It's true. The Moon is full on March 19th right about when it's at perigee, its closest to Earth in its monthly orbit. And not all perigees are precisely the same. This one is a trace closer than usual.But not by enough to notice.
There's something that many people (and too much of the news media) never seem to grasp: When it comes to science stories,if you don't know it in numbers, you don't know it at all.
How much bigger is this month's full Moon? Here's the number. It's just 2% bigger than the full Moons of last month and next month. That's one part in fifty. You couldn't tell the difference if you put them side by side.
Big whoop.
There is, however, more to the picture. The difference between the Moon at perigee and apogee, its farthest from Earth each month (just two weeks before and after every perigee), is quite noticeable in a side-by-side comparison, as shown below. But when the Moon is up in the sky and there's no comparison at hand, even that much difference is awfully hard to detect.
The takeaway message from this episode? Astronomy stories inspire people to look up and consider the larger universe, but they can also educate in practical ways for getting through life. The "supermoon" flap is a harmless bit of hype. But when your relatives start sending you frantic chain letters about the Japanese nuclear fallout starting to "pound the West Coast," like one blog post I've already seen going around, remember what you read here:
When it comes to science stories, if you don't know it in numbers, you don't know it at all.
Look at the numbers for the radiation reaching the West Coast. You'll see that it's trivial compared to the natural background radiation that everyone receives every day of their lives.
So don't let anyone tell you that you can't learn anything practical from astronomy. Send your frantic aunt this article, and tell her why she should quit with the dumb chain letters already.
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