Kryptonite for the supermoon | Bad Astronomy
If you believe the mainstream media, you might think this weekend’s “supermoon” will cause earthquakes, volcanoes, bad weather, halitosis, dust bunnies, and hangnails.
Guess what I think of this idea! Hint: check the name of my blog. Got it? Good.
In reality, this “supermoon” nonsense is, well, nonsense. I have some details below, but for those of you who are impatient (the tl;dr crowd) here are the bullet points:
* Yes, the Moon is closer today than usual, but only by less than 2%.
* This does happen around full Moon, which is when we get bigger tides, but that happens every single month. The Moon being closer amplifies that, but only a tiny little bit.
* The Moon’s possible effect on earthquakes has been studied for a long time. The result? Major earthquakes are not correlated with the Moon’s position or distance.
* Anyone claiming this “supermoon” can cause earthquakes or whatnot is, to be blunt, totally, completely, utterly, wrong.
OK, so, how about some details?
I went over a lot of this in my post showing the Moon had nothing to do with the Japanese earthquake. Briefly, the Moon orbits the Earth in an ellipse, so sometimes it’s closer than other times. On average, it’s most distant point (apogee) is about 405,000 km (251,000 miles) and at closest (perigee) it’s about 363,000 km (225,000 miles).
Those numbers change month to month due to the gravity of the Sun and other effects. As it happens, on March 19 at around 02:00 UT (early evening Friday March 18 for most of the US) 19:10 UT [D’oh! Cut and paste accident there, sorry; note this doesn’t affect my argument] the Moon reaches an unusually close perigee distance of a bit more than 357,000 km. Gravitationally, this doesn’t mean much. That extra 6000 km closer than on an average perigee is only about 1.6%, which is pretty trifling. It means the gravity of the Moon on the Earth is only 3% stronger.
The Moon also affects us through tides, which are similar to gravity. But the tides will only be 5% stronger than usual for a perigee due to the Moon’s proximity!
Now to be clear, this is happening at a time of the full Moon (which happens tomorrow, March 19, at 18:10 UT). That means the Sun, Earth, and Moon are roughly lined up in space, so the Sun and Moon’s tidal pulls add together. Every full Moon we get what are called spring tides, with extra high high tides, and extra low low tides. Places prone to flooding do see more on spring tides, every single month of the year. This extra 5% tug this weekend makes that a bit worse, but only a bit.
Earthquakes, volcanoes, panic?
Does this extra tweak have any other effect on the Earth? Could it cause quakes, volcanoes or anything else?
Nope. Again, go read my supermoon post from last week. Earthquakes and the Moon have been studied extensively. Mind you, the Moon orbits the Earth every month, and there are thousands of earthquakes every year, so any correlation between the two would scream out of the data. The best that’s seen is a weak connection between the Moon and shallow, low-magnitude earthquakes. Big earthquakes, like the the ones in Japan, Christchurch, or Chile in the past few months have clearly not been triggered by the Moon. In fact, the Japan quake happened when the Moon was closer to apogee than perigee! That right there is a bit of a showstopper for this “supermoon” idea.
Much more at link. We’ll still be here tomorrow, except for the few who check out from natural causes or get trampled in a local panic.