Full Moon on Friday the 13th
Alan French
this happens, or, perhaps, what the odds are? I assume this is not a simple
probability question (1 day in 7 is Friday, 1 day in about 30 is the
13th,...) as it does not involve random events.
Clear skies, Alan
Doug S.
As it happens, a member of our club just calculated this. Full moons on Friday
the 13th occur every 15 years or so. The next one will be in June 2014. Someone
also asked us when the next OCTOBER 13th full moon would occur. That will be in
2073.
A long wait!
Doug S.
do...@frostydrew.org
Ernie Wright
Here's a 200-year span.
Mar 1903
Oct 1905
Jun 1919
Jan 1922
Nov 1970
Jul 1984
Feb 1987
Mar 1998
Oct 2000
Jun 2014
Aug 2049
Apr 2063
Nov 2065
Feb 2082
Oct 2084
Mar 2093
Jun 2098
May 2101
About every 11 years on average, judging by this, but the intervals
aren't at all regular, e.g. January 1922 to November 1970.
- Ernie http://members.home.net/erniew
Sam Wormley
>
> This coming Friday the 13th is also a Full Moon. Does anyone know how often
> this happens, or, perhaps, what the odds are? I assume this is not a simple
> probability question (1 day in 7 is Friday, 1 day in about 30 is the
> 13th,...) as it does not involve random events.
>
The probabilities are similar to New Moons occuring of Saturday the 12ths
and First quarters occuring on Wednesday the 11ths. And so on. There is
nothing unique about Friday the 13th in nature.
________________________________________________________________________
Sam Wormley - http://www.cnde.iastate.edu/staff/swormley/eo/science.html
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Michael A. Covington
"Alan French" <Sue_and_A...@email.msn.com> wrote in message
news:8s0gr...@news1.newsguy.com...
> This coming Friday the 13th is also a Full Moon. Does anyone know how
often
> this happens, or, perhaps, what the odds are? I assume this is not a
simple
> probability question (1 day in 7 is Friday, 1 day in about 30 is the
> 13th,...) as it does not involve random events.
No, but since the lunar month is a fixed length, and the calendar is not
synchronized with it, it's as good as random, I'd think.
brow...@prairienet.org
Mathmatically, I get 1 every 16.33 years on the average. That assumes 1
full moon every 28 days, 1 friday every 7 days and 12 13ths every year
(28*7/12). As others have correctly pointed out, they can be VERY
irregularly spaced.
Bryan
Alan French <Sue_and_A...@email.msn.com> wrote:
: This coming Friday the 13th is also a Full Moon. Does anyone know how often
: this happens, or, perhaps, what the odds are? I assume this is not a simple
: probability question (1 day in 7 is Friday, 1 day in about 30 is the
: 13th,...) as it does not involve random events.
: Clear skies, Alan
Hilton Evans
Don't tell Wall Street <g>
--
Hilton Evans
-----------------------------------------------
ChemPen Chemical Structure Software
http://home.ici.net/~hfevans/chempen.htm
Alan French
Although it may seem true that there is nothing special about a Full Moon on
Friday the 13th, there is something special about Friday falling on the
13th. According to Ottewell "Actually, Friday falls on the 13th more often
than any other day does! In every span of 400 years after 1582 (the
beginning of the Gregorian calendar) the numbers of Sundays-the-13th,
Mondays-the-13th etc. are: 687, 685, 685, 687, 688, 684."
Clear skies, Alan
"Sam Wormley" <swor...@cnde.iastate.edu> wrote in message
news:39E459D8...@cnde.iastate.edu...
> Alan French wrote:
> >
> > This coming Friday the 13th is also a Full Moon. Does anyone know how
often
> > this happens, or, perhaps, what the odds are? I assume this is not a
simple
> > probability question (1 day in 7 is Friday, 1 day in about 30 is the
> > 13th,...) as it does not involve random events.
> >
> > Clear skies, Alan
>
Alan French
At least for recent spans of times though, it comes out higher than simple
probability would predict.
Clear skies, Alan
"Michael A. Covington" <See http://www.CovingtonInnovations.com for address>
wrote in message news:8s1ssp$ls6$1...@slb1.atl.mindspring.net...
>
> "Alan French" <Sue_and_A...@email.msn.com> wrote in message
> news:8s0gr...@news1.newsguy.com...
> > This coming Friday the 13th is also a Full Moon. Does anyone know how
> often
> > this happens, or, perhaps, what the odds are? I assume this is not a
> simple
> > probability question (1 day in 7 is Friday, 1 day in about 30 is the
> > 13th,...) as it does not involve random events.
>
Alan French
My wife checked from 1970 to 2050 and found the 7 you listed in the 81
years.
According to Ottewell, "In every span of 400 years, after 1582, there are
688 Friday the 13ths."
Thanks everyone!
Clear skies, Alan
"Ernie Wright" <ern...@home.com> wrote in message
news:39E3F887...@home.com...
Sam Wormley
>
> Sam,
>
> Although it may seem true that there is nothing special about a Full Moon on
> Friday the 13th, there is something special about Friday falling on the
> 13th. According to Ottewell "Actually, Friday falls on the 13th more often
> than any other day does! In every span of 400 years after 1582 (the
> beginning of the Gregorian calendar) the numbers of Sundays-the-13th,
> Mondays-the-13th etc. are: 687, 685, 685, 687, 688, 684."
>
> Clear skies, Alan
>
Thanks Alan--Ottewell is an excellent source for interesting data such as
Friday the 13th. My posting was meant to dispel the fact that Friday the
13th, although popular in Western culture, has no real statistical significance,
any more than any other day/date combination. For a good layman level background
in numerical issues, I highly recommend that folks read John Allen Paulos' books
such as:
"A Mathematician Reads The Newspaper"
"Innumeracy"
"Beyond Innumeracy"
Alan French
Sue expanded your results. Here are more dates that, when added to yours,
give a 400 year sample - from 1701 to 2100. (She agrees with all the dates
you found too.) Taking just the 400 years (no May 2101) - since there may
be a 400 year cycle (Ottewell) - you get a total of 32 dates in 400 years,
or, on average, one every 12.5 years. Adding the one year and one date
gives 33 dates in 401 years, or one every 12.15 years.
Clear skies, Alan
Sep 1715
May 1729
Nov 1750
Oct 1761
Jul 1764
Feb 1767
Mar 1778
Oct 1780
Jun 1794
Jan 1797
Feb 1835
Oct 1837
Mar 1846
Jun 1851
May 1881
........
"Ernie Wright" <ern...@home.com> wrote in message
news:39E3F887...@home.com...
Ric Werme
>Alan French wrote:
>>
>> This coming Friday the 13th is also a Full Moon. Does anyone know how often
>> this happens, or, perhaps, what the odds are? I assume this is not a simple
>> probability question (1 day in 7 is Friday, 1 day in about 30 is the
>> 13th,...) as it does not involve random events.
>>
>> Clear skies, Alan
>The probabilities are similar to New Moons occuring of Saturday the 12ths
What's special about Saturday the 12ths, other than they never occur in
months that have Friday the 13ths?
One thing that's special about October Friday 13ths is that I was born
on one and will start my 50th loop around the Sun on Friday. That's old
enough to make it worthwhile to adjust the start time for the precession
of the equinoxes.
--
Ric Werme | we...@nospam.mediaone.net
http://people.ne.mediaone.net/werme | ^^^^^^^ delete
Ernie Wright
> Sue expanded your results. Here are more dates that, when added to
> yours, give a 400 year sample - from 1701 to 2100. (She agrees with
> all the dates you found too.)
I'm glad we're getting the same answers. Otherwise I'm not sure where
I'd go to independently verify them!
For what it's worth, I looked ahead another 800 years and only found 45
additional dates, for a total of 78 between 1701 and 2900. This would
bring the frequency up to about 1 in 15.6 years.
- Ernie http://members.home.net/erniew
Alan French
I got 32 dates from Jan 1701 to Dec 2000. Your original list had 1 in
2001, which I didn't count since I stopped at an even 400 years. Did you
get 45 more from Jan 2001 or Jan 2002? In the first case we'd 77 in 1200
and the 1 in 15.6 you calculated. In the second case we'd have the 78 in
1200 total you gave, but that would be 1 in 15.4.
Clear skies, Sue
"Ernie Wright" <ern...@home.com> wrote in message
news:39E56B2...@home.com...
Alan French
That sould have said:
I got 32 dates from Jan 1701 to Dec 2100. Your original list had 1 in
2101, which I didn't count since I stopped at an even 400 years. Did you
get 45 more from Jan 2101 or Jan 2102? In the first case we'd 77 in 1200
and the 1 in 15.6 you calculated. In the second case we'd have the 78 in
1200 total you gave, but that would be 1 in 15.4.
Not that one more day makes much difference.
Clear skies, Sue
"Alan French" <Sue_and_A...@email.msn.com> wrote in message news:...
Ernie Wright
> I got 32 dates from Jan 1701 to Dec 2000. Your original list had 1
> in 2001, which I didn't count since I stopped at an even 400 years.
> Did you get 45 more from Jan 2001 or Jan 2002? In the first case we'd
> 77 in 1200 and the 1 in 15.6 you calculated. In the second case we'd
> have the 78 in 1200 total you gave, but that would be 1 in 15.4.
You're right, I got 1/15.6 based on a total of 77. I remembered the May
2001 occurrence, bringing the total to 78, but I forgot to correct the
frequency.
To be more precise about what I did, I found the 12500 full Moons after
1 January 1900 and tested each of them to see whether they fell on a
Friday the 13th. The actual end date for the interval I tested was the
date of the 12500th full Moon, 12 August 2910, and the last Friday the
13th full Moon I found was in July 2891. I found a total of 63 events
between Jan 1900 and Aug 2910.
The full Moon finding routine is based on Elwood Downey's in his old
EPHEM program, a C version of a BASIC program by Duffett-Smith based on
the algorithm by Meeus in ASTRONOMICAL FORMULAE FOR CALCULATORS. It's
quite fast, so I could easily search much longer intervals, but I don't
know how much its accuracy erodes at far times. (Meeus may estimate
this, but I don't happen to have his book. Duffett-Smith doesn't say.)
The Gregorian calendar repeats every 400 years (146097 days, 20871
weeks), but assuming for a moment that the Meeus algorithm is adequate,
I don't find any repeat in the full Moon pattern over a period of 16000
years, at least not when defined in the following way,
remainder of ( jd2 - jd1 ) / 146097.0 less than .04
which would be two full Moons on the same day of the month separated by
an exact multiple of 400 years, to within an hour. I would expect the
full Moon + calendar cycle to be a multiple of 400 years long, but maybe
I'm wrong about that, or the Meeus formula just can't see that far.
- Ernie http://members.home.net/erniew
SkySea
that was mentioned in one of the first posts in this thread (by Doug S.?).
Does Oct 13, 2073 have a Full Moon, or no?
- Dale Gombert ( SkySea at AOL . COM )
122.38W, 47.58N, W. Seattle, WA
Ernie Wright
> In the expanded lists, I don't see any mention of the Oct 13, 2073
> occurance that was mentioned in one of the first posts in this thread
> (by Doug S.?).
>
> Does Oct 13, 2073 have a Full Moon, or no?
No. The full Moon in October 2073 occurs on the 16th. The next Friday
the October 13th full Moon will be in 2084.
- Ernie http://members.home.net/erniew
Alan French
Here is a good URL with Moon phases...
http://sunearth.gsfc.nasa.gov/eclipse/phase/phasecat.html
Clear skies, Alan
"SkySea" <sky...@aol.com.wa.us> wrote in message
news:20001013010943...@ng-ch1.aol.com...
Alan French
I'm impressed. I used the 5000 year moon phase tables at
http://sunearth.gsfc.nasa.gov/eclipse/phase/phasecat.html
I just scanned the Full Moon column for 13s, then checked the calendar on my
cheap little planetarium software (Expert Astronomer) to see if the dates
were Fridays.
Clear skies, Sue
"Ernie Wright" <ern...@home.com> wrote in message
news:39E3F887...@home.com...
Linds
"Alan French" <Sue_and_A...@email.msn.com> wrote:
> This coming Friday the 13th is also a Full Moon. Does anyone know how
often
> this happens, or, perhaps, what the odds are? I assume this is not a
simple
> probability question (1 day in 7 is Friday, 1 day in about 30 is the
> 13th,...) as it does not involve random events.
>
>
> Sounds interesting.
Sent via Deja.com http://www.deja.com/
Before you buy.
to...@spamfree.nowhere.nu
> Ernie,
> That sould have said:
> I got 32 dates from Jan 1701 to Dec 2100. Your original list had 1 in
> 2101, which I didn't count since I stopped at an even 400 years. Did you
> get 45 more from Jan 2101 or Jan 2102? In the first case we'd 77 in 1200
> and the 1 in 15.6 you calculated. In the second case we'd have the 78 in
> 1200 total you gave, but that would be 1 in 15.4.
> Not that one more day makes much difference.
Ok, to push it even further. How often does a total lunar eclipse occur
on Friday the 13th?
tony
--
Tony
This is a free country; and I have the permits, licenses, stamps,
tags, stickers, background checks, and tax receipts to prove it.
Ernie Wright
> Ok, to push it even further. How often does a total lunar eclipse
> occur on Friday the 13th?
In the 4000 years between Jan 0001 and Dec 4000, there are 250 Friday
the 13th full Moons, and total lunar eclipses occur on 16 of those.
May 477
Feb 705
Dec 726
Dec 1247
Oct 1837
Nov 2589
Aug 2641
Mar 2742
Aug 3013
May 3092
Mar 3114
Apr 3494
Feb 3665
Dec 3686
Jul 3787
Mar 3896
- Ernie http://members.home.net/erniew
Ernie Wright
> I used the 5000 year moon phase tables at
> http://sunearth.gsfc.nasa.gov/eclipse/phase/phasecat.html
>
> I just scanned the Full Moon column for 13s, then checked the calendar
> on my cheap little planetarium software (Expert Astronomer) to see if
> the dates were Fridays.
Excellent link. And this probably didn't take any longer than it took
me to write my program.
- Ernie http://members.home.net/erniew
Nick Taylor
Thanks! Keep in mind that the moon phase tables at:
http://sunearth.gsfc.nasa.gov/eclipse/phase/phasecat.html
are UT (GMT) dates, so if the time falls between midnight and 0300 those
of us in the U.S. will have the full moon on Thursday the 12th. And, if
the Greenwich time is just before midnight those in Eastern Europe will
have their full moon on Saturday the 14th.
Have fun,
-Nick
to...@spamfree.nowhere.nu
>> Ok, to push it even further. How often does a total lunar eclipse
>> occur on Friday the 13th?
> In the 4000 years between Jan 0001 and Dec 4000, there are 250 Friday
> the 13th full Moons, and total lunar eclipses occur on 16 of those.
> May 477
> Feb 705
> Dec 726
> Dec 1247
> Oct 1837
> Nov 2589
I'd love to say I'll be around for the next one...but I won't hold my
breath. :)
tony