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| Debunking the ‘Supermoon’ The tide is high! By Garry Nicholson | |
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| Tweet Topic Started: 9 Aug 2014, 06:46 PM (71 Views) | |
| Audi-Tek | 9 Aug 2014, 06:46 PM Post #1 |
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Debunking the ‘Supermoon’ The tide is high! By Garry Nicholson As expected, there are the usual scare stories doing the rounds in the sensationalist media about this weekend’s so-called ‘Super-Moon’, so let’s put a few facts in place amidst all the ‘Apocalypse-now’ excitement… So what is this ‘super-moon’? I really don’t like that phrase, because it implies something really unusual, and I think it was only coined in recent years in astrological circles. That’s astrology, not astronomy, and I assume the good readers of weatherweb.net know the difference! This Sunday, 10th August, is Full Moon, occurring precisely at 18:11 UTC. This closely coincides with the Perigee of the Moon - the closest point in the monthly elliptical lunar orbit – at 17:44 UTC on Sunday. In terms of time, this is the closest combination of Full Moon and Perigee this year. The Moon will be approximately 356,900km (221,700 miles) from Earth at this time. Because the phases of the Moon, and the distance of the Moon are two separate cycles, this means such a coincidence of the two varies over time. We had a similar situation on July 12th and 13th, where Full Moon and Perigee occurred 21 hours apart, and the Moon was 358,250km from Earth. We will have another on September 8th and 9th, where the difference is 22 hours, at roughly 358,400km from Earth. By October 8th, the difference is 2 days, with Perigee occurring on October 6th, at 362,500km. It takes around 13 months to return to the closest matching point of Full Moon and Perigee. In the mean-time, around 6 to 7 months after Full Moon and Perigee, there will be New Moon at Perigee, although this causes less excitement because we can’t see it. Last winter, we had a New Moon at Perigee on New Year’s Day, 356,900km from Earth. This month, the next New Moon, on 24th August, will occur at the opposite side of the lunar elliptical orbit – Apogee – and will be 406,500km from Earth. A Full Moon at Perigee is around 12-13% larger than at Apogee, and around 30% brighter, but the difference can be very difficult to spot unless you are very observant. Bear in mind, that the Moon always appears much bigger when close to the horizon, due to an optical illusion. Pictures of a ‘giant moon’ in the newspapers will be using a very close up and tricked up image! Plus or minus a few tens of kilometres, each Full Moon at Perigee will be more or less the same distance from the Earth. Of course, if taken precisely, there will be some ‘record’ closeness at some point, but any indication that this is the ‘closest for 20 years’ or something like that should really be taken with a pinch of salt given the distances involved. Perigee occurs every 27 to 28 days, and Apogee is around 14 days after Perigee. When Perigee occurs at the point of New or Full Moon, the gravitational manoeuvrings of the Earth and Moon system mean that Perigee is closer to Earth than at other Perigees. For example a Perigee half-moon in April was around 369,700km from Earth. At times of Full (or New) Moon and Perigee the ‘astronomical’ fortnightly spring tides are enhanced, meaning high tide is a little higher than usual, and low tide is a little lower. I did a musing about this earlier in the summer, highlighting the risk of low tides, but mentioning the risk of high tides too. As it turns out, this weekend and next week will have greater concerns about high tides, given the wind and low pressure affecting the UK. A similar situation was the cause of the big seas seen in last winter’s storms, although obviously with fiercer storm systems. If you have been a regular visitor to my musings over the past year or so, you may have read my ‘Moon thoughts’ before. In short, I am researching the combination of high tides and storms, among other things, to look at the influence of such lunar cycles as a potential external forcing mechanism on weather patterns, as a small ‘cog’ in the very big wheel that is the atmospheric system. I would not say that Bertha, or the low pressure currently affecting the UK, can be directly attributed to this current lunar situation, but it remains part of my research none-the-less. Nor would I ever seek to ‘doom-monger’ about the “Super-Moon” – that can be left to the quacks and tabloids! Source .................... http://www.weatherweb.net/ |
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9:56 AM Jul 11