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19-year cycle
I have heard every 19 years (235 lunar months) the moon and the solar
year are synchronised. However, after looking at the times for new moons in the almanacs, and comparing new moon times with a year and a year 19 years later, the new moon can be off as much as one day. March 16 in the first year and March 15 in the 20th, which is 19 years later. Why is this? Is there any truth to the 19-year cyle? |
#2
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"David Grossmann" wrote:
I have heard every 19 years (235 lunar months) the moon and the solar year are synchronised. However, after looking at the times for new moons in the almanacs, and comparing new moon times with a year and a year 19 years later, the new moon can be off as much as one day. March 16 in the first year and March 15 in the 20th, which is 19 years later. Why is this? Is there any truth to the 19-year cyle? IIRC it's caused by the fact that the Gregorian calendar isn't precisely synched to sideral time. It does however stay within plus-or-minus a day or two. D. -- Touch-twice life. Eat. Drink. Laugh. -Resolved: To be more temperate in my postings. Oct 5th, 2004 JDL |
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"David Grossmann" kirjoitti glegroups.com... I have heard every 19 years (235 lunar months) the moon and the solar year are synchronised. However, after looking at the times for new moons in the almanacs, and comparing new moon times with a year and a year 19 years later, the new moon can be off as much as one day. The 19-year cycle (known as Meton-cycle after an astronomer in Athens - who probably learned of the concept from Babylonians that had based their calender on it since 383 BC) is real. However: a) It isn't quite accurate - there is a difference of apprximately 2 hours. b) 235 average lunar months is almost exactly 19 years - but not all months are average. The length of synodic month can vary approximately up to 6 hours. Either of these effects or combination thereof could be the source of the difference. You didn't specify the years (or the time zone), so I can not verify that this is the case. A calendar of Moon phases is available at: http://aa.usno.navy.mil/data/docs/MoonPhase.html to the accuracy of minutes. H Tavaila |
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JRS: In article .com
, dated Fri, 11 Feb 2005 08:16:44, seen in news:sci.space.science, David Grossmann posted : I have heard every 19 years (235 lunar months) the moon and the solar year are synchronised. However, after looking at the times for new moons in the almanacs, and comparing new moon times with a year and a year 19 years later, the new moon can be off as much as one day. March 16 in the first year and March 15 in the 20th, which is 19 years later. Why is this? Is there any truth to the 19-year cyle? Were you looking at the times for full moons, or for the dates only? That is the Metonic Cycle, q.v. - Meton and Euctemon of Athens. It is not an exact relationship; and, as far as I know, has never been generally considered to be exact. Using Javascript : 235 * new Date("1970/01/30 12:44:03 GMT") 599589105000 19 * 365.24220 * 864e5 599581595520 Difference 7509480 ms 02:05:09.48 s Ratio 1.0000125245 There are 12.368266145863343 months per year, and that is best approximated by 12:1, 25:2, 37:3, 99:8, 136:11, 235:19, 4131:334, 12628:1021 error 0.37 0.13 0.03 0.007 0.0046 0.00015 0.000027 0.00000026 The Metonic cycle is the shortest one that usually gets the date right. The ratio 99:8 was also anciently known - the octaeteris of Cleostratus of Tenedos. -- © John Stockton, Surrey, UK. Turnpike v4.00 IE 4 © URL:http://www.jibbering.com/faq/ JL/RC: FAQ of news:comp.lang.javascript URL:http://www.merlyn.demon.co.uk/js-index.htm jscr maths, dates, sources. URL:http://www.merlyn.demon.co.uk/ TP/BP/Delphi/jscr/&c, FAQ items, links. |
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JRS: In article , dated Sat, 12
Feb 2005 06:12:43, seen in news:sci.space.science, Derek Lyons posted : "David Grossmann" wrote: I have heard every 19 years (235 lunar months) the moon and the solar year are synchronised. However, after looking at the times for new moons in the almanacs, and comparing new moon times with a year and a year 19 years later, the new moon can be off as much as one day. March 16 in the first year and March 15 in the 20th, which is 19 years later. Why is this? Is there any truth to the 19-year cyle? IIRC it's caused by the fact that the Gregorian calendar isn't precisely synched to sideral time. It does however stay within plus-or-minus a day or two. The Gregorian Calendar year cycle has nothing to do with the Moon, although that rather loosely caused the division into months; nor with Sidereal Time. It is fairly precisely, though irregularly, synched to solar time. That is a further cause of variation of date omitted in my previous article; the error I calculated as being the difference between 235 lunar months and 19 solar years does not include the fluctuation in the length of a Gregorian year, which may be either (about) six hours shorter or eighteen hours longer than the average. As 19 is not evenly divisible by 4, that fluctuation must be added in considering the civil date/time of New Moons. The Metonic period of 19 years must not be confused with the period of the Regression of the Nodes (18.61 years) nor with the Saros (18.03 years, 223 lunations) which is the usual repeat interval for Eclipses. -- © John Stockton, Surrey, UK. Turnpike v4.00 MIME. © Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links; some Astro stuff via astro.htm, gravity0.htm ; quotings.htm, pascal.htm, etc. No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News. |
#6
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Dr John Stockton wrote: JRS: In article .com , dated Fri, 11 Feb 2005 08:16:44, seen in news:sci.space.science, David Grossmann posted : I have heard every 19 years (235 lunar months) the moon and the solar year are synchronised. However, after looking at the times for new moons in the almanacs, and comparing new moon times with a year and a year 19 years later, the new moon can be off as much as one day. March 16 in the first year and March 15 in the 20th, which is 19 years later. Why is this? Is there any truth to the 19-year cyle? Were you looking at the times for full moons, or for the dates only? That is the Metonic Cycle, q.v. - Meton and Euctemon of Athens. It is not an exact relationship; and, as far as I know, has never been generally considered to be exact. Using Javascript : 235 * new Date("1970/01/30 12:44:03 GMT") 599589105000 19 * 365.24220 * 864e5 599581595520 Difference 7509480 ms 02:05:09.48 s Ratio 1.0000125245 There are 12.368266145863343 months per year, and that is best approximated by 12:1, 25:2, 37:3, 99:8, 136:11, 235:19, 4131:334, 12628:1021 error 0.37 0.13 0.03 0.007 0.0046 0.00015 0.000027 0.00000026 The Metonic cycle is the shortest one that usually gets the date right. The ratio 99:8 was also anciently known - the octaeteris of Cleostratus of Tenedos. -- © John Stockton, Surrey, UK. Turnpike v4.00 IE 4 © URL:http://www.jibbering.com/faq/ JL/RC: FAQ of news:comp.lang.javascript URL:http://www.merlyn.demon.co.uk/js-index.htm jscr maths, dates, sources. URL:http://www.merlyn.demon.co.uk/ TP/BP/Delphi/jscr/&c, FAQ items, links. Thanks to everyone who responded. I appreciate your time, Sincerely, David Grossmann |
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