This amazing shot was taken by astronaut André Kuipers from the International Space Station on May 5, 2012, as the perigee full Moon set behind the Earth’s limb. The Earth’s atmosphere bends light from the Moon, acting like a lens, pushing the bottom part of the Moon up into the top.
Science once again saves me from embarrassment. I was pretty sure the Moon wouldn’t take it personally.
Image credit: ESA/NASA
So, tonight is the so-called Supermoon, when the Moon happens to be full at the same time it’s at perigee, the point in its orbit closest to the Earth. This makes it somewhat larger and brighter than normal, and that’s getting a lot of attention in the press. I pointed out a few days ago that in reality, you almost certainly won’t notice the difference between this full Moon and any other, mostly because the difference is small, and our eyes and brain are terrible at judging things like that without something to directly compare it to.
I was thinking about this last night as I watched the almost-full Moon rise in the east (which, I’ll add, ironically looked huge due to the Moon Illusion!), and thought of something that might help illustrate this last point.
Imagine you go outside tonight to look at the full Supermoon rising in the east. Imagine also you’re holding a US dime in your hand (if you live in another country, feel free to substitute your local currency, but beware of the math; hang on a minute to see).
Let me ask you this: How far away would you have to hold the dime so that it appears as big as the Moon to you?
A few inches? A foot? (Convert to metric if you wish). Go ahead, guess!
… OK, ready? [Answer is below the fold so as not to spoil it.]
Well, yeah. Still, funny.
And man. Those two women must really be tired of me. First the Moon Illusion in the park, and now this.
You may’ve seen some folks writing about this weekend’s so-called Supermoon. I suppose I’m not surprised, but it’s still irritating. Why? Because it’s just hype (and to get this out of the way immediately, will have no real effect on the Earth, either). Here’s the scoop.
This weekend, on the night of May 5/6, the Moon will be full. This happens every 29 days or so when the Moon is opposite the Sun in the sky, and we see its face fully illuminated.
As it happens, the Moon’s orbit is elliptical, and so sometimes the Moon is a bit closer to the Earth than other times. Every now and again the Moon is full when it’s also closest to Earth — the point in its orbit called perigee. May 5th is one of those times.
What does this mean? Well, it means the Moon is closer, so it will appear a bit bigger and brighter than usual. But here’s the thing: you’d never know. Seriously, to the eye it’ll look exactly the same as it always does when it’s full. The Moon is actually pretty small in the sky — if you don’t believe me, go outside tonight, find the Moon, and hold your thumb up at arm’s length next to it; it’ll easily cover the Moon entirely (my thumb is 2 – 3 times wider than the Moon). A small change in its size is something that’s really hard to see.
To be specific, according to Fourmilab, the Moon will be 356,953 kilometers from Earth when it’s full. However, last month, on April 7, when it was full it was about 358,313 km away. That’s a difference of 1400 km, less than 1%. So really, the size of the full Moon this weekend won’t be any different than it was last month, and no one was writing about it then. And to show I’m not being biased, take a look at when the Moon was full near apogee — the most distant point in its orbit. That’ll happen in late November of 2012, when it’ll be at a distance of 406,364 km. That’s still only a difference of less than 14%.
That’s a pretty small change, not enough to notice by eye. Read More
Every now and again I chat with astronomer Seth Shostak about some astronomical skullduggery as part of the SETI radio show "Are We Alone". The segment is called Skeptic Check, and the latest is now online, where Seth and I apply a little kryptonite to the idea of the "supermoon" causing earthquakes.
You can also hear Joe Nickell talking Bigfoot, and other scientists discussing the Mozart Effect and magic. It’s a good show… but as we say, don’t take our word on it. Go hear it for yourself!
[NOTE (added March 19): It occurs to me that some people might see the Moon rising today and think it looks HUGE because it’s a "supermoon". However, it’s far more likely they’re falling victim to the famous Moon Illusion. You can read all about it here.]
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:
OK, so, how about some details?
[UPDATE: I have posted an article with more info on the earthquake and where you can donate money toward the relief efforts.]
Japan suffered a massive earthquake last night, measuring nearly magnitude 9. This is one of the largest quakes in its history, causing widespread and severe damage. Before I say anything else, I’m greatly saddened by the loss of life in Japan, and I’ll be donating to disaster relief organizations to help them get in there and do what they can to give aid to those in need.
While there isn’t much I can do to directly help the situation in Japan, I do hope I can help mitigate the panic and worry that can happen due to people blaming this earthquake on the so-called "supermoon" — a date when the Moon is especially close to the Earth at the same time it’s full. So let me be extremely clear:
Despite what a lot of people are saying, there is no way this earthquake was caused by the Moon.
The idea of the Moon affecting us on Earth isn’t total nonsense, but it cannot be behind this earthquake, and almost certainly won’t have any actual, measurable effect on us on March 19, when the full Moon is at its closest.
So, how can I be so sure?
The gravity of the situation
Here’s the deal. The Moon orbits the Earth in an ellipse, so sometimes it’s closer to us and sometimes farther away. At perigee (closest point) it can be as close as 354,000 km (220,000 miles). At apogee, it can be as far as 410,000 km (254,000 miles). Since the Moon orbits the Earth every month or so, it goes between these two extremes every two weeks. So if, say, it’s at apogee on the first of the month, it’ll be at perigee in the middle of the month, two weeks later.
The strength of gravity depends on distance, so the gravitational effects of the Moon on the Earth are strongest at perigee.
However, the Moon is nowhere near perigee right now!
The Moon was at apogee on March 6, and will be at perigee on March 19. When the earthquake in Japan hit last night, the Moon was about 400,000 km (240,000 miles) away. So not only was it not at its closest point, it was actually farther away than it usually is on average.
So again, this earthquake in Japan had nothing to do with the Moon.
Time and tide
So why would people think this is due to the Moon?