earthly tides. At full moon, the sun, Earth, and moon lie more or less along a line in space. At these times, the gravity of the sun and moon are reinforcing each other. That’s why, every month around the time of full moon, people along the coast experience maximum high (and low) tides known as spring tides. Actually, there are two spring tides each month, one at full moon and the other at new moon, as shown in the illustration below.

What does this mean for the March 11 moon. Nothing at all. On March 11, 2011, the moon is not particularly close to Earth, nor is it aligned with the Earth and sun.

As the moon orbits Earth, its gravity works with or against that of the sun to create the month's highest and lowest tides, called spring and neap tides. Because water has a momentum of its own, the actual spring and neap tides lag a day or so behind the moon phases. (Wikimedia Commons)


Where did the term supermoon originate?

I had never heard the term supermoon. According to AccuWeather blogger Mark Paquette the term supermoon originated on the website of astrologer Richard Nolle. Paquette said in early March that a new or full moon at 90 percent or more of its closest perigee qualifies as a supermoon. That makes the March 19 full moon a super supermoon, because the crest of the moon’s full phase comes within an hour of the moon’s closest point to Earth.

A word about the tides

There are typically two high tides and two low tides a day. The difference in height between high and low waters varies in a two-week cycle. Around each new moon and full moon, the sun, Earth, and moon arrange themselves more or less along a line in space. Then the moon’s pull on the tides increases, because the gravity of the sun reinforces the moon’s gravity. At such times, the tide’s range is at its maximum. This is the spring tide: the highest (and lowest) tide. Spring tides are not named for the season. This is spring in the sense of jump, burst forth, rise. So spring tides bring the most extreme high and low tides every month, and they happen around full and new moon.

Halfway between each new and full moon – at the first and last quarter moon phase – the sun and moon are at right angles as seen from Earth. Then the sun’s gravity is working against the gravity of the moon, as the moon pulls on the sea. This is the neap tide: the tide’s range is at its minimum.

There is about a seven-day interval between spring tides and neap tides.

Supermoon and disasters

The March 19, 2011 full moon is a close one. That’s absolutely true. A close full or new moon does connect – regularly, frequently, cyclically – with greatest tidal maximums and minimums known as spring tides. That is also true.

However, the March 11, 2011 earthquake and tsunami in Japan occurred when the moon was near first quarter, and not particularly close to Earth. March 11, 2011 should be a time of neap tides – or least tidal range – not at a time of high spring tides. The March 11 moon is not an example of a supermoon.

I first heard about a possible connection between a supermoon and earthly disasters from a website called Psychic Connection. It predicted “severe weather patterns, increased seismic activity, tsunamis and more volcanic eruptions than normal.”

In my 40 years of writing about the sky, I’ve never heard of a connection between full moons and severe weather. Can’t comment on that one.

There are mentions in the scientific literature of a possible connection between full moons and geologic activity. The moon does indeed cause tides in the solid body of Earth, just as it causes ocean tides. So it’s logical to assume an especially close full moon might cause geologic activity to increase, and occasionally I’ve seen random (dare I say “fringe?”) study suggesting this connection. In reality, is the connection between the moon and geologic activity a strong one? I’ve never seen a study showing a striking pattern between close full moons and increased geologic activity. The Japanese earthquake on March 11 is not an example of this, since the moon was not particularly close on March 11, nor was it full or new (aligned with the Earth and sun).

So let’s hear the bottom line. Will the March 19, 2011 full moon – which coincides with the moon’s closest point to Earth – bring more earthquakes and tsunamis? Will it cause volcanic eruptions? Let me ask another question first. Why, I wonder, do people believe in unfounded predictions of disasters?

The moon’s distance from Earth is changing continually. The full moon on March 19 will be a close one, but there’s no scientific evidence it will cause any of those events. The March 11 moon does not prove the supermoon-earthquake theory. In fact, it disproves it. Plus we know of closer full moons than the March 19 moon that did no harm.

Will the March 19, 2011 close full moon cause floods? Yes, that’s different. Now we’re on more solid ground.

True: The March 19 supermoon has the potential to cause coastal floods, if it is combined with bad weather in a given location. This isn’t just true of the March 19 supermoon. It’s true of every supermoon – every full moon closest to Earth – which, as we’ve just seen, happens about every 1 year, 1 month and 18 days. Close full moons do cause maximum tidal ranges. So if a storm moves into a coastline on the day a full moon is closest, it can cause flooding along that coast. If you live along a coast, and a storm is heading your way on or around March 19 … expect possible flooding and take precautions.

I don’t believe science knows everything. Clearly, it doesn’t. But we live in a complicated world, a world that features gobs of misinformation flying willy-nilly on the Interwebs, terrifying people at every turn. So – I believe – it’s important to separate fact from fiction. The March 19, 2011 supermoon is interesting, but it’s no reason to think that more earthly disasters are looming on the near horizon. Better to focus instead on what’s really important now – looking to the reality of the March 11, 2011 8.9-magnitude earthquake in Japan and subsequent tsunami in the Pacific – and responding with our hopes, prayers and support.

Understanding moon phases

Deborah Byrd

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