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| The Supermoon will not look like this. Unless you have a telescope. In which case, any full moon could look like this. |
The night sky is set to be illuminated later by what will appear to be a much bigger and brighter Moon, screams the BBC tagline. Well, no, it won't. This is misuse of statistics, but those stats just happen to be hidden beneath weasel terms like 'much bigger' and 'much brighter'.
First of all, we have to ask 'much bigger' and 'much brighter' than what? The obvious comparison is with the night before, and I can confidently predict that the difference will be unnoticeable. But let's go all the way and compare the Moon's appearance this weekend with the way it is at its most distant and dimmest, because of course we can all remember what it looked like months ago. According to the BBC article, it will be 14% brighter than when it is at its furthest away. That sounds a lot, right? Let's compare with light bulbs. The light output of a bulb does not have a linear relationship with the power, but I have calculated that a 66 watt bulb is roughly 14% brighter than a 60 watt bulb. That's the kind of difference we are looking at.
Even more dramatic is the website's claim that the Moon will seem '30% bigger'. Of course this is a meaningless statistic as it doesn't define what is bigger, but let's assume this is the increase in area, as that sound more dramatic than the increase in diameter, and they are bound to use the most dramatic figure to add, erm, a sense of drama to a totally uninteresting event. The apparent diameter of the Moon is about the same as a 5mm punched hole held at arm's length. (Sounds ridiculously small? That's your amazing brain, fooling you.) To produce a 30% increase in area requires a 14% increase in diameter. So assuming my 5mm is the average between Supermoon and Weeniemoon, we are looking at around an apparent diameter of the Moon of the equivalent of about 5.3mm at arm's length at its biggest. Whoopie-doo.
The article compounds confusion by talking about the psychological effect that makes the Moon look much bigger than it really is when it is close to the horizon, trees or buildings as if this is an effect of the Supermoon, rather than something that happens whenever we see the Moon. Groan and double groan.
Altogether an appalling bit of work of which the BBC should be ashamed. They say 'We'd like to see your pictures of the supermoon' as if anyone could tell the difference between them and pictures of any other full moon.
Sadly, even properly scientific sources are going a bit bonkers over this, trying to get their moment in the spotlight (or Supermoonlight). Stop being naughty, people. It's a small effect of very little significance. Tell us some real science.
Image from Wikipedia
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