Article-I.D.: mordor.2803
Posted: Thu Jul 25 10:44:42 1985
Date-Received: Sat, 27-Jul-85 01:19:03 EDT
Sender: daemon@mordor.UUCP
Organization: S-1 Project, LLNL
Lines: 13

From: Houser@MIT-MULTICS.ARPA


          A book I was reading recently mentioned  that  over  time  the
angle  of  the plane of the ecliptic changes.  The consequence is that
the latitude of the tropics also move.  While this  makes  sense,  the
book  also  stated that there is no formula which describes the motion
over  time.  Is  this  really  true?  The  context  was  that  certain
archeological  sites  are  solstice  oriented  and could be accurately
dated if it was known in what year a Tropic was at  X  latitude.  Just
curious.

                                        jim@tycho

Article-I.D.: lsuc.738
Posted: Mon Jul 29 19:58:30 1985
Date-Received: Mon, 29-Jul-85 21:23:10 EDT
References: <2803@mordor.UUCP>
Reply-To: msb@lsuc.UUCP (Mark Brader)
Organization: Law Society of Upper Canada, Toronto
Lines: 19
Xref: utcs net.space:3814 net.astro:832
Summary: Reposted from net.space as cross-posting to net.astro

This item entered net.space from the Arpa side.  On Usenet it obviously
belongs in net.astro.  I'm reposting it as a cross-posting so that followups
will go both to Usenet net.astro types and to the Arpans who originated it.

Reposted by Mark Brader

> From: Houser@MIT-MULTICS.ARPA
> 
> 
>           A book I was reading recently mentioned  that  over  time  the
> angle  of  the plane of the ecliptic changes.  The consequence is that
> the latitude of the tropics also move.  While this  makes  sense,  the
> book  also  stated that there is no formula which describes the motion
> over  time.  Is  this  really  true?  The  context  was  that  certain
> archeological  sites  are  solstice  oriented  and could be accurately
> dated if it was known in what year a Tropic was at  X  latitude.  Just
> curious.
> 
>                                         jim@tycho

Article-I.D.: phoenix.1250
Posted: Mon Jul 29 09:37:43 1985
Date-Received: Wed, 31-Jul-85 02:16:42 EDT
References: <2803@mordor.UUCP>
Organization: AT&T Information Systems, Lincroft NJ
Lines: 35

>A book I was reading recently mentioned  that  over  time  the
>angle  of  the plane of the ecliptic changes.  The consequence is that
>the latitude of the tropics also move.  While this  makes  sense,  the
>book  also  stated that there is no formula which describes the motion
>over  time.  Is  this  really  true?  The  context  was  that  certain
>archeological  sites  are  solstice  oriented  and could be accurately
>dated if it was known in what year a Tropic was at  X  latitude.  Just
>curious.

As far as I know, this process is known as "nutation".
The earth's axis of rotation precesses around a point in
space with a period of 20,000 years or so.  Superimposed on this
motion is another motion with a much shorter period.
I think nutation is caused by sun-moon gravitational effects on
the earth's equatorial bulge and tidal friction.

The effect over time is that the season's slowly shift around the
year, so that in 11,000 years time you'll be eating lettuce salads
for Christmas dinner like New Zealanders do!

As far as I know - nutation IS predictable.  There is even a clock
somewhere with extra dials for years, centuries etc.  The slowest
movement is the nutation dial.
Interestingly, the earth is not fixed to it's axis of rotation.
The north & south poles can move tens of yards every year.
I've seen a map showing the south pole moving erratically
(drunken walk) within a radius of 100 yards or so.
I don't think this movement is predictable.  I guess they
have the barber pole on wheels . :-)
-- 
				
Made in New Zealand -->		Brent Callaghan
				AT&T Information Systems, Lincroft, NJ
				{ihnp4|mtuxo|pegasus}!phoenix!brent
				(201) 576-3475

Article-I.D.: mordor.2849
Posted: Mon Jul 29 16:09:38 1985
Date-Received: Wed, 31-Jul-85 22:43:16 EDT
Sender: daemon@mordor.UUCP
Organization: S-1 Project, LLNL
Lines: 37

From: mcgeer%ucbkim@Berkeley (Rick McGeer (on an aaa-60-s))

>
>          A book I was reading recently mentioned  that  over  time  the
>angle  of  the plane of the ecliptic changes.  The consequence is that
>the latitude of the tropics also move.  While this  makes  sense,  the
>book  also  stated that there is no formula which describes the motion
>over  time.  Is  this  really  true?  The  context  was  that  certain
>archeological  sites  are  solstice  oriented  and could be accurately
>dated if it was known in what year a Tropic was at  X  latitude.  Just
>curious.
>
>                                        jim@tycho
>


	Wrongo.  The phenomenon you're referring to is called the
"precession of the equinox" and the values have been calculated *very*
precisely.  Roger Bacon first pointed out the phenomenon is the 13th
Century, and showed that if the Julian calendar were not changed, then
sometime in the 30th Century Easter would occur in midsummer (the rate of
precession is about .75 days/century).  The solution he proposed was the one
adopted in the Gregorian calendar, in which Leap Years are not held in
century years and are held every 400th year: so there was no leap year in
1900, there will be one in 2000, but there won't be one in any of 2100,
2200, 2300.

	Incidentally, the world shifted to the Gregorian calendar at varying
times.  The Roman Catholic world did it first, in the 16th Century -- but
that was after the Schism, and so England didn't follow suit.  For 200 years
England's calendar trailed the European by first 9, then 10, then 11 days.
England finally converted in the mid-18th Century, to riots (11 days were
dropped from the calendar at the stroke of a pen).  Russia converted after
the Bolshevik revolution; this is why the "October revolution" was really
held, by Western calendars, in November.

						Rick.

Article-I.D.: mordor.2921
Posted: Fri Aug  2 13:22:31 1985
Date-Received: Sun, 4-Aug-85 05:48:19 EDT
Sender: daemon@mordor.UUCP
Lines: 13

From: jrv@Mitre-Bedford

>         Incidentally, the world shifted to the Gregorian calendar at varying
> times.  The Roman Catholic world did it first, in the 16th Century -- but
> that was after the Schism, and so England didn't follow suit.  For 200 years
> England's calendar trailed the European by first 9, then 10, then 11 days.
> England finally converted in the mid-18th Century, to riots (11 days were
> dropped from the calendar at the stroke of a pen)...

I believe the reason for the riots was that people were forced to pay a whole
month's rent for the short month.

				       - Jim Van Zandt

Article-I.D.: mordor.2924
Posted: Fri Aug  2 15:41:30 1985
Date-Received: Sun, 4-Aug-85 05:49:15 EDT
Sender: daemon@mordor.UUCP
Lines: 26

From: mcgeer%ucbkim@Berkeley (Rick McGeer (on an aaa-60-s))


>>        Incidentally, the world shifted to the Gregorian calendar at varying
>> times.  The Roman Catholic world did it first, in the 16th Century -- but
>> that was after the Schism, and so England didn't follow suit. For 200 years
>> England's calendar trailed the European by first 9, then 10, then 11 days.
>> England finally converted in the mid-18th Century, to riots (11 days were
>> dropped from the calendar at the stroke of a pen)...
>
>I believe the reason for the riots was that people were forced to pay a whole
>month's rent for the short month.



	Rents in those days were charged by the quarter.  Anyway, you're
right, but that was, sad to say, secondary.  People were really upset
because they'd been made 11 days older at the stroke of a pen..."Give us
back our 11 days", they cried...

	A notable exception to this nonsense was an American planter named
Washington.  In the middle of the kerfuffle, he simply changed his birthdate
in the family bible from February 11 to February 22.  An eminently sensible
individual.

					Rick.

Article-I.D.: sdcrdcf.2212
Posted: Wed Jul 31 12:37:20 1985
Date-Received: Sun, 4-Aug-85 08:11:51 EDT
References: <2849@mordor.UUCP>
Reply-To: markb@sdcrdcf.UUCP (Mark Biggar)
Organization: System Development Corp. R+D, Santa Monica
Lines: 18
Summary: 

In article <2849@mordor.UUCP> @S1-A.ARPA,@MIT-MC.ARPA:mcgeer%ucbkim@Berkeley writes:
>	Incidentally, the world shifted to the Gregorian calendar at varying
>times.  The Roman Catholic world did it first, in the 16th Century -- but
>that was after the Schism, and so England didn't follow suit.  For 200 years
>England's calendar trailed the European by first 9, then 10, then 11 days.
>England finally converted in the mid-18th Century, to riots (11 days were
>dropped from the calendar at the stroke of a pen).  Russia converted after
>the Bolshevik revolution; this is why the "October revolution" was really
>held, by Western calendars, in November.

The British changeover (here to as we were still colonies) happened in
1752 (try running "cal 1752" and looking at Sep).  If I had been there
I would have rioted too.  People didn't object to the dropping of the
days form the calandar, what they objected to was that all the landlords
were charging a full months rent for Sep even though it was 11 days short.

Mark Biggar
{allegra,burdvax,cbosgd,hplabs,ihnp4,akgua,sdcsvax}!sdcrdcf!markb

Article-I.D.: fortune.5457
Posted: Fri Aug  9 21:56:37 1985
Date-Received: Tue, 13-Aug-85 00:58:46 EDT
References: <2849@mordor.UUCP> <2212@sdcrdcf.UUCP>
Reply-To: lowry@fortune.UUCP (John lowry)
Organization: Fortune Systems, Redwood City, CA
Lines: 3

I seem to recall reading that one or more of the Nordic countries
adjusted their calendar in a way that caused the minimum of difficulty:
they simply didn't have any leap years for about 40 years.