please empty your brain below
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Oh good. I thought the press coverage of this phenomenon was particularly useless. But "supermoon" (gosh! super! wow!) is good marketing.
Two points. First, Rayleigh scattering - the same effect that causes the sky to be blue, and sunsets and sunrises to be orange or red - means that the filtered sunlight incident on the Moon during a total lunar eclipse already has a reddish hue. It is not the reflection by the Moon that causes a change in the colour.
Secondly, the albedo of the Moon is about 0.12. So most of the light is not reflected back. It is actually a pretty dark grey.
Andrew | 31.01.18 - 7:46 a.m. | #
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Sorry, third point: how can New Zealand ever get a blue moon in February, when the month still has only has 28 days (or 29 in a leap year)?
dg writes: I didn't say it did.
Andrew | 31.01.18 - 7:51 a.m. | #
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Great write up - good subject and one of your pet hates “click bait”. One question though, why is the word blue used in this context of rarity?
Richard | 31.01.18 - 7:52 a.m. | #
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And I meant to plug Phil Plait, who is pretty good on this sort of thing. He compares the supermoon hyperbole to a superman who is 10% stronger than an average person. Not so super, eh. http://www.syfy.com/syfywire/dont-it-make-my-red-moon-blue-how-to-watch-the-total-lunar-eclipse-on-january-31
Andrew | 31.01.18 - 7:53 a.m. | #
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As far as I am aware, the origin of the term "blue moon" is not know with any certainty. There are some ideas. But someone else may be able to give chapter and verse.
Andrew | 31.01.18 - 7:54 a.m. | #
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The frequency you cite for a blue moon (7 times in 19 years) is interesting. It is the same frequency that the Jewish Rabbis about 2000 years ago determined for adding a "leap month" to the Jewish year in order to maintain the Festival of Passover in the spring.
Dave | 31.01.18 - 7:58 a.m. | #
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I'm in a part of the world at the moment where we'll get a great view of the eclipse, at a fairly reasonable 10.30pm. Except it'll be cloudy tonight.
martin | 31.01.18 - 8:07 a.m. | #
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No doubt the 'super moon' will be mentioned in the weather forecast, and added as a tail item on the news, TfL can put up notices on surface stations, warning about being distracted. Another way for the moon to appear larger is to look at it through binoculars or a telescope, if that's too much effort, you can find an image on the internet and enlarge it.
Still Anon | 31.01.18 - 8:10 a.m. | #
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I hope you'll remind us again when the more worthwhile/visible manifestations are imminent.
Sarah | Homepage | 31.01.18 - 8:20 a.m. | #
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Dave: it is the 19 year Metonic cycle, named after a Greek but known the the Babylonians. You need 7 intercalary months every 19 years to keep the lunar months (about 29.53 days) in synch with the solar year (about 365.242 days).
Now I have said quite enough and shall shut up for a bit.
Andrew | 31.01.18 - 8:21 a.m. | #
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Andrew is the new Timbo.
louise | 31.01.18 - 8:27 a.m. | #
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Surely, if there is anything to be seen it is the height of the tides today?
dg writes: Only a couple of inches higher than the usual spring tides.
b | 31.01.18 - 9:26 a.m. | #
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"when the moon is within 90% of its closest approach to Earth "
I don't understand that bit - surely 90% of a minimum value is an even smaller number, and therefore is never attained. (90% of 356,566km is about 321,000km).
dg writes: Richard's definition is notoriously vague, and people interpret it in a variety of ways.
timbo | 31.01.18 - 10:02 a.m. | #
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In fact the time difference with New Zealand is 13 hours at present, as they are in daylight savings and we are not. So 1326 on Wednesday UK time will be 0226 on Thursday. So, yes, definitely no blue moon for them.
Gordon | 31.01.18 - 11:44 a.m. | #
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12.52 to 2.08 ... adding 8 would give 8.52 to 10.08 ... heck it's just over half an hour away! Pity that my apartment faces west and I will be having dinner, and most importantly it's too cold and cloudy that I have little reason to go out!
Patrickov | 31.01.18 - 12:17 p.m. | #
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@Dave @Andrew : The traditional Chinese calendar do the same as well. Thst's why our new year keeps jumping between late Jan and mid Feb.
Patrickov | 31.01.18 - 12:20 p.m. | #
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Such an education! I enjoyed reading this post whilst comparing to real life visuals.
louise | 31.01.18 - 6:34 p.m. | #
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This super moon stuff aways drives me potty. I made it my photo of the day today:
[my photo of the day]
(with a link back to here of course)
Andy Norman | Homepage | 31.01.18 - 7:01 p.m. | #
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You mention NZ and some Pacific Islands, but I want to point out most of east coast Australia, where the Bureau of Meteorology helpfully tweeted that we didn't technically have a blue moon, because of daylight saving.
Jonathan D | 31.01.18 - 10:32 p.m. | #
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[Sorry, must have misread what you wrote about New Zealand]
Full(ish) Moon still looking great this morning, as it was last evening. Much as it does every lunar month.
Andrew | 01.02.18 - 7:02 a.m. | #
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Well done for cutting through the ahem lunacy of the supermoon hype. I'm not sure though that the 'super blue blood moon' of December 1982 had the 'blood' bit - the lunar eclipse wasn't visible from London according to NASA:
https://eclipse.gsfc.nasa.gov/LEplot/LEplot1951/LE1982Dec30T.pdf
dg writes: Agreed, and updated, thanks.
GJ | 01.02.18 - 8:16 a.m. | #
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But the 1982 event was a "super" moon, and a "blue" moon in some places, and a "blood" moon (lunar eclipse) in some places too. Was there any place (not in London) where it would have been all three - the so-called "cosmic trifecta"?
dg writes: Yes. Iceland.
Or was it really a once-in-150 years event?
Andrew | 01.02.18 - 12:31 p.m. | #
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