bakerre@tawc1.eglin.af.mil (Baker, Robert E.) (05/16/91)
I'm looking for source for a function that determines whether or not a year is a leap year. Anybody got it. ADVthanksANCE. +----------------------------------+------------------------------------------+ | Robert E. Baker | | | BAKERRE@TAWC1.EGLIN.AF.MIL | This space intentionally left blank | | USAF Tactical Air Warfare Center | | | "Bob's opinions are BOB's!" | | +----------------------------------+------------------------------------------+
dvlhma@cs.umu.se (Henrik Magnusson) (05/17/91)
In article <26912@adm.brl.mil> bakerre@tawc1.eglin.af.mil (Baker, Robert E.) writes: > > I'm looking for source for a function that determines whether or not a >year is a leap year. Anybody got it. ADVthanksANCE. > To determine if a year is a leap year or not is pretty easy. If the year is not a hundred (1988, 1989, 1990) then the year should be divisable with 4 to be a leapyear. If the year is a hundred (1800, 1900, 2000) then the year should be divisable with 400. Here is a quickly written function. FUNCTION is_leap_yeat(year :integer) :Boolean; BEGIN is_leap_year := ((year MOD 4) AND NOT (year mod 100)) OR (year MOD 400); END; /NeNNe ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :: Henrik Magnusson :: "How'd you puncture that tyre?" :: :: dvlhma@cs.umu.se :: "Ran over a milk bottle" :: :: :: "Didn't you see it?" :: :: Umeaa University, Sweden :: "Damn kid had it under his coat." :: :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
DAVID@ches.cs.vims.edu (05/17/91)
This should work as a leap year function:
function leap(year : integer) : boolean;
begin
if year mod 100 = 0 then
leap := year mod 400 = 0
else
leap := year mod 4 = 0
end;
This won't work historically, of course, for political and religious
reasons. The omission of century years not divisible by 400 was only
introduced with the Gregorian calendar in the 1500's. Thus 1700 was
not a leap year -- in Roman Catholic countries, but in England and the
American colonies, 1700 was a leap year. Russia only adopted the Gregorian
calendar this century so they did not miss in 1800 and 1900 either!
David Evans
david@ches.cs.vims.eduneile@hls.com (05/17/91)
In article <26912@adm.brl.mil>, bakerre@tawc1.eglin.af.mil (Baker, Robert E.) writes: > > I'm looking for source for a function that determines whether or not a > year is a leap year. Anybody got it. ADVthanksANCE. > The test for a leap year is simple; year mod 4 = 0. There is no reason to add complexity as indicated in other postings. Neil Everhart
dslg0849@uxa.cso.uiuc.edu (Daniel S. Lewart) (05/18/91)
neile@hls.com writes: > The test for a leap year is simple; year mod 4 = 0. There is no reason to > add complexity as indicated in other postings. Unless, of course, you want to do it correctly. Daniel Lewart d-lewart@uiuc.edu
reeses@milton.u.washington.edu (Feltch Master) (05/18/91)
In article <1991May17.074806.130@hls.com> neile@hls.com writes: >In article <26912@adm.brl.mil>, bakerre@tawc1.eglin.af.mil (Baker, Robert E.) writes: >> >> I'm looking for source for a function that determines whether or not a >> year is a leap year. Anybody got it. ADVthanksANCE. >> >The test for a leap year is simple; year mod 4 = 0. There is no reason to >add complexity as indicated in other postings. > >Neil Everhart Yes, there is a need for complexity...years divisible by 100 that are not also divisible by 400 are not leap years. 1900 was not a leap year, despite the fact that it was divisible by 4. 2000 will be, as will 2400, as will 2800, etc. Art Taylor -- ------------------------------------------------------------------------------- reeses@milton.u.washington.edu University of Washington, Seattle "Reality is a cop-out for people who can't handle drugs"
Jonathan.Bradshaw@thevoid.fidonet.org (Jonathan Bradshaw) (05/18/91)
In a message of <May 17 15:48>, UUCP (neile@hls.com U>The test for a leap year is simple; year mod 4 = 0. There is no reason to U>add complexity as indicated in other postings. Buzzz.. wrong, all centuries that are divisible by 4 are NOT leap years, only if they are divisible by 400... * Origin: VOIDian Gateway of Michiana (thevoid.fidonet.org) (1:227/1.6)
ins845b@monu4.cc.monash.edu.au (mr k.l. lentin) (05/18/91)
In article <1991May17.074806.130@hls.com> neile@hls.com writes: >In article <26912@adm.brl.mil>, bakerre@tawc1.eglin.af.mil (Baker, Robert E.) writes: >> >> I'm looking for source for a function that determines whether or not a >> year is a leap year. Anybody got it. ADVthanksANCE. >> >The test for a leap year is simple; year mod 4 = 0. There is no reason to >add complexity as indicated in other postings. > >Neil Everhart Not altogether true. All century years that are not multiples of 400 are NOT leap years so 1600 IS a leap year 1700,1800,1900 WERE and 2000 will be! If thats not a problem year mod 4 = 0 works fine. |/ |\evin
dvlhma@cs.umu.se (Henrik Magnusson) (05/18/91)
In article <1991May17.074806.130@hls.com> neile@hls.com writes: >In article <26912@adm.brl.mil>, bakerre@tawc1.eglin.af.mil (Baker, Robert E.) writes: >> >> I'm looking for source for a function that determines whether or not a >> year is a leap year. Anybody got it. ADVthanksANCE. >> >The test for a leap year is simple; year mod 4 = 0. There is no reason to >add complexity as indicated in other postings. > >Neil Everhart Sorry but it year MOD 4= 0 isn't enough. 1900 isn't a leapyear, but 2000 is! /NeNNe ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :: Henrik Magnusson :: "How'd you puncture that tyre?" :: :: dvlhma@cs.umu.se :: "Ran over a milk bottle" :: :: :: "Didn't you see it?" :: :: Umeaa University, Sweden :: "Damn kid had it under his coat." :: :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
kai@kaiki.toppoint.de (Kai Voelcker) (05/18/91)
neile@hls.com writes: > The test for a leap year is simple; year mod 4 = 0. There is no reason to > add complexity as indicated in other postings. > Neil Everhart And what's about 1900? That's n o t a leap year! ________________________________________________________________________ | Kai Voelcker, Kappelner Str 18, D-2300 Kiel 1, voice: +49 431 335605 | | kai@kaiki.toppoint.de interests: 386asm, c, pascal; OR algorithms | | >>> polite notice: I have to pay for incoming mail. Thanks <<< | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
hoffmann@infopls.chi.il.us (Robert Hoffmann) (05/19/91)
neile@hls.com writes: > > I'm looking for source for a function that determines whether or not a > > year is a leap year. Anybody got it. ADVthanksANCE. > The test for a leap year is simple; year mod 4 = 0. There is no reason to > add complexity as indicated in other postings. Sure there is. Several hundred years ago, the rules for century years (ones ending in 00) were changed... deleting 3 leap years every 400 years helps keep the calendar intact and the seasons happening on the right dates... If (year mod 100) = 0, then if (year mod 400) <> 0, it's not a leap year. That's why the complexity...
Kai_Henningsen@ms.maus.de (Kai Henningsen) (05/21/91)
neile @ hls.com schrieb am Fr 17.05.1991, 13:48 A16170@SUB in Cl-Pascal:
ne>The test for a leap year is simple; year mod 4 = 0. There is no reason to
ne>add complexity as indicated in other postings.
This, of course, assumes that you will never be interested in years before 1901
or after 2099. I would prefer not to make such an assumption. Then, the (still
simple) rule is of course
(year mod 4 = 0) and ((year mod 100 <> 0) or (year mod 400 = 0))
That's for the Gregorian calender. Once you leave *that* ground, it gets
complicated.
--
Kai Henningsen Internet: kh@ms.maus.de
Muenster UUCP: any_backbone_that_knows_domains!ms.maus.de!kh
Germany Fido: kh%maus ms, 2:242/2.6 or Kai Henningsen, 2:242/2.244g_harrison@vger.nsu.edu (George C. Harrison, Norfolk State University) (05/21/91)
In article <1991May18.112519.3371@monu0.cc.monash.edu.au>, ins845b@monu4.cc.monash.edu.au (mr k.l. lentin) writes: > In article <1991May17.074806.130@hls.com> neile@hls.com writes: >>In article <26912@adm.brl.mil>, bakerre@tawc1.eglin.af.mil (Baker, Robert E.) writes: >>> >>> I'm looking for source for a function that determines whether or not a >>> year is a leap year. Anybody got it. ADVthanksANCE. >>> >>The test for a leap year is simple; year mod 4 = 0. There is no reason to >>add complexity as indicated in other postings. >> >>Neil Everhart > > Not altogether true. All century years that are not multiples of 400 are NOT > leap years so 1600 IS a leap year 1700,1800,1900 WERE and 2000 will be! > If thats not a problem year mod 4 = 0 works fine. > > |/ > |\evin It really depends on the application. As a mathematician I'd like to see the total rule in effect, but consider this..... If the program was to run for the next 108 or so years continually, could the programmer be fired??? (assuming, of course, that the program was to determine the current day, etc. and not some day of the week that occured in history {before 1901}) I have a function which is really neat, but I am sure 1578 people have emailed it to him already. There are probably those who will post all date alterations (Julian calendar, etc.) since Adam and Eve and even since God first saw "that it was good." George.... -- George C. Harrison ----------------------- ----- Professor of Computer Science ----------------------- ----- Norfolk State University ----------------------- ----- 2401 Corprew Avenue, Norfolk, Virginia 23504 ----------------------- ----- INTERNET: g_harrison@vger.nsu.edu ---------------------------------
CDHWilli@exua.exeter.ac.uk (Charles Williams) (05/21/91)
>The test for a leap year is simple; year mod 4 = 0. There is no reason to >add complexity as indicated in other postings. > >Neil Everhart Isn't there something odd about the centuries and millenia?
d89mb@efd.lth.se (Magnus Bodin) (05/22/91)
>>The test for a leap year is simple; year mod 4 = 0. There is no reason to >>add complexity as indicated in other postings. >> >>Neil Everhart >Isn't there something odd about the centuries and millenia? Yes, sort of. Leap year occurs every year that is even dividable by 4, eg 1984, 1988, 1992... But, it does NOT occur when the year is even dividable by 100, eg. 1800, 1900 UNLESS it's not even dividable by 400 AS WELL... Therefore 2000 is a leap year. If you just divide by 4, you won't have wrong until 2100. Takelr|, Magnus -- Magnus Bodin "Nec fasces, nec opes, Institute of Tychology, sola artis sceptra perennant" Box 5127, 220 05 Sweden (Tycho Brahe, Stj{rneborg 1584)
acm@Sun.COM (Andrew MacRae) (05/23/91)
In article <15921@ms.maus.de>, Kai_Henningsen@ms.maus.de (Kai Henningsen) writes: > This, of course, assumes that you will never be interested in years before 1901 > or after 2099. I would prefer not to make such an assumption. Then, the (still > simple) rule is of course It's funny, but in close to fifteen years of programming I have yet to discover a need to handle dates before 1901 or after 2099. Of course I have only developed real-time systems, operating systems, compilers, linkers, and far too many data base applications. Other than a super duper calendar program or a star charting program, I am at a loss to think of a reason to go past those dates in either direction, at least for the purpose of finding the day of the week. In the forward direction, it is rather silly to believe that your pc (or your software) will still be in use in the year 2100. (Yes, yes, I know, maybe the person posting is building a machine that *is* supposed to last that long. Frankly I doubt it.) In the backward direction, the problem with the rule mentioned in the previous posting is that it only takes you back to the year 1722 (I think). That was the year that eleven days were dropped from the calendar. Unless you account for that you are still off. (I may be off on the exact year.) The only program that I am familier with that *does* handle those missing eleven days is a calendar program running (I think) under UNIX. Does anyone have an example (other than the two I mentioned above) where their program had to know the day of the week for a date before 1901 or after 2099? Andrew MacRae
marcos@allanon.UUCP (Marcos Della) (05/23/91)
kai@kaiki.toppoint.de (Kai Voelcker) writes: > neile@hls.com writes: > > The test for a leap year is simple; year mod 4 = 0. There is no reason to > > add complexity as indicated in other postings. > > Neil Everhart > > And what's about 1900? That's n o t a leap year! how about changing it to the following: leap_year := (year MOD 4 = 0) AND ((year MOD 100 <> 0) OR (year MOD 400 = 0)); That should clear up the hundred and four hundred year problem... Marcos ____________________________________________________________________________ Marcos R. Della | Did you ever wonder if there was allanon!marcos@petunia.CalPoly.EDU (home) | more to the universe than this? mdella@polyslo.CalPoly.EDU (school) | marcos.della@f185.n125.z1.fidonet.org | ...I didn't...
Robert_Salesas@mindlink.bc.ca (Robert Salesas) (05/23/91)
Yeah, I could just imagine the new watches coming out just for that particular day, I suppose that with digital watches there wouldn't be any problem... Rob -- \--------------------------------------------------------------------/ \ Robert Salesas + Usenet: Robert_Salesas@MINDLINK.bc.ca / \ Eschalon Development Inc. + CIS: 76625,1320 BYTE: newdawn / \--------------------------------------------------------------------/
defaria@hpcupt3.cup.hp.com (Andy DeFaria) (05/24/91)
I got an idea. The reason we even have a leap year at all is because a year is slightly more than 365 days. It's something like 365 days 5 hours 48 minutes and 46 seconds. Why not simply do away with leap day altogether and insert the 1/4 day after 12/31 of the year. Make is a variable length day to accomidate the changes in the earths rotation around the sun. Hell I'm sure that most people would enjoy the extra 1/4 for rest after a good New Years Party! :-)
acm@Sun.COM (Andrew MacRae) (05/24/91)
In article <JPRD34w164w@allanon.UUCP>, marcos@allanon.UUCP (Marcos Della) writes: > how about changing it to the following: > > leap_year := (year MOD 4 = 0) AND > ((year MOD 100 <> 0) OR (year MOD 400 = 0)); > > That should clear up the hundred and four hundred year problem... But it *doesn't* clear up the 1722 problem. (In 1722, eleven days were dropped out of the month of September.) I guess you could call 1722 a super duper negative leap year, that is in regular leap years one day is added. In a sdn leap year eleven days are dropped. It's a pity that they didn't drop them from February. Andrew MacRae
etxbjk@solsta.ericsson.se (Bjorn Karlsen TX/DKI) (05/24/91)
>In the backward direction, the problem with the rule mentioned in the previous >posting is that it only takes you back to the year 1722 (I think). That was >year that eleven days were dropped from the calendar. Unless you account for >that you are still off. (I may be off on the exact year.) The only program >that I am familier with that *does* handle those missing eleven days is a >calendar program running (I think) under UNIX. The year was 1752. Here's the output from UNIX' cal: 1752 Jan Feb Mar S M Tu W Th F S S M Tu W Th F S S M Tu W Th F S 1 2 3 4 1 1 2 3 4 5 6 7 5 6 7 8 9 10 11 2 3 4 5 6 7 8 8 9 10 11 12 13 14 12 13 14 15 16 17 18 9 10 11 12 13 14 15 15 16 17 18 19 20 21 19 20 21 22 23 24 25 16 17 18 19 20 21 22 22 23 24 25 26 27 28 26 27 28 29 30 31 23 24 25 26 27 28 29 29 30 31 Apr May Jun S M Tu W Th F S S M Tu W Th F S S M Tu W Th F S 1 2 3 4 1 2 1 2 3 4 5 6 5 6 7 8 9 10 11 3 4 5 6 7 8 9 7 8 9 10 11 12 13 12 13 14 15 16 17 18 10 11 12 13 14 15 16 14 15 16 17 18 19 20 19 20 21 22 23 24 25 17 18 19 20 21 22 23 21 22 23 24 25 26 27 26 27 28 29 30 24 25 26 27 28 29 30 28 29 30 31 Jul Aug Sep S M Tu W Th F S S M Tu W Th F S S M Tu W Th F S 1 2 3 4 1 1 2 14 15 16 5 6 7 8 9 10 11 2 3 4 5 6 7 8 17 18 19 20 21 22 23 12 13 14 15 16 17 18 9 10 11 12 13 14 15 24 25 26 27 28 29 30 19 20 21 22 23 24 25 16 17 18 19 20 21 22 26 27 28 29 30 31 23 24 25 26 27 28 29 30 31 Oct Nov Dec S M Tu W Th F S S M Tu W Th F S S M Tu W Th F S 1 2 3 4 5 6 7 1 2 3 4 1 2 8 9 10 11 12 13 14 5 6 7 8 9 10 11 3 4 5 6 7 8 9 15 16 17 18 19 20 21 12 13 14 15 16 17 18 10 11 12 13 14 15 16 22 23 24 25 26 27 28 19 20 21 22 23 24 25 17 18 19 20 21 22 23 29 30 31 26 27 28 29 30 24 25 26 27 28 29 30 31 -- ========================================================================= Bj|rn Karlsen etxbjk@solsta.ericsson.se Ericsson Telecom etx.etxbjk@memo.ericsson.se S-652 21 Karlstad, SWEDEN etxbjk@lmej.ericsson.se ========================================================================= "Det einaste eg var stiv i p} skulen, var nakken" - Trond Kirkvaag
jja@wsl.ie (John Allen on wsl) (05/24/91)
In article <4165@jethro.Corp.Sun.COM> acm@Sun.COM (Andrew MacRae) writes: >It's funny, but in close to fifteen years of programming I have yet to discover >a need to handle dates before 1901 or after 2099. Of course I have only How about a hospital records system, you know some people that were born before 1901 are still alive today. As I keep saying there is no reason to do anything incorrectly when it's just as easy to do it right. ----------------------------------------------------------------------------- |\/\/\/| | | | (-)(o) | _) | ,___| | / /____\ And the BART raised up his hands and said unto the masses. People that don't know want to know from the people that do know and if the poeple that do know don't tell the people that don't know then the people that don't know still won't know. "Don't quote me on any issue whatsoever, unless you feel oblidged to."
R.Smithers@ee.surrey.ac.uk (Russell Smithers) (05/24/91)
neile@hls.com writes: > The test for a leap year is simple; year mod 4 = 0. There is no reason to > add complexity as indicated in other postings. > Neil Everhart And what's about 1900? That's n o t a leap year! ________________________________________________________________________ | Kai Voelcker, Kappelner Str 18, D-2300 Kiel 1, voice: +49 431 335605 | | kai@kaiki.toppoint.de interests: 386asm, c, pascal; OR algorithms | | >>> polite notice: I have to pay for incoming mail. Thanks <<< | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Actualy I saw something resantly about this exact problem i think it was c code but I noticed its not just mod 4 its a check with mod 100. Ill dont think I can find the artical any more but its not that much, its about 3 -4 lines of code max with an if else if I remember! Any way im sure someone else will post the answer.
Conrad.Bullock@comp.vuw.ac.nz (Conrad Bullock) (05/25/91)
In article <1991May25.031535.1054@cs.mcgill.ca>, einstein@cs.mcgill.ca (Michael CHOWET) writes: |> So, getting back to the original purpose of this post, the function |> would |> look more like: |> |> function LEAPYEAR ( year : integer ) : boolean ; |> |> begin |> |> LEAPYEAR := ( year mod 100 <> 0 ) and ( year mod 4 = 0 ) ; |> |> end { of function LEAPYEAR } ; I think that there is an additional rule - if a year is divisible by 400, then it IS a leap year - so 2000 is divisible by 4, so it is a leap year, but it is divisible by 100, so it ISN'T a leap year, but it is divisible by 400, so it IS a leap year. This rule is significant, with 2000 coming up. If you just forget about the whole lot, and use being divisible by 4, then your program will work until the year 2100. -- Conrad Bullock | Domain: conrad@comp.vuw.ac.nz Victoria University of Wellington, | or: conrad@cavebbs.gen.nz New Zealand. | Fidonet: 3:771/130 | BBS: The Cave BBS +64 4 643429
marcos@allanon.UUCP (Marcos Della) (06/03/91)
acm@Sun.COM (Andrew MacRae) writes: >In article <JPRD34w164w@allanon.UUCP>, marcos@allanon.UUCP (Marcos Della) >> how about changing it to the following: >> ... > > But it *doesn't* clear up the 1722 problem. (In 1722, eleven days were > dropped out of the month of September.) > You know, I didn't know about the 1722 year. What month did they drop out the days from? Or did they just shorten all the months except February. Also, why the heck di they do it and why that particular year? Marcos ____________________________________________________________________________ Marcos R. Della | Did you ever wonder if there was allanon!marcos@petunia.CalPoly.EDU (home) | more to the universe than this? mdella@polyslo.CalPoly.EDU (school) | marcos.della@f185.n125.z1.fidonet.org | ...I didn't...
baillie@mullauna.cs.mu.OZ.AU (Stephen Baillie) (06/05/91)
marcos@allanon.UUCP (Marcos Della) writes: >acm@Sun.COM (Andrew MacRae) writes: >>In article <JPRD34w164w@allanon.UUCP>, marcos@allanon.UUCP (Marcos Della) >>> how about changing it to the following: >>> ... >> >> But it *doesn't* clear up the 1722 problem. (In 1722, eleven days were >> dropped out of the month of September.) ^^^^^^^^^ - Note this ? >> >You know, I didn't know about the 1722 year. What month did they drop out the >days from? Or did they just shorten all the months except February. See the indicated section above? Good. >Also, why the heck di they do it and why that particular year? It was because of a discrepancy between the number of days in a year in the old (Julian?) Calendar, ie one without leap years, and the actual passage of the earth around the sun (did I get that the right way around? ;-> ) The year was out of sync with the sun by 11 days, so at the same time as introducing leap years they cut a few days to make things line up again. Caused quite a stir among the superstitious peasants who thought they were losing a few days out of their lives! I think that pre-1722 there were no leap years, so your program may try to compensate for this too. Steve. "If we shadows have offended, Think but this and all is mended: That you have but slumbered here, While these visions did appear. And this weak and idle theme, no more yielding but a dream." baillie@mullauna.cs.mu.oz.au (Stephen Baillie)
oep@gi.uio.no (Oeyvind Pedersen) (06/06/91)
In article <baillie.676098437@mullauna>, baillie@mullauna.cs.mu.OZ.AU (Stephen Baillie) writes: > It was because of a discrepancy between the number of days in a year in the > old (Julian?) Calendar, ie one without leap years, and the actual passage > of the earth around the sun (did I get that the right way around? ;-> ) > > The year was out of sync with the sun by 11 days, so at the same time as > introducing leap years they cut a few days to make things line up again. > Caused quite a stir among the superstitious peasants who thought they > were losing a few days out of their lives! > > I think that pre-1722 there were no leap years, so your program may try to > compensate for this too. The Julian calendar HAD leap years. The problem was that it had too many - 25 in each century, while the Gregorian calendar has 24.25, that is 24 in three centuries and 25 in the fourth. That makes an average year 365.2425 days long instead of 365.25, while the "real" year, i.e the time the earth uses in one lap is about 365.2422 days. Oeyvind.
cssjs2@ufhx1 (Mr JM Scheepers) (06/06/91)
In <a4Dy31w164w@allanon.UUCP> marcos@allanon.UUCP (Marcos Della) writes: >acm@Sun.COM (Andrew MacRae) writes: >>In article <JPRD34w164w@allanon.UUCP>, marcos@allanon.UUCP (Marcos Della) >> But it *doesn't* clear up the 1722 problem. (In 1722, eleven days were >> dropped out of the month of September.) >> >You know, I didn't know about the 1722 year. What month did they drop out the >days from? Or did they just shorten all the months except February. >Also, why the heck di they do it and why that particular year? >Marcos The Julian calendar (after Caesar) was introduced in 45 BC, but because of its simple rules for leap years, Pope Gregory XIII introduced changes to correct the discrepancy. He decreed that Thursday, October 4, 1582 would be followed by Friday, October 15. The British Empire only accepted this in 1752, and Russia only after the revolution, in 1918. A function for calculating leap years would be: function Leap(y: year): boolean; begin Leap := (y mod 4 = 0) and ((y mod 100 <> 0) or (y mod 400)=0)) end -- Inus Scheepers | Internet cssjs2@ufhx1.ufh.ac.za |Disclaimer: Is it my fault Dept Comp Sci | Phone +27 404 32011 x 2488 | that power walks on Univ Fort Hare | Fax +27 404 31669 | crooked legs? P/Bag X1314, Alice 5700, Ciskei, South Africa |
ts@uwasa.fi (Timo Salmi) (06/07/91)
In article <a4Dy31w164w@allanon.UUCP> marcos@allanon.UUCP (Marcos Della) writes: : >You know, I didn't know about the 1722 year. What month did they drop out the >days from? Or did they just shorten all the months except February. > >Also, why the heck di they do it and why that particular year? : I seem to recall that the information can be found in Numerical Recipes. ................................................................... Prof. Timo Salmi Moderating at garbo.uwasa.fi anonymous ftp archives 128.214.12.37 School of Business Studies, University of Vaasa, SF-65101, Finland Internet: ts@chyde.uwasa.fi Funet: gado::salmi Bitnet: salmi@finfun
Kai_Henningsen@ms.maus.de (Kai Henningsen) (06/08/91)
Stephen Baillie baillie%mullauna.cs.mu.OZ.AU @ SUB schrieb am Mi 05.06.1991, 03:07 A18353@SUB in Cl-Pascal: SB>It was because of a discrepancy between the number of days in a year in the SB>old (Julian?) Calendar, ie one without leap years, and the actual passage SB>of the earth around the sun (did I get that the right way around? ;-> ) In fact, no .. see below. SB>The year was out of sync with the sun by 11 days, so at the same time as SB>introducing leap years they cut a few days to make things line up again. SB>Caused quite a stir among the superstitious peasants who thought they SB>were losing a few days out of their lives! That, however, is ok ... SB>I think that pre-1722 there were no leap years, so your program may try to SB>compensate for this too. It's like this: before the Gregorian calender, we had the Julian calender, so named after one Julius Caesar, I believe, who in the year 46 BC reformed the then-without-leap-years calender to include one every four years - this made a calendar year of 365.25 days instead of 365. (That's why we have a month called july: before, it was quintilis ...) As the actual year length is more like 365.2422, however, this still caused problems. In 1582 (not 1722) pope Gregor the umpteenth decided enough was enough, dropped the 5.-14. october(!) and invented some more leap days, bringing the year to 365.2425 days. The difference of about 0.0003 days/year makes an error of one day in 3000 years - we might as well forget that :-) However, there is more. Not every nation accepted Gregor's decision at once. Russia, for example, officially adopted the Julian(!) calender as late as 1.1.1700(!) (tsar Peter the great), then dropped 13 days at the start of february 1918(!) to switch to Gregorian. I think they were the last to do it, and nowadays nobody uses the Julian calender any more. -- Kai Henningsen Internet: kh@ms.maus.de Muenster UUCP: any_backbone_that_knows_domains!ms.maus.de!kh Germany Fido: kh%maus ms, 2:242/2.6 or Kai Henningsen, 2:242/2.244
cctr132@csc.canterbury.ac.nz (Nick FitzGerald, CSC, Uni. of Canterbury, NZ) (06/08/91)
In article <1991Jun6.083418.9559@ulrik.uio.no>, oep@gi.uio.no (Oeyvind Pedersen) writes: > The Julian calendar HAD leap years. The problem was that it had too > many - 25 in each century, > while the Gregorian calendar has 24.25, that is 24 in three centuries > and 25 in the fourth. > That makes an average year 365.2425 days long instead of 365.25, while > the "real" year, i.e > the time the earth uses in one lap is about 365.2422 days. I know this is getting way off-topic for this group, but the obvious question now arises: What happens to these "additional" .0003 days? Do they just accumulate, putting us further and further out of kilter but more slowly than the excessive Julian leap years? I've heard of "leap seconds" (yeah, no kidding) - are these anything to do with it? --------------------------------------------------------------------------- Nick FitzGerald, PC Applications Consultant, CSC, Uni of Canterbury, N.Z. Internet: n.fitzgerald@csc.canterbury.ac.nz Phone: (64)(3) 642-337
acm@Sun.COM (Andrew MacRae) (06/11/91)
In article <baillie.676098437@mullauna>, baillie@mullauna.cs.mu.OZ.AU (Stephen Baillie) writes: > The year was out of sync with the sun by 11 days, so at the same time as > introducing leap years they cut a few days to make things line up again. > Caused quite a stir among the superstitious peasants who thought they > were losing a few days out of their lives! As the one who first mentioned the dropping of 11 days from the calendar, I should also mention that (as several people have emailed me to say) the year that England and its colonies dropped 11 days from September was 1752, not 1722 as I had misremembered. It caused more that just a stir among superstitious peasants. It seems that landlords felt justified in collecting a full month's rent while employers felt just as justified in not paying for those 11 days! There were several days of rioting with people in the street shouting 'Give us back our days!'. It all goes to show just how fluid our calendars are. England dropped those 11 days in 1752. Other countries dropped them at other times. Those of you out there trying to create the 'perfect' formula for calculating leap year should remember to take into account what country the calculation is for. Andrew MacRae
DAVID@ches.cs.vims.edu (06/11/91)
Where do the elusive 0.0003 days go? I quote from "Tables of Physical and Chemical Constants", G.W.C.Kaye & T.H.Laby, Longmans. "The mean length of a year in this [the Gregorian] calendar is thus 365.2425 days, which is so near the present actual value that the date when it will appear to future generations expedient to replace one further Leap Year by an ordinary one is not yet clearly specifiable." The "leap seconds" have to do with the varying rate of rotation of the _earth_ and keep the solar day in synchronism with the standard atomic clocks. Leap years, on the other hand, have to do with the time taken for the earth to orbit the sun. Another nasty wrinkle about the calendar is that before the 1700's, the year changed at dates different from January 1. Which day dependent on which country you were in and even in one country things changed over time. In England, for a while, things were standardized so that March 25 (one of the quarter days) began the year, thus March 24, 1666 was followed by March 25, 1667. On tombstones you sometimes see dates like January 25, 1650/51. David Evans, Virginia Institute of Marine Science DAVID@CHES.CS.VIMS.EDU
dmurdoch@watstat.waterloo.edu (Duncan Murdoch) (06/11/91)
In article <4331@jethro.Corp.Sun.COM> acm@Sun.COM (Andrew MacRae) writes: > >It all goes to show just how fluid our calendars are. England dropped >those 11 days in 1752. Other countries dropped them at other times. Those of >you out there trying to create the 'perfect' formula for calculating leap year >should remember to take into account what country the calculation is for. One other weird complication: before England made the calendar change, years ran from March to February, not January to December. This makes it really hard to know exactly when certain people (e.g. Thomas Bayes) were born: if they died after the calendar change, but were said to have been born in February 1701, was that before or after March 1701? And, more to the point of the subject heading (but still not much to do with Pascal; sorry), do programs calculating leap years take into account that there was no February in 1752 in England? (Or was there?) Duncan Murdoch
mowl@pippin.cc.flinders.edu.au (Wolfgang Lieff) (06/11/91)
In article <4331@jethro.Corp.Sun.COM> acm@Sun.COM (Andrew MacRae) writes: > >It all goes to show just how fluid our calendars are. England dropped >those 11 days in 1752. Other countries dropped them at other times. Those of >you out there trying to create the 'perfect' formula for calculating leap year >should remember to take into account what country the calculation is for. > To come back to programming - I think it's clear now, that the 'perfect' leap year function would not be a mathematical one but a communications program dialing up a 'national time and date standard service'. And still, how do we take care of the future ? What about the change to the decimal (ten month/year) system in 3291 ? Have fun, Wolfgang Wolfgang Lieff , mowl@cc.flinders.edu.au
jfh@vax.oxford.ac.uk (06/11/91)
The Julian-Gregorian transition certainly depends on what country you're thinking of; it can depend on what part of what country (e.g. Alaska, which changed when USA bought it from Russia). See the Explanatory Supplement to the Nautical Almanac and Astronomical Ephemeris (or is it the ES to the AE and NA - I don't have a copy by me) for a long list. Of course real computer people will have programmed the dates of Easter (both Western and Orthodox), Passover, Ramadan, ... as well.