The Museum of HP Calculators

HP Forum Archive 15

 Data arithmetic / elapsed days calculation programMessage #1 Posted by Stephen Easterling on 28 Sept 2005, 3:32 p.m. Does anyone have a basic program for calculating elapsed days between two given dates? I would like to run this program on a 15C, 33S or any Pioneer series model, and a 48-series.

 Re: Data arithmetic / elapsed days calculation programMessage #2 Posted by bill platt on 28 Sept 2005, 3:47 p.m.,in response to message #1 by Stephen Easterling That seems like a "data-intensive" program. Can you make a good alogrythm? Try july31 1947 to april 6, 2004. I guess I would write a supbroutine that 1st figures out the "day number". So you do 31 4 1947 GSB(x) and calculates days through march---how to store that----a series of if/then could build essentially a "lookup table" so that with "4" it returns 90 days--what about the leap years--a nested if/then for that? Then you add the days to the month "lookup table reuslt" and that is stored in a register, as is the start year. Then you run the same thing for the second date. Then the years subtract--oh, we need a leap year figurer for that part, too. I think this is too much memory for hte 15c, but it would fit in the 33s and the 48g. I am sure there is a program for (on the 48 and 49) this available at hpcalc.org. Regards

 You're joking, right ? :-)Message #3 Posted by Valentin Albillo on 29 Sept 2005, 4:18 a.m.,in response to message #2 by bill platt Hi, Bill: Bill wrote: ``` "I think this is too much memory for hte 15c, but it would fit in the 33s and the 48g." ``` You're joking, right ? The HP-15C can do this sort of calculation using 1/10th of its programming resources, at most. As for the 33s and its 32 Kb of RAM, try and invert an 8x8 matrix using it. The 0.4 Kb HP-15C can do that directly from the keyboard. Best regards from V.

 Re: You're joking, right ? :-)Message #4 Posted by bill platt on 29 Sept 2005, 8:52 a.m.,in response to message #3 by Valentin Albillo Hi Valentin, Glad I got your attention; I have not conversed with you in some time :-) Well, seeing that some here are more clever than me, yes indeed it looks like you can easily fit the problem into a 15c. I am afraid that my stream-of-consciousness idea of a solution would never fit into the 15c. Yet another example of how much more effective brains (15c, excellent built-in resources, efficient memory allocation) wins over brawn (33s, gobs of memory, difficulty using most of it) any day. On this day, I fit into the brawn category :-( Regards, Bill

 Re: You're joking, right ? :-)Message #5 Posted by Gerson W. Barbosa on 29 Sept 2005, 9:45 p.m.,in response to message #4 by bill platt Hi Bill, folks, Valentin is right: a DAYS BETWEEN DATES program does fit in the 15C memory. It even fits in the 11C memory. The following program has 140 lines and includes DAY OF WEEK as well (Of course Valentin would need only half of these, or even less if he manages to concoct a more amazing formula :-) . This is a direct implementation of the formulas used by the Master Library Module of the TI-59 calculator, one of my earliest 15C program, so do not expect anything close to perfection, quite the contrary! (Apparently, at the time I did not know what LSTx was for. I would also sometimes use 2 10^x instead of 100 just to save a step, even though this just makes the program slower, sometimes in the same program I would use simply 100). ``` f LBL 0 x<>y STO 0 x<>y ENTER g INT STO 1 Rv RCL 1 - 2 10^x * ENTER g INT STO 2 Rv f FRAC 4 10^x * STO 3 2 ENTER RCL 2 g TEST 7 GTO 1 RCL 3 ENTER 1 - 100 / 1 + g INT .75 * g INT CHS ENTER RCL 3 ENTER 1 - 4 / g INT + RCL 2 ENTER 1 - 31 * + RCL 1 + RCL 3 ENTER 365 * + g RTN f LBL 1 RCL 3 ENTER 365 * RCL 1 + RCL 2 ENTER 1 - 31 * + RCL 2 ENTER .4 * 2.3 + g INT - RCL 3 ENTER 4 / g INT + RCL 3 ENTER 100 / 1 + .75 * g INT - g RTN f LBL A GSB 0 RCL 0 GSB 0 RCL 0 - CHS g RTN f LBL B GSB 0 ENTER CHS ENTER 7 / g INT 7 * + g RTN ``` f A works just like the DeltaDYS on the 12C, when D.MY format is set. Unlike the DATE function on the 12C, f B requires only one argument (the date) and returns 0=Sat, 1=Sun, ... 6=Fri. This is quite handy in Portuguese as the days of the week are the corresponding ordinal numbers from Monday (segunda = 2nd) to Friday (sexta = 6th) :-) Example: 01.012005 ENTER 31.122005 f A => 364 29.092005 f B => 5 'Today is quinta-feira, oops, Thursday!' Regards, Gerson. ----------------------------- Notes: 1) The listing is supposed to be ok as I have just keyed it in the 11C and it worked. The program seems to be ok too. Of course g TEST 7 should be replaced by f x>y on the 11C. For speed, occurrences of 2 10^x and 4 10^x should be replaced by 100 and 10000 (or 100 g x^2), respectively. 2) The Brazilian edition of the TI-59/59 Master Library Module Manual has some typos (missing parentheses and brackets). I think the pencil annotation I made is correct: ```if m < 3 then f:=365a + d + 31(m-1) + int ((a-1)/4)-int(3/4(int((a-1)/100)+1)) else f:=365a + d + 31(m-1) + int(a/4) - int(3/4(int(a/100) + 1)) - int(0.4m + 2.3) day of week = f + (int(-f/7)*7) a=year; m=month; d=day ``` A funny mistranslation in this manual: The HI-LO GAME (ML-21) was translated as JOGO: Alô? Veja! (GAME: Hello? Look!) which made no sense at all! Apparently, the translator thought LO was short for 'LOOK' and HI was just the interjection 'hi'. (Edited to correct a couple of typos - I never get rid of them!) (Edited again to include a missing g INT in third line) ---------- To the list of beginner's mistakes in this program, I have to mention at least ten unnecessary ENTERs :-) There's going to be a cleaner version below in the thread. Edited: 1 Oct 2005, 1:19 a.m.

 Re: Data arithmetic / elapsed days calculation programMessage #6 Posted by don wallace on 29 Sept 2005, 6:24 a.m.,in response to message #2 by bill platt Hi all, Hi Bill. Good question, Stephen. I'm into astronomy, so also into this stuff... (JD etc...) One thing about the forum, you sure get some REALLY GOOD ANSWERS! Even if you were on a desert island and had no calculator, it's easy to work out how many days old you are (that is also sobering...we are a bit ephemeral, imho). You just work out what the leap years are (easy since if they divide into four they are, except for years divisible by 400). Make a small list of them (a single small look up table). You just then some simple work (30days hath september...) to get from start day/month to end day month (ignoring years). Add to this the 365 x number of years between the dates (if more than 1) and finally, count how many leap years are in between, adding one day for each leap year. There's your answer. Nearly do it in your head... DW

 Re: Data arithmetic / elapsed days calculation programMessage #7 Posted by James M. Prange (Michigan) on 28 Sept 2005, 3:54 p.m.,in response to message #1 by Stephen Easterling For the 48 (and 49) series, you can use the DDAYS command, as long as the dates are from October 15th, 1582 through December 31st, 9999. With system flag -42 clear, the arguments should be formatted as MM.DDYYYY, and with flag -42 set, the format is DD.MMYYYY. Regards,James

 HP48 Day-of-week (was: Data arithmetic / elapsed days calculation program)Message #8 Posted by Vieira, L.C. (Brazil) on 30 Sept 2005, 5:09 p.m.,in response to message #7 by James M. Prange (Michigan) Hi; the day-of-week (DOW in the HP41CX or HP41 Time Module) in the HP48G may be obtained with TSTR (Time STRing). A brief description of TSTR can also be found here: HP48GII Users´s Guide (chapter 25). TSTR uses the contents in both Level 2 (time stamp) and Level 1 (date reference) to compose a string (ALGEBRAIC mode demands arguments in the same order),. Given that both contents are valid, the resulting string (Level 1) is added a three-character reference head for the day-of-week (MON, TUE, WED...). Cheers. Luiz (Brazil) Edited: 30 Sept 2005, 5:14 p.m.

 Re: HP48 Day-of-week (was: Data arithmetic / elapsed days calculation program)Message #9 Posted by Gerson W. Barbosa on 30 Sept 2005, 6:42 p.m.,in response to message #8 by Vieira, L.C. (Brazil) Quote: Given that both contents are valid, the resulting string (Level 1) is added a three-character reference head for the day-of-week (MON, TUE, WED...). Hi Luiz, TSTR is very handy, but the output is in English. What about days of the week in languages other than English, like good ol' Portuguese, for instance? << "SábDomSegTerQuaQuiSex" 1.012 ROT DDAYS 7 MOD 3 * 1 + DUP 2 + SUB >> Flag -42 setting is irrelevant! Just enter the date according to the date format on your calculator: 30.092005 => "Sex" (sexta-feira) Replace "SabDomSegTerQuaQuiSex" with your favorite string: ```"SamDimLunMarMerJeuVen" "SabDomLunMarMerGioVen" "SábDomLunMarMiéJueVie" "SâmDumLunMarMieJoiVin" "SatSunMonTueWedThuFri" "SamSonMonDieMitDonFre" "ZatZonMaaDinWoeDonVri" "LörSönManTisOnsTorFre" "LauSunMaaTiiKesTorPer" "SobNiePonWtoSroCzwPia" ``` etc... Cheers, Gerson.

 Re: Data arithmetic / elapsed days calculation programMessage #10 Posted by Gunnar Degnbol on 28 Sept 2005, 5:14 p.m.,in response to message #1 by Stephen Easterling I don't have a calculator program, but it is fairly easy: 1) Move new year to the first of march, so that march is month 0 and february is month 11 of the previous year. 2) Compute the days since some day in january 1 BC as dn = year DIV 400 - year DIV 100 + year * 1461 DIV 4 + month * 153 DIV 5 + dayofmonth DIV is integer division, a very useful operation on the HP 33S (but easy to substitute with divide and INTG). 3) Do this for both dates and subtract the results. If you want the day of week, this can be reduced to dow = (year DIV 400 - year DIV 100 + year * 5 DIV 4 + month * 13 DIV 5 + dayofmonth) MOD 7 This is called Zeller's congruence. You can ignore the year DIV 400 - year DIV 100 part if you are only interested in the 20th and 21st centuries.

 Re: Data arithmetic / elapsed days calculation programMessage #11 Posted by htom on 28 Sept 2005, 5:48 p.m.,in response to message #10 by Gunnar Degnbol Convert each to Julian Day Numbers and subtract. http://scienceworld.wolfram.com/astronomy/JulianDate.html Or if you can limit your range, use the Modified Julian Day Numbers (note that these change at midnight, not noon!) http://scienceworld.wolfram.com/astronomy/ModifiedJulianDate.html

 Re: Data arithmetic / elapsed days calculation programMessage #12 Posted by Stephen Easterling on 28 Sept 2005, 8:21 p.m.,in response to message #11 by htom Thanks (everyone) for a terrific response. I knew it had something to do with Julian date, but I was wondering if there were other ways since some of these calcs keep time / date.

 Re: Data arithmetic / elapsed days calculation programMessage #13 Posted by Bram on 29 Sept 2005, 5:38 a.m.,in response to message #12 by Stephen Easterling Quote: (...), but I was wondering if there were other ways since some of these calcs keep time / date. You do know that the HP-12C even has a button to calculate days between dates, don't you?

 Re: Data arithmetic / elapsed days calculation programMessage #14 Posted by Stephen Easterling on 29 Sept 2005, 12:23 p.m.,in response to message #13 by Bram Yeah, I have the 12C and love this feature about it. I have several other HPs that calculate elapsed days. For the ones that don't calculate this, I want to write a short program to calculate it. Reason: I'm a medical physicist and frequently I need to calculate elapsed days for a cancer patient's treatment (from start to finish). This is most helpful for the physicians, really, but I have to "QA" every patient's chart weekly. For years I either do it in my head or manually (but using a calc). Now I'm learning to think smarter (or just being lazy!). I think I will first try the Modified Julian Date method since it seems easier. I have over a dozen new HPs added to my collection and trying to rotate them in/out of use (at home and at work) and need them to do what I want them to do. (My first HP was a 28S in '89 and cut my teeth on it.)

 Re: Data arithmetic / elapsed days calculation programMessage #15 Posted by Gerson W. Barbosa on 30 Sept 2005, 12:27 p.m.,in response to message #14 by Stephen Easterling Meanwhile, you can use the 15C program above. It is no masterpiece but it works! In testing it, I can see that today I am exactly 16141 days old, a prime number. And that I got married on a Wednesday (11/11/1987, all prime numbers too... but that was not on purpose), which matches what I can remember. To use the MM.DDYYYY format you're used to, just replace the first two lines with these: ```f LBL 0 x<>y STO 0 x<>y ENTER g INT STO 2 Rv RCL 2 - 100 * ENTER g INT STO 1 Rv f FRAC 4 10^x * STO 3 2 ENTER RCL 2 g TEST 7 ``` Best regards, Gerson.

 Re: Data arithmetic / elapsed days calculation programMessage #16 Posted by Andrés C. Rodríguez (Argentina) on 28 Sept 2005, 7:27 p.m.,in response to message #1 by Stephen Easterling A simple program appears in the HP25 Applications Handbook; a more sophisticated version is published in the HP41 Applications Pac. The HP25 version is quite simple, due to the limitations of that model (one of my favorites, indeed!). If you would like to understand how it works, and then adapt it to other machines, it may be a very appropriate starting point.

 Re: Data arithmetic / elapsed days calculation program: HP 42SMessage #17 Posted by R Lion (Spain) on 29 Sept 2005, 2:22 a.m.,in response to message #16 by Andrés C. Rodríguez (Argentina) I wrote a version of this prg for the 42S and I like very much how it works. Feel free for asking if interested. Raul

 Re: Data arithmetic / elapsed days calculation program: HP 42SMessage #18 Posted by Stephen Easterling on 29 Sept 2005, 12:25 p.m.,in response to message #17 by R Lion (Spain) Yeah, I'm interested. I have a 42S, too, and would like to rotate it in/out of professional / home use and be able to calculate elapsed days. If it makes it easier, my email address is.... s_easterling@earthlink.net Thanks! Stephen Melbourne, FL

 Re: Data arithmetic / elapsed days calculation programMessage #19 Posted by Meindert Kuipers on 29 Sept 2005, 2:50 p.m.,in response to message #16 by Andrés C. Rodríguez (Argentina) Also check out the PPC ROM Manual (for the HP41) for the functions CJ and JC, these have an excellent backgrounder. These work with both Julain and GRegorian calendars. Meindert

 The PPC ROM versions are very goodMessage #20 Posted by Gene Wright on 29 Sept 2005, 5:31 p.m.,in response to message #19 by Meindert Kuipers And are a good starting point for all this. Not very long and they work.

 Re: Data arithmetic / elapsed days calculation programMessage #21 Posted by Vassilis Prevelakis on 30 Sept 2005, 12:30 a.m.,in response to message #1 by Stephen Easterling Have a look at the Calendar Functions program for the HP-67/97 Its quite readable and well documented **vp

 Data arithmetic for 42S and 41Message #22 Posted by R Lion (Spain) on 30 Sept 2005, 2:21 a.m.,in response to message #21 by Vassilis Prevelakis I was wrong above: the program I adapted for the 42S, is this one for the 67 of the software library. I also wrote a version for the 41. Raul

 Watch out for Y2KMessage #23 Posted by Palmer O. Hanson, Jr. on 30 Sept 2005, 9:43 p.m.,in response to message #22 by R Lion (Spain) It might be appropriate to be careful about using days beween dates programs from the 1900's since many of those programs did not recognize that the year 2000 would be a leap year (the Y2K problem). If you translate one of those old programs you should check that the number of days between 01/01/2000 and 01/01/2001 is 366. The routine from the TI-59 Master Library mentioned in Gerson Barbosa's submission gets 366. If you are a dedicated purist, and what RPNer isn't, you might want to check the number of days the routine finds between 01/01/4000 and 01/01/4001. It should be 365. The routine from the TI-59 Master Library gets 366, but everyone knows that AOSers aren't purists.

 Re: Watch out for Y2KMessage #24 Posted by Gerson W. Barbosa on 30 Sept 2005, 11:01 p.m.,in response to message #23 by Palmer O. Hanson, Jr. 4000 will be a leap year since it is divisible by 400, won't it? Anyway, the program fails for 1700, 1800, 2100, 2200, etc. However I am not sure whether this is due to something wrong in the TI-59 Master Library routine or in the 15C program since I don't have a TI-59. The 12C returns 365 for 01/01/2100-01/01/2101 and 366 for 01/01/4000-01/01/4001. ----- I have just checked 01/01/2100-01/01/2101 and 01/01/4000-01/01/4001 on Miroslav Nemecek's TI-59 Emulator and the results match those of the 12C. I have to see what is causing the 15C program to return 366 for 01/01/2100-01/01/2101. Edited: 30 Sept 2005, 11:36 p.m.

 Day of Week & Days Between Dates - Lighter version (Was Re: Watch out for Y2K)Message #25 Posted by Gerson W. Barbosa on 1 Oct 2005, 2:25 a.m.,in response to message #24 by Gerson W. Barbosa There was just a missing g INT in the third line. Here is a 15C lighter version after removing a lot of unneeded ENTER's: ``` 001: f LBL 0 x<>y STO 0 x<>y ENTER g INT STO 2 Rv RCL 2 - 100 * ENTER 016: g INT STO 1 Rv f FRAC 4 10^x * STO 3 2 ENTER RCL 2 g TEST 7 028: GTO 1 RCL 3 1 - 100 / 1 + g INT .75 * g INT CHS RCL 3 046: 1 - 4 / g INT + RCL 2 1 - 31 * + RCL 1 + RCL 3 365 * + 067: g RTN 068: f LBL 1 RCL 3 365 * RCL 1 + RCL 2 1 - 31 * + RCL 2 .4 * 2.3 + 091: g INT - RCL 3 4 / g INT + RCL 3 100 / 1 + .75 * g INT - 111: g RTN 112: f LBL A GSB 0 RCL 0 GSB 0 RCL 0 - CHS 119: g RTN 120: f LBL B GSB 0 ENTER CHS 7 / g INT 7 * + 130: g RTN ``` Date format is MM.DDYYYY f A: works just like the DeltaDYS on the 12C. f B: similar to DATE on the 12C, but requires only one argument, the date, and returns 0=Sat, 1=Sun, ... 6=Fri. On the 11C, g TEST 7 should be replaced with f x>y Everything appears to be all right now. Sorry for the inconvenience.

 When does a calendar week start? (was: Day of Week & Days Between Dates - Lighter version)Message #26 Posted by James M. Prange (Michigan) on 1 Oct 2005, 3:41 a.m.,in response to message #25 by Gerson W. Barbosa I notice that you have Saturday=0 through Friday=6, but ISO 8601 defines the day of week numbers as Monday=1 through Saturday=7, presumably in accordance with European calendars starting the week on Monday. Here in the U.S.A., our calendars have stuck with the tradition of the week starting on Sunday, so the ISO numbers seem very strange. Just out of curiosity, of the cultures represented in this forum, which ones start the week with Sunday, and which start it with Monday (or the equivalents in the local language)? Does anyone know when European calendars switched to starting the week with Monday? Or why, for that matter? Was it just to emphasize that secular culture isn't bound by church rules? Regards,James

 Re: When does a calendar week start? (was: Day of Week & Days Between Dates - Lighter version)Message #27 Posted by Gerson W. Barbosa on 1 Oct 2005, 12:01 p.m.,in response to message #26 by James M. Prange (Michigan) Quote: I notice that you have Saturday=0 through Friday=6, but ISO 8601 defines the day of week numbers as Monday=1 through Saturday=7, presumably in accordance with European calendars starting the week on Monday. Here in the U.S.A., our calendars have stuck with the tradition of the week starting on Sunday I thought it was quite the contrary, because as least in two European languages, Portuguese and German, the week seems to start on Sunday. The word for Wednesday in German is Mittwoch, which means, I think, "middle of the week". If this is correct, then Wednesday is the fourth day of the week and therefore Sunday is the first day. In Portuguese, as I have already mentioned, the business days are ordinal numbers: segunda-feira, terça-feira, quarta-feira, quinta-feira and sexta-feira, litteraly "second fair", "third fair",... "sixth-fair" (fair = market place). I think this is because the medieval fairs that were held throughout the week, but I may be wrong (I have heard of another reason, but I don't remember what should it be). If European calendars now start the week on Monday, you may be right about the reasons. Soon after the French Revolution, for a while they even abandoned the Gregorian calendar. Regards, Gerson.

 Re: When does a calendar week start?Message #28 Posted by James M. Prange (Michigan) on 2 Oct 2005, 1:50 a.m.,in response to message #27 by Gerson W. Barbosa Note that language doesn't always stay in synch with the calendar. For example, our English September, October, November, and December have roots in the Latin for seven, eight, nine, and ten, even though March hasn't been the first month for quite some time. Regards,James Edited: 2 Oct 2005, 2:15 a.m.

 Re: When does a calendar week start? (was: Day of Week & Days Between Dates - Lighter version)Message #29 Posted by Christoph Giesselink on 5 Oct 2005, 3:26 p.m.,in response to message #27 by Gerson W. Barbosa Quote: I thought it was quite the contrary, because as least in two European languages, Portuguese and German, the week seems to start on Sunday. The word for Wednesday in German is Mittwoch, which means, I think, "middle of the week". If this is correct, then Wednesday is the fourth day of the week and therefore Sunday is the first day. Before 1976 in Germany Sunday was the first day of the week, since 1976 Monday is the first day according to DIN 1355 (for those who understand German http://de.wikipedia.org/wiki/Woche). About a later question if calendar weeks are used, I can definitely say "Yes" for Germany. Mostly every working dead line is given as calendar week. In practise this means, when the dead line is for example KW39 (German for Kalenderwoche 39, 09/26/05-10/02/05) you should have it on Monday KW40. ;-) Finally I want to point to my date conversation routines for the HP-42S which can be found at http://www.hp42s.com/programs/date/date.html working with every date of the Gregorian calendar (October 15/1582 to December 31/9999). Technical notes about implementation can be found at http://www.hp42s.com/programs/date/olddate.html. Regards, Christoph, Germany

 Re: When does a calendar week start? (was: Day of Week & Days Between Dates - Lighter version)Message #30 Posted by James M. Prange (Michigan) on 7 Oct 2005, 7:44 a.m.,in response to message #29 by Christoph Giesselink Thank you! I was very curious as to when the week changed from starting with Sunday to starting with Monday for part of the world. Does anyone know of a country that changed earlier? But really now, a DIN was published and everyone changed their calendars just because of that? Okay, I realize that it's an ISO standard and ANSI (American National Standards Institute) is a member, but I wouldn't expect our calendars to change in the foreseeable future. Even (or perhaps especially) if the government were to recommend the change, Americans often tend to stick with tradition. For example, our packages for most consumer products usually have SI units on them where applicable, but rarely lack showing the "customary" units as well. "Weekly planning" pages in business "planners" start with Monday with small entries at the end for Saturday and Sunday, (a bit annoying for most of us) but the full-month and full-year calendars in them start the week with Sunday. But the planners do show the ISO 8601 week number on the weekly and daily pages, as well as the day of year and days remaining in year on the daily pages. I suppose they'd be useful if one were ever dealing with someone who used them, but the general consensus around here seems to be that the week numbers don't make any sense at all, so they're simply ignored. "KW40" is just fine for use within German-speaking countries, but even if you find an American familiar with ISO week dates, he's not likely to recognize that as meaning a week of the year. Of course an American would understand 10/02/05 or 10-02-05 as meaning October 2nd, 2005 without a second thought, and if even slightly acquainted with German notation, would understand 02.10.05 to be the same date. But written as 02/10/05, 02-10-05, 10.02.05, or 05-10-02, it's probably going to be misinterpreted over here. Personally, I prefer 2005-10-02, particularly for international use, or else October 2nd, 2005. Of course printed forms often indicate that the date should be in MM/DD/YYYY notation. I doubt that ISO week dates will catch on in the U.S., except perhaps for very limited uses. First there's the oddity of the week starting with the "wrong" day, and the days being numbered "wrong". Worse, the first week of the year may lack up to the first 3 days of the year, or may include up to the last 3 days of the previous year, and correspondingly, the last week of the year may include up to the first 3 days of the next year, or lack up to the last 3 days of the year. Okay, for purposes of comparing statistics for the weeks among years, I don't see any way to avoid such problems, at least not without causing even worse problems. But it's difficult for me to imagine ever using such a system for scheduling purposes or recording events. Regards,James

 Re: When does a calendar week start? (was: Day of Week & Days Between Dates - Lighter version)Message #31 Posted by valentino ducati (switzerland) on 11 Oct 2005, 5:33 p.m.,in response to message #30 by James M. Prange (Michigan) Quote:@James : : : "Weekly planning" pages in business "planners" start with Monday with small entries at the end for Saturday and Sunday, (a bit annoying for most of us) but the full-month and full-year calendars in them start the week with Sunday. But the planners do show the ISO 8601 week number on the weekly and daily pages, as well as the day of year and days remaining in year on the daily pages. I suppose they'd be useful if one were ever dealing with someone who used them, but the general consensus around here seems to be that the week numbers don't make any sense at all, so they're simply ignored. "KW40" is just fine for use within German-speaking countries, but even if you find an American familiar with ISO week dates, he's not likely to recognize that as meaning a week of the year. : : I doubt that ISO week dates will catch on in the U.S., except perhaps for very limited uses. : : : Hi James That's funny, we all here are aficionados of artefacts that really does catch with week days: our hp calculators. Have a look at the serial number coding that hp uses for the calculators. Here they are - in a big U.S. company. The calendar weeks you call obsolete... :-D Valentino

 Re: When does a calendar week start?Message #32 Posted by James M. Prange (Michigan) on 12 Oct 2005, 3:26 a.m.,in response to message #31 by valentino ducati (switzerland) First off, the use of a calendar week number in HP serials would be an example of "very limited use". And yes, I was well aware of it. I wonder, does HP's week numbering system follow ISO 8601? There are quite a few other ways one could number the weeks in a year. I never called it "obsolete", just of limited usefulness. Regards,James Edited: 12 Oct 2005, 6:06 a.m.

 Carnival and Easter Days on the HP-42S - no listing! (Re: When does a calendar week start?) Message #33 Posted by Gerson W. Barbosa on 7 Oct 2005, 1:11 p.m.,in response to message #29 by Christoph Giesselink Quote: Finally I want to point to my date conversation routines for the HP-42S which can be found at http://www.hp42s.com/programs/date/date.html working with every date of the Gregorian calendar (October 15/1582 to December 31/9999) Very interesting routines! There's even one for calculating the day of the Easter! About twelve years ago a wrote a 42S program for doing this. No, not for religious purposes, just for planning my vacations. I had to choose my vacations at least six months in advance, and I wouldn't want them to coincide either with Carnival or Easter, since here they are a five-day holiday anyway :-) By what I can remember, the program is based on a formula by Euler (I simply ported a BASIC program that was published in a local scientific magazine to the HP-42S). It works for any year in the range from 1900 to 2099 (enough for what I had in mind). For example, given 2005 the output will be: ```Carnival: Feb-06-2005 Easter: Mar-27-2005 ``` The program (361 bytes long) is far from being of general interest. Anyway, I can provide a .RAW file for Emu42 (Thanks, Christoph!) if anyone is interested. Regards, Gerson. Edited: 7 Oct 2005, 1:18 p.m.

 Re: When does a calendar week start? (was: Day of Week & Days Between Dates - Lighter version)Message #34 Posted by Gunnar Degnbol on 2 Oct 2005, 4:42 a.m.,in response to message #26 by James M. Prange (Michigan) Quote: Does anyone know when European calendars switched to starting the week with Monday? Or why, for that matter? Was it just to emphasize that secular culture isn't bound by church rules? I did some googling. It turns out the reason is theological: 1) The third commandment says: Remember thou keep holy the Sabbath day 2) The Christian Sabbath is Sunday 3) The Sabbath is the seventh day Therefore, Monday is the first day of the week. QED. Here are some links: The Days of the Week. Lots of information about weekdays names in different languages, and this: Quote: The convention, becoming more common, to start calendar weeks on Monday, is a result of the Western European names, especially the German ones, which do not call Saturday the Sabbath -- or do not do so anymore in a recognizable way. Since Christians, especially Protestants, think of Sunday as the "Sabbath," the tendency is to number it as the 7th, rather than as the 1st, day. Familiarity with Greek or Arabic, or several Romance languages, however, would inform one that Saturday remained the Sabbath, as in Hebrew, even for Christians and Muslims. Quote: In ancient Jewish tradition Saturday is the sabbath. Many languages lack separate words for "Saturday" and "sabbath". Eastern Orthodox churches distinguish between the sabbath (Saturday) and the Lord's day (Sunday). Roman Catholics put so little emphasis on that distinction that many among them follow — at least in colloquial language — the Protestant practice of calling Sunday the sabbath. Sunday is NOT the Sabbath!. This page explains why real protestants keep Saturday holy: Quote: So which authority do you acknowledge, the Word of God that commands seventh day Sabbath worship or the Tradition of the Catholic Church which commands Sunday, first day worship? There is no other choice.

 Re: When does a calendar week start?Message #35 Posted by James M. Prange (Michigan) on 2 Oct 2005, 8:35 a.m.,in response to message #34 by Gunnar Degnbol Granted, the Jewish may use "Remember the Sabbath Day to keep it holy." My understanding is that the Hebrew names for the first six days of the week mean simply first through sixth, and that "Sabbath" comes from the Hebrew word for "rest", not "seventh". Since the Old Testament tells us that God rested on the seventh day, the Jews (and some Christians) quite naturally observe their day of rest (their Sabbath) on the seventh day of the week; surely God's example should be a good thing to follow. Since the word "remember" is used in the commandment, I surmise that it was an established tradition that was sometimes forgotten or ignored. Note that the seven-day week wasn't restricted to Jews in pre-Christian times; at least the Romans used it. Where and when it started and how widely it was used, I don't know; I suppose that the obvious answer for "where" would be in the Garden of Eden, and for "when" would be when God rested after Creation. If I recall correctly, my catechism said "Remember to keep holy the Lord's Day." Anyway, keep in mind that these commandments are abbreviated (and translated, or perhaps mistranslated) forms of the full text of the Old Testament. Note that Christians generally consider the New Testament as superceding the Old Testament, so old rules could be replaced by new rules. From my reading of the Bible, it seems to me that God changed his policies quite a few times; for anyone who believes that Christ was God incarnate, surely Christ's authority overrides anything in the Old Testament. As the New Testament tells us that Christ's resurrection as well as the Holy Ghost's descent occurred on Sunday, many Christians (particularly Roman Catholics and most Protestants) consider Sunday to be the "Lord's Day", and thus the day of rest (the Sabbath). Surely many early Christians preferred not to honor the Jewish holy day. That doesn't mean that the first day of the week suddenly became the seventh day of the week, but rather that the holy (and rest, or Sabbath) day changed from the seventh day to the first day (for these Christians). As far as I can determine, the traditional seven-day cycle of the week was unbroken for thousands of years, although of course various cultures used various names for the days of the week, and (many) Christians changed the day of rest from the seventh day to the first day, and for that matter, Muslims changed it to the sixth day, but with Sunday (or the equivalent in the various languages) still considered to be the first day of the week. As far as I can figure out, starting the week on Monday seems to be a relatively recent (20th century?) European innovation. Anyway, in the U.S.A., calendars still show the week as starting on Sunday. Although in "planners" (such as Franklins), intended primarily for business use, "weekly" pages start with Monday, with smaller entries at the end for Saturday and Sunday, and both the "daily" and "weekly" pages show the ISO 8601 week of year number. That said, even in a Franklin planner, full monthly and yearly calendars show the week as starting on Sunday, and of course, the ISO 8601 week of year and day of week isn't often (ever?) used in the U.S.A. So where does the week start on your calendar? For that matter, do you ever use the ISO 8601 week of year and day of week numbers? By the way, I'm trying to avoid starting any religious-based flame war here; I'm not saying that any particular religion is right or wrong. Still, religions have certainly influenced history, particularly the history of calendars. Regards,James Edited: 2 Oct 2005, 8:44 a.m.

 Re: When does a calendar week start?Message #36 Posted by Gunnar Degnbol on 2 Oct 2005, 10:23 a.m.,in response to message #35 by James M. Prange (Michigan) Quote: As far as I can figure out, starting the week on Monday seems to be a relatively recent (20th century?) European innovation I think that if the reason really was to make Sunday the seventh day of the week to make it fit the Bible, then it sounds more like a 18th or 19th century thing, at the latest. Few 20th century Europeans would bother. Quote: So where does the week start on your calendar? The week always starts on Monday here. Software that does not allow configuration of the start of the week is broken. Quote: For that matter, do you ever use the ISO 8601 week of year and day of week numbers? ISO 8601 Week numbers are used a lot, for holiday planning and anything that references a specific week. There is not much reason to number the days in a week (except internally in software), they have names. My Nokia supports weeks starting on Saturday, Sunday or Monday, and shows ISO week numbers if it starts on Sunday or Monday. Quote: By the way, I'm trying to avoid starting any religious-based flame war here; I'm not saying that any particular religion is right or wrong. No, that was my worry after I posted :-) Quote: Still, religions have certainly influenced history, particularly the history of calendars. Yes, it is very interesting to discover the logic, to the extent there is any, behind the things we take for granted. It is very often based in religion.

 Re: When does a calendar week start? (was: Day of Week & Days Between Dates - Lighter version)Message #37 Posted by Arnaud Amiel on 3 Oct 2005, 2:01 p.m.,in response to message #26 by James M. Prange (Michigan) In Chinese, Monday is "Week 1" Tuesday "Week 2" etc until sunday which is "Week Day" Also, the name of months is easy January "1 Month" up to "12 Month" Arnaud

 Re: When does a calendar week start? (was: Day of Week & Days Between Dates - Lighter version)Message #38 Posted by James M. Prange (Michigan) on 6 Oct 2005, 6:00 p.m.,in response to message #37 by Arnaud Amiel So it seems that they start the week with Monday in China, surely a large proportion of the world's populataion. How about in the U.K.? Regards,James

 Re: Watch out for Y2KMessage #39 Posted by Howard Owen on 30 Sept 2005, 11:02 p.m.,in response to message #23 by Palmer O. Hanson, Jr. Must be a part of the algorithm I'm unfamiliar with. Why wouldn't 4000 be a leap year, since it's divisible by 400?

 Re: Watch out for Y2KMessage #40 Posted by James M. Prange (Michigan) on 1 Oct 2005, 12:58 a.m.,in response to message #39 by Howard Owen In the Gregorian calendar, a year divisible by 4 is a leap year, unless it's also divisable by 100, in which case it's not a leap year, unless it's also divisible by 400, in which case it's a leap year after all. Regards,James

 Re: Watch out for Y2KMessage #41 Posted by Howard Owen on 1 Oct 2005, 1:16 a.m.,in response to message #40 by James M. Prange (Michigan) Yes.

 Re: Watch out for Y2KMessage #42 Posted by James M. Prange (Michigan) on 1 Oct 2005, 2:41 a.m.,in response to message #41 by Howard Owen Sorry Howard, I guess that I got mixed up as to whom I meant to reply to. By the way, I strongly suspect that what Palmer had in mind was a proposed additional rule, suggested by the famous astronomer John Herschel, that years divisible by 4000 not be leap years. This would change the average calendar year length from 365 97/400 days to 365 969/4000 days, and would be closer to the observed length of a tropical year, although still a trifle long. However, as far as I know, no church, government, or standards organization has ever officially adopted this rule; it's certainly not part of the Gregorian calendar. Of course, with the leap seconds, years are (on average) slightly longer, and I suppose that leap seconds will be needed more frequently in the future, which would move the calendar even farther out of synchronization with the seasons, so maybe Herschel's proposed rule wouldn't be enough by the time the year 4000 gets here. But I've read that the U.S. has (unfortunately, IMO) proposed eliminating these adjustments to keep UTC in synch with astronomical time. I think dealing with the leap seconds is enough for now; changes to the calendar rules can be left for future generations to deal with. Regards,James

 Re: Watch out for Y2KMessage #43 Posted by Garth Wilson on 1 Oct 2005, 4:29 a.m.,in response to message #42 by James M. Prange (Michigan) Quote: This would change the average calendar year length from 365 97/400 days to 365 969/4000 days, According to HP, there are 365.242198781 days per year.

 Year length (was: Watch out for Y2K)Message #44 Posted by James M. Prange (Michigan) on 1 Oct 2005, 5:47 a.m.,in response to message #43 by Garth Wilson Actually, at least in the 48/49 series, the units base for 1 year is 31556925.9747 seconds, but I don't know where they got that value from. Of course they equate 1 day to 86400 seconds, so they don't attempt to take leap seconds into account. So yes, 1_yr converts to 365.242198781_d in these calculators. Anyway, a Gregorian calendar year, averaged over the 400 year cycle, is 365.2425 days. With Herschel's proposed change, averaged over the resulting 4000 year cycle, it would be 365.24225 days; still a little long. Of course the Greek Orthodox calendar uses a different set of rules for exceptions to having a leap year every 4th year, which brings them a bit closer to the observed tropical year. Regards,James Edited: 1 Oct 2005, 5:50 a.m.

 Re: Year length (was: Watch out for Y2K)Message #45 Posted by John Limpert on 3 Oct 2005, 1:49 p.m.,in response to message #44 by James M. Prange (Michigan) That long number (31556925.9747) is from the definition of the ephemeris second as the fraction 1/31556925.9747 of the tropical year for 1900 January 0 at 12h ephemeris time.

 Re: Watch out for Y2KMessage #46 Posted by Palmer O. Hanson, Jr. on 1 Oct 2005, 9:47 p.m.,in response to message #42 by James M. Prange (Michigan) I was relying on the following quotation from page 619 of Volume 4 of the 1969 version of Encyclopedia Britannica: "... Later, a slight change was made in the Gregorian calendar to bring it still more closely into line with the tropical year. The Gregorian calendar was still in error by one day in 3,323 years and, in consequence, a further rule of intercalation has been adopted that makes the year 4000, 8000, etc., common years, i.e., years without an intercalated day. The calendar is now, therefore, correct to within one day in 20,000 years. ..."

 Leap year rules (was: Watch out for Y2K)Message #47 Posted by James M. Prange (Michigan) on 2 Oct 2005, 12:50 a.m.,in response to message #46 by Palmer O. Hanson, Jr. I'm surprised. At least ISO 8601:2000 section 4.3.2.1 includes: "The Gregorian calendar distinguishes common years with a duration of 365 calendar days and leap years with a duration of 366 calendar days. A leap year is a year whose year number is divisible by four an integral number of times. However, centennial years are not leap years unless they are divisible by four hundred an integral number of times." Could it be that the Encyclopedia Britannica is mistaken? That said, I haven't seen a copy of ISO 8601:2004, and don't feel like paying \$101 for a copy of it. Regards,James

 Re: Leap year rulesMessage #48 Posted by James M. Prange (Michigan) on 2 Oct 2005, 1:34 a.m.,in response to message #47 by James M. Prange (Michigan) PS: With an error of one day in 3,323 years, the proposal to drop leap years every 3200 years seems to make more sense. See: http://mindprod.com/jgloss/leapyear.html. Of course, I don't see calendar reform as being particularly urgent. Regards,James

 Re: Leap year rulesMessage #49 Posted by Howard Owen on 2 Oct 2005, 2:14 a.m.,in response to message #48 by James M. Prange (Michigan) This is all very interesting and enlightening. I've learned a whole lot more about calendars than I knew before this thread. One thing I did know was that leap-seconds aren't added for the purpose of correcting for the base error in the calendar the way additional leap-year days are. They are there to compensate for the slowing of Earth's rotation, and consequent lengthening of the day. But what makes us look for an even multiple of 100 to correct an error whose period is 3,323 years? In other words, why not make the year 3323 a leap year, instead of 4000 or even 3200? Edited: 2 Oct 2005, 2:15 a.m.

 Re: Leap year rulesMessage #50 Posted by James M. Prange (Michigan) on 2 Oct 2005, 5:02 a.m.,in response to message #49 by Howard Owen Yes, seconds are added (or dropped, though that hasn't occurred) to keep the clock very nearly in synch with Earth's varying rotation, not to keep the calendar in synch with the seasons. However, a leap second does have the additional effect of lengthening the year, thus having a small effect on the discrepancy between the calendar and the seasons. After all, 86400 leap seconds would have the same effect on this as one extra leap year. How many years will it take for 86400 leap seconds to accumulate? I don't know; I haven't researched that, but since tidal forces are slowing Earth's rotation, it seems reasonable to expect that leap seconds will be needed more frequently in the future. Unless, of course, we actually do stop using leap seconds and just allow astronomical time to drift farther and farther out of synch with clock time. As for looking for an integer multiple of 100 instead of simply using multiples of 3323 to make additional corrections to the calendar, we'd want to (in addition to our current rules) drop a leap year around that time, not add one, so it would at least have to be a year that would be a leap year by the other rules. Clearly, the year 3323 is out; how about years that are integer multiple of 3324? At first, that seems to work, but how about the year 83100 (25*3324)? That wouldn't be a leap year by the current rules. Even just a multiple of 100 wouldn't suffice, as 3 out of 4 multiples of 100 aren't leap years by current rules. It seems to me that it would be best to use years that are multiples of 400 (always leap years by current rules), such as 3200 or 4000, for any additional rule. Of course, by the year 83100 (or even 3323, for that matter), who knows what kind of clock and calendar systems they'll be using? Will they remember an extra rule? (Recall the questions of whether the year 2000 would be a leap year.) How many leap seconds will have accumulated by then? Will they still be using a decimal number system, or will they have changed to, say, an octal or hexadecimal system for everyday counting by then? Will they feel bound by "the dead hand of the past"? Maybe we'll just wait until the discrepancy between the calendar and the seasons is (averaged over a 400 year cycle) a whole day and then drop a leap year. By the way, the Gregorian leap year rules are intended to keep the vernal equinox on or near March 21st, as it was at the time of the First Council of Nicea (A.D. 325), which determined that March 21st (regardless of the actual equinox) should be treated as the vernal equinox for Easter calculations, which explains Pope Gregory XIII's interest in the matter. More information on this can be found at http://www.newadvent.org/cathen/03168a.htm. Of course, even though the calendar reform was for ecclesiastical purposes, keeping the calendar in synch with the seasons also serves a secular purpose. Regards,James

 Re: Leap year rulesMessage #51 Posted by Walter B on 2 Oct 2005, 9:05 a.m.,in response to message #50 by James M. Prange (Michigan) Ok, folks, let's strive to reach the year 3323 at all! Remember oil will be exhausted within the next 50 years. And there is the greenhouse effect leading to some more severe hurricanes and similar stuff. Oh sorry, I forgot, according to the present administration there is no greenhouse effect! So there is a good (?) chance a well known superpower will start a war on this with the result there is no need for long range calendar corrections anymore. Good luck! ((;-)

 Re: Leap year rulesMessage #52 Posted by James M. Prange (Michigan) on 2 Oct 2005, 9:40 a.m.,in response to message #51 by Walter B Hey, I'm pretty certain that I, personally, won't reach the year 3323. Yes, there are certainly plenty of problems far more urgent than additional leap year reform to be solved. I think we can leave that issue for (hoped-for) generations far in the future to address. Of course, I do rather wish that the silly ISO 8601 week of year numbers would be dropped; since a Gregorian calendar year never has an integer multiple of 7 days in it, there doesn't seem to be any good way to number the weeks of the year. And since there seems to be very little chance that those cultures that start the week with Sunday will ever use the ISO day of week numbers starting with Monday as 1, they seem much more likely to cause confusion than to standardize usage Regrds,James

 Re: Leap year rulesMessage #53 Posted by don wallace on 2 Oct 2005, 2:50 p.m.,in response to message #51 by Walter B Hi all. Interesting thread. NOTE: The following IS kinda o.t.: (but provided as a community service announcement of sorts) Actually the permanent oil crisis is here now. Although many still aren't too aware (state of denial) and figures in the tens of years (50,100) are often seen, the data are scary, much closer than 50 years. The (fatal?) impacts will probably arrive in an irreversible form within TEN years, maybe FIVE. Consider that running out of oil is not the problem, but the END OF CHEAP OIL is. See www.aspo.org Maybe someone might like to do a quick simulation (on an hp calc of course) to predict economic collapse from incremental rise in oil prices (with resulting flow on effects into EVERY COMMODITY REQUIRING TRANSPORT). The modern economy is in fact very fragile and Bush and Cheney know it. So does John Howard and Tony Blair. Of course, one (tried and tested) way to avoid collapse is to steal assetts / resources from other countries under a pretext. That action only staves off the end, of course. I saw a documentary called: End of Suburbia and can recommend it. Of course I have read extensively on this problem (only since april 2004). I am amazed how complacent most people still are about this problem. All the best for the future everyone. Don W Edited: 2 Oct 2005, 2:51 p.m.

 Re: Leap year rulesMessage #54 Posted by Gerson W. Barbosa on 2 Oct 2005, 10:55 p.m.,in response to message #50 by James M. Prange (Michigan) Quote: Of course, even though the calendar reform was for ecclesiastical purposes, keeping the calendar in synch with the seasons also serves a secular purpose. In order to achieve this, shouldn't we also compensate for the effect of the precession of the equinoxes on the dates seasons begin? Any ideas? Regards, Gerson.

 Re: Leap year rulesMessage #55 Posted by James M. Prange (Michigan) on 4 Oct 2005, 6:17 p.m.,in response to message #54 by Gerson W. Barbosa Quote: Quote: Of course, even though the calendar reform was for ecclesiastical purposes, keeping the calendar in synch with the seasons also serves a secular purpose. In order to achieve this, shouldn't we also compensate for the effect of the precession of the equinoxes on the dates seasons begin? Any ideas? I think that if we were using a sidereal (star-based) calendar year, based on something like keeping the rising of a particular star near the ecliptic at a certain time on a particular day of the year, you'd have a very good point. But in fact the Gregorian calendar is designed to keep the observed vernal equinoxes, on average, near March 21st, so everything that's affected the timing of the vernal equinox is already included, to the extent that the vernal equinox actually does (on average) stay near March 21st. Regards,James

 Re: Watch out for Y2KMessage #56 Posted by Gerson W. Barbosa on 2 Oct 2005, 1:00 p.m.,in response to message #46 by Palmer O. Hanson, Jr. Perhaps neither TI nor HP expected their products to last until the year 4000 A.C. :-) Though the calendar is now that accurate, you'll be celebrating Christmas in the Summer, like we do down here, by the year 15,000 A.C. ... Will this be a problem? Besides your post being enlighting, it helped me spot a mistake in my listing that would prevent the program to work correctly for some years ending in 00. (My hand-written listing on the Master Library was ok though). Thanks. Edited: 2 Oct 2005, 1:03 p.m.

 Re: Watch out for Y2KMessage #57 Posted by valentino ducati (switzerland) on 3 Oct 2005, 5:51 p.m.,in response to message #56 by Gerson W. Barbosa Quote: Perhaps neither TI nor HP expected their products to last until the year 4000 A.C. :-) But, apart from battery problems and capacitors drying: Is the "plastic" body of a classic, woodstock, voyager, pioneer or 41/48/49 still all right in a few 100 years? Or even thousands? And what about the metal parts of the older calculators? And the platin and chips on it? How long could they last? Anyone here with that material knowledge?

 Re: Watch out for Y2KMessage #58 Posted by John Limpert on 3 Oct 2005, 10:28 p.m.,in response to message #57 by valentino ducati (switzerland) Assuming they are used, the ICs will eventually fail from electromigration of the metal layer. The time period depends on feature size and current density.

 Re: Watch out for Y2KMessage #59 Posted by Palmer O. Hanson, Jr. on 3 Oct 2005, 10:58 p.m.,in response to message #57 by valentino ducati (switzerland) My guess is that plastic cases will become a problem. Some plastics become brittle with age. One of the prized items in my collection was a Speedee Add-a-matic (see the section of the museum on old calculators). Last spring I inadvertently knocked it off a table onto a terrazo floor. The plastic case shattered into about twenty pieces. The metal mechanism still works. By comparison back in the early 1980's I inadvertently knocked my almost new Radio Shack Model 100 off the same table onto the same terrazo floor. There was a small crack in one corner of the case. Some of the keys came off and the batteries came out of the compartment. I put the batteries back in, pressed the keys back in place and the machine was able to complete the calculations that were in process. That machine still works today. A "shock test" which illustrates how sturdy some of the hand-helds are when they are relatively new is the test of the oscillator described in the service manual for the TI-59. I'm not going to repeat that test today. Sorry about that! Who's going to do a drop test on his HP-35? I do have some old Sharps, Casios, and a number of spare TI-30's at my winter home. When I'm back there I just may have to do some drop tests. I also have three of the Addometers (again, see the old calculator section) which were all metal and made by a typewrter manufacturer back in the 1920's. Two of the three work well. The third is somewhat rusty and the dials only turn with some difficulty. A bad choice of metal can be a problem. The early Pickett slide rules used a magnesium alloy (I think) base. They often didn't move smoothly even when new but that problem can be solved these days with a little WD-40. Many of those now have the slide and frame fused together by corrosion. The late aluminum base devices have fewer problems.

 Re: Watch out for Y2KMessage #60 Posted by Dave Shaffer on 3 Oct 2005, 7:53 p.m.,in response to message #56 by Gerson W. Barbosa "Though the calendar is now that accurate, you'll be celebrating Christmas in the Summer, like we do down here, by the year 15,000 A.C. ... Will this be a problem?" Nope! It is, in fact, precisely the addition of leap years which KEEPS the seasons where they belong, due to the precession of the equinox. Us northerners will still have spring starting (about) March 21 and Christmas will still be in the winter. What will happen in 13000 years (half of a precession cycle) is that the stars which you now think of as "winter" stars (again, for us northerners; perhaps better stated as "December" stars) will be instead the summer/June stars. i.e. the constellation Orion will be prominent on June/July evenings in the year 15000, rather then the December/January evenings when we see him now. Another minor effect will be due to the ellipticity of the Earth's orbit. At this time, the Earth is closest to the Sun in early January. The effect on incoming solar energy is only a few percent, but this means that northern hemisphere winters are now somewhat warmer than they will be in 13000 years, when winter will be occuring when the Earth is farthest from the sun. Leap seconds (or the alternative now being touted by some folks at the US Naval Observatory - officially charged with keeping track of time for the United States - of changing the rate of atomic time by about 20 parts per billion) keep the rotational position of the Earth aligned with the stars. I have to think a bit about whether the accumulated leap seconds affect leap years. The Earth is not only slowing down overall, but at the level of 10's of microseconds per day speeds up and slows down - somewhat at random but also with seasonal variations that basically relate to the fact that there is more land mass in the northern hemisphere than in the southern hemisphere. This stuff is all very critical for very accurate (sub-centimeter) global geodesy. For more details on precise earth orientation and timekeeping, go to http://maia.usno.navy.mil .

 Re: Watch out for Y2KMessage #61 Posted by Gerson W. Barbosa on 3 Oct 2005, 10:50 p.m.,in response to message #60 by Dave Shaffer Quote: Nope! It is, in fact, precisely the addition of leap years which KEEPS the seasons where they belong, due to the precession of the equinox. Us northerners will still have spring starting (about) March 21 and Christmas will still be in the winter. I always thought the addition of leap years keeps the seasons in place because this makes the year closer to its actual length. But the seasons shifts due to the precession of the equinoxes would not be corrected by this method. Have I misunterstood anything? Here is an excerpt of Isaac Asimos's "A choice of catastrophes": "... In 12890 years, the [Earth's] axis shall turn to the opposite direction... ...and the Summers's Solstice [in the northern hemisphere] will be on December 21, and the Winter's Solstice on June 21..." (This is a bad translation back to English. The actual text should be somewhat different, but hopefully I may have kept the right meaning).

 (deleted post)Message #62 Posted by deleted on 4 Oct 2005, 12:11 a.m.,in response to message #60 by Dave Shaffer This Message was deleted. This empty message preserves the threading when a post with followup(s) is deleted. If all followups have been removed, the original poster may delete this post again to make this placeholder disappear.

 Re: Watch out for Y2KMessage #63 Posted by Dave Shaffer on 4 Oct 2005, 12:49 a.m.,in response to message #62 by deleted Don, Precession can be viewed as the "sliding" of the celestial reference frame (right ascension and declination - "RA/Dec" in astronomer shorthand) which is tied to the Earth (basically projection of latitude and longitude onto the sky) along the ecliptic (the more-or-less plane of the planetary orbits). If you think of the position of stars in an ecliptic coordinate system, they will not change with time. In the RA/Dec system, the star positions change continuously. So yes, the RA/Dec of Orion will change, but Orion will still be in the ecliptic, as will ALL the ecliptic constellations (so beloved of astrologers (gack, I HATE that word!). The path of the Sun, as viewed from the Earth, will continue to circle around the ecliptic once per year. Also, as I said earlier, leap years REALLY DO take care of the sliding of the seasons. The reason calendar reform was necessary was because the date March 21 was clearly no longer coinciding with the "beginning" of spring (defined as the day of the year on which the declination of the Sun is ZERO (i.e. the Sun was exactly on the celestial equator = Declination of the Sun is 0 degrees)). What was the problem: the length of the year was too short (as noted elsewhere in this discussion) if only 365 days were alloted to a year. So, leap years merely adjust the length of the year to match the actual time that the Earth takes to go around the Sun - with year here defined as the length of time from the beginning of one spring to the next spring. That's what our current calendar is based on - the spring-to-spring year. If the date of the seasons was going to switch, we would have already seen the effect. This problem has been known, more or less, for several thousand years. That would be enough to switch the beginning of spring by a month (i.e. around a twelfth of the 26000 year precession period) - which has not happened. So, (as long as we stick to the current calendar or some close approximation) Spring will continue to occur on March 21 for the forseeable future. In particular, for the next 13000 years. For more on this, try http://www-istp.gsfc.nasa.gov/stargaze/Sprecess.htm

 Re: Watch out for Y2KMessage #64 Posted by Gerson W. Barbosa on 4 Oct 2005, 11:26 a.m.,in response to message #63 by Dave Shaffer Quote: If the date of the seasons was going to switch, we would have already seen the effect. This problem has been known, more or less, for several thousand years. That would be enough to switch the beginning of spring by a month (i.e. around a twelfth of the 26000 year precession period) - which has not happened. Now you have convinced me! Thanks! Ne sutor ultra crepidam. From now on this shoemaker will stick just to heels, soles, shoelaces and the like :-)

 Re: Watch out for Y2KMessage #65 Posted by James M. Prange (Michigan) on 6 Oct 2005, 5:14 p.m.,in response to message #63 by Dave Shaffer My attempt to explain the "precession of the equinoxes", Milankovitch cycles, leap years... But I'm not anastronomer; I wouldn't even consider myself an "amateur astronomer" (I don't even have a telescope). But I do find astronomy, calendars, and time-keeping interesting. Maybe I'm an "armchair astronomer"? Anyway, take the following with a few grains of salt. First off, we have at least three major definitions of a year based on astronomy, in addition to the various calendar years. A "tropical" year, the period of the seasons. For example, from vernal equinox to vernal equinox; our Gregorian calendar year is based on this. A "sidereal" year, the period of the earth's revolution around the sun in relation to the "fixed stars", or equivalently, the apparent position of the sun against the starry background. Of course, the stars, galaxies, quasars, and so on are actually moving, but due to their immense distance from us, except for the nearest stars, any change in their apparent angular relationships as viewed from the earth is negligible. A sidereal year is about 20 minutes longer that a tropical year. Note that even the length of the sidereal year is changing, presumably due to transfers of angular momentum among the bodies of the solar system, "friction" with interplanetary gas and "dust", the affects of the solar wind, and so on. Everything in the universe affects everything else. An "anomalistic" year, the period from the earth's perihelion (closest approach to the sun in its elliptical orbit) to its next perihelion. An anomalistic year is about 25 minutes longer that a tropical year, or 5 minutes longer than a sidereal year. This precession is due (at least mostly) to perturbations of our orbit from the major planets, particularly Jupiter and Saturn. The period of this precession (in relation to the fixed stars) seems to be about 114000 years. The eccentricity (how nearly a true circle the orbit is) is thought to vary too, with a period of about 95000 years. The ecliptic is the plane of earth's orbit, so called because an eclipse of the sun or moon occurs when the moon crosses this plane very nearly at the new or full moon. Of course the sun, as viewed from the earth, always appears to be on the ecliptic. The constellations that appear to be on the ecliptic are called the zodiac. The sun, as viewed from the earth, appears to move through the zodiac once per sidereal year. As noted in another post, the ecliptic is very stable (at least in terms of human history), and except perhaps for some relatively nearby stars, so is the zodiac. Of course, when the sun evolves into a red giant, that will effect Earth's orbit, to put it mildly, but no one on Earth will be concerned with that. The moon's orbital plane around the earth is at an angle of about 5.1 degrees to the ecliptic. The orbital planes of the other planets, except Pluto, are near the ecliptic, ranging from about 0.8 degrees from the ecliptic for the orbital plane of Uranus to 7.0 degrees for Mercury's, so the planets also appear to be near the ecliptic. Even Pluto's orbital plane is only about 17.2 degrees from the ecliptic. The celestial equator is the earth's equator projected into the sky. Of course the plane of the celestial equator is perpendicular to the earth's axis of rotation. The celestial poles are the earth's axis of rotation projected into the sky. Currently, the north celestial pole is near Polaris (the North Star). Currently, the planes of the ecliptic and celestial equator are at an angle of about 23.5 degrees, though that's thought to vary a few degrees with a period of about 41000 years. An equinox occurs when the earth passes through the line of intersection of the planes of the ecliptic and the celestial equator. Because the earth spins, it has an equatorial bulge. The sun's and moon's gravity pull on this bulge, one might say trying to pull it into alignment with a line from the sun to the moon, in effect, applying a torque to the earth's rotational axis. As anyone who's played with a gyroscope should recognize, the affect is to cause a precession of the earth's axis, causing it to sweep out a (more or less) cone in the sky, relative to the fixed stars. This precession has a period of about 26000 years, relative to the fixed stars. One effect is that Polaris is near the axis only periodically; the stars (as viewed from the northern hemisphere) won't always appear to revolve around it. The celestial poles move in (more or less) circles in the sky. Since the plane of the celestial equator is perpendicular to the axis, as the axis precesses, this plane "wobbles" (for lack of a better term) in synch with it, and of course, this causes its line of intersection with the ecliptic plane to rotate one full turn for every period of the precession, and thus the equinoxes to move relative to the fixed stars, so the apparent position of the sun at the time of the vernal equinox moves through the zodiac once for every period of precession. Note that there are also smaller. faster, oscillations of the axis, known as nutations. As noted above, the point of perihelion is precessing, and the combined effect of this precession with the precession of the equinoxes in the opposite direction is that the period of Earth's perihelion coinciding with the vernal equinox is about 21000 years. Because the earth's orbital speed (like a comet's) is fastest at perihelion (currently about January 3rd) and slowest at aphelion (currently about July 5th) the length of the seasons vary too; currently shortest for (northern hemisphere) winter, with autumn longer, then spring, and summer longest. We all know that the sun appears to revolve around the earth due to the earth's rotation, but actually, the sun's apparent daily motion across the sky is a combination of both the earth's rotation and its revolution around the sun. After all, if the earth didn't rotate at all in relation to the fixed stars, the sun would appear to revolve around us once per sidereal year, in the direction opposite to what we're familiar with. As the earth is both closest to the sun and at its highest orbital speed at its perihelion, the sun's apparent motion from the earth's revolution around the sun would be fastest at perihelion. A sidereal day, the period of Earth's rotation relative to the fixed stars, is about 3 minutes 56 seconds shorter than a mean solar day. The earth really rotates, relative to the stars, about 366-1/4 times per year, but Earth's revolution around the sun makes the sun appear to revolve around the earth only about 365-1/4 times per year, that is, the earth's revolution around the sun slows down the apparent motion of the sun around the earth. Because the earth's orbital speed is fastest at perihelion, and the distance to the sun is shortest, the sun's overall apparent motion is slowest at perihelion, so a solar day (as from high noon to high noon) is longest near perihelion. No doubt Earth's actual orbit is much more complicated than I've mentioned, but I think that I've covered the most important points. The relationships of the above periodic motions are the bases of Milankovitch cycles, which may well have an affect on our climate, though they don't totally account for the apparent climatological record. To simplify timekeeping, we use a "mean solar day". Of course now we no longer define a second as 1/86400 mean solar day, but rather define a second by atomic clocks, and a day as 86400 seconds, adding (or potentially dropping) a second occasionally as needed to keep UTC close to astronomical time. As noted in another post, earth's rotation varies, and it's difficult to predict exactly how long a solar day will be. Before accurate timekeeping was available, a day was a solar day. Exactly how long was a solar day in Caesar's or Pope Gregory's time? At first glance, that would seem to be a good question for geophysicists, but maybe astronomers can have an important role in this. Because the earth's and moon's orbits are known, astronomers can determine when an eclipse occurred in the past. By looking at records of eclipses, some answers as to the exact date of some events can be found, even though various calendars were used. Astronomy can also tell us where a solar eclipse should have been visible from; comparing this with the historical record could give us information on the rotation of the earth. Of course, an astronomer may well respond "been there, done that". Regarding leap years, to be pedantic, they're used simply because a tropical year, rather inconveniently, doesn't happen to be a whole number of days long. Before Julius Caesar's reform, Roman years varied in length, typically with 355 days, with an extra month added to the year as needed to bring the calendar back close to the seasons. Sometimes, as in times of war, they neglected to add the extra month. Besides the rather irregular length of year, exactly when to add the extra month was subject to political/financial pressures, a rather unsatisfactory situation for many. Of course now we change the dates of the "fiscal year" instead, and Michigan's government is currently shifting the dates of its "property tax year". Of course, they're not increasing the taxes, they're just having the counties collect taxes earlier every year for the next few years. Yeah, right.... Anyway, a fixed-length year would be an obvious solution the Romans' problems with the calendar, but a 366-day calendar year is too long, and a 365-day calendar year is too short. Having a "partial day" in every calendar year would seem rather inconvenient. Julius Caesar's calendar reform came fairly close. The idea is to keep the average calendar year very nearly the same length as the average tropical year, while also keeping each calendar year a whole number of days long, and varying the length of the calendar year by only 1 day. Three calendar years of 365 days followed by one of 366 days, and repeating this cycle indefinitely, was an elegant solution. Unfortunately, with Julius Caesar already dead, his reform was apparently misunderstood to mean a leap year every three years, and this error was finally corrected by Caesar Augustus after 36 years. Of course it would've been more "elegant" to distribute the days of the months something like the following: ```Month normal year leap year number length length 1 30 30 2 31 31 3 30 30 4 31 31 5 30 30 6 31 31 7 30 30 8 31 31 9 30 30 10 31 31 11 30 30 12 30 31 ___ ___ total 365 366 ``` and for that matter, start both month #1 and the year on (okay, near) the day of the vernal equinox. Why the vernal equinox? Well, it's the beginning of spring, a season that seems to me symbolic of renewal (birds, bees, eggs, flowers, bunnies, etc.), and an equinox is fairly easily verifiable by rather simple astronomical observation, and thus a good time to start a new year. On the other hand, the solstices seem to me even more obvious (sunrise and sunset farthest south or north, sun at "high noon" farthest south or north relative to the zenith), so wouldn't be bad choices, although the changes in sunrise/sunset direction and the daily highest point of the sun are smallest near the solstices and greatest near the equinoxes. Of course the year has actually started on various dates in various cultures. But the Julian calendar was certainly a huge improvement from the previous Roman system. Besides, February is such a depressing month around here that I'm rather glad that it's the shortest of all. Notably, under the Julian calendar, the vernal equinox was considered to be on the 21st of March, regardless of the actual astronomical date, and for the purpose of calculating the date of Easter, it still is by most western Christian churches, even with the Gregorian calendar. By Pope Gregory's time, it was evident that the average calendar year was too long, with an all too noticeable accumulated error of about 10 days in the date of the vernal equinox. Rather than totally discarding the existing leap year rules and starting over, they chose to modify them, dropping 3 out of every 100 leap years. Of course they also dropped 10 calendar days, so 1582 had only 355 days, at least in the Vatican's reckoning. In my opinion, it might've been simpler to just acknowledge that the vernal equinox was actually on a different date, and settle for the leap year modifications to keep it from drifting much farther. Maybe it would've been easier to get the rest of the world to go along with this? But this still would've changed the date of Easter, giving the Protestant churches yet another reason to condemn the Pope. Of course other leap year rules, some arguably better, can be (and have been) devised, but for now, most of the world has adopted the Gregorian calendar, at least for most secular purposes. Regards,James

 Re: Watch out for Y2KMessage #66 Posted by James M. Prange (Michigan) on 7 Oct 2005, 8:17 a.m.,in response to message #65 by James M. Prange (Michigan) Quote: Of course they also dropped 10 calendar days, so 1582 had only 355 days, at least in the Vatican's reckoning. In my opinion, it might've been simpler to just acknowledge that the vernal equinox was actually on a different date, and settle for the leap year modifications to keep it from drifting much farther. But after thinking a little more, I realize that this would've been a big problem for the liturgical calendar. The entire Easter cycle could occur as much as ten days earlier, and without changing the timing of the Christmas cycle, the Easter cycle could begin before the "time after Epiphany" (the last part of the Christmas cycle) had even begun. No wonder they chose to keep the vernal equinox on March 21st. RegardsJames

 Re: Watch out for Y2KMessage #67 Posted by James M. Prange (Michigan) on 4 Oct 2005, 4:12 a.m.,in response to message #56 by Gerson W. Barbosa Quote: Perhaps neither TI nor HP expected their products to last until the year 4000 A.C. :-) "A.C."? Indeed, the valid "system time" on the 48/49 series covers only a 100-year range. For the 48SX/S, 1989-01-01 through 2088-12-31, and for the 48G series and 49 series, 1991-01-01 through 2090-12-31. Attempting to set a date outside of these ranges results in an "Invalid Date" error. Setting a date and time just before the maximum and letting it tick up to midnight results in a warmstart, with WSLOG showing a "System time is corrupt" entry, and for the 48 series and 49G, the system time jumps back 100 years, but strangely enough, my 49g+ jumps back only to 2003-01-01. Trying CLKADJ to try adjust it out of range either earlier or later jumps it to these same times, but without causing a warmstart. I find it interesting that they didn't move the range ahead a bit for the 49 series. Apparently it's an "artificial" restriction; with the 52-bit clock at 8192 ticks per second, they could've made the range far larger. It turns out that a binary system time (as from TICKS) of #0 would correspond to exactly time 00:00:00 on 0000-01-01 in a proleptic Gregorian calendar, and a binary system time of #FFFFFFFFFFFFF would be sometime in late January, 17421. Maybe they simply chose the range so that TSTR would only have to use 2 digits for the year? Similarly, the range of 1582-10-15 through 9999-12-31 for date arithmetic seems "artificial". It seems to me that, assuming a proleptic Gregorian calendar, the range could've been 0000-01-01 through 99999999-12-31. I'm not sure how much trouble it would've been to allow negative years, but if it were feasible at all, I suppose that they could've gone back to January 1st, -99999999. But I doubt that they expected the calculators to still be in use even in 2088. They may well be surprised that the older models, or even the 48SX/S, are still in use even today. But with the most recent models, I sometimes can't quite help suspecting that they designed in some planned obsolescence. Quote: Though the calendar is now that accurate, you'll be celebrating Christmas in the Summer, like we do down here, by the year 15,000 A.C. Well, barring some major medical breakthroughs and several other near miraculous circumstances, I won't be around here then. As others have pointed out, maybe it could be considered miraculous if humans weren't in a long "dark age" by then, if not extinct. Anyway, the way I figure, ignoring the effects of leap seconds, and assuming no adjustments other than the current Gregorian calendar rules were made, the seasons would occur only a bit less than 4 days earlier in the calendar year then, and I doubt that leap seconds would accumulate even a day's extra error in that time, so I suppose anyone living around here would be celebrating Christmas about 8 or 9 days after the winter solstice instead of about 4 days after it. Quote: ... Will this be a problem? I rather doubt that the few days drift would be a problem, unless accusations of heresy for not celebrating Easter at the proper time become fashionable again. Certainly it would be noticeable to astronomers, but I trust that they'd be able to deal with it. As for celebrating Christmas in the summer, at least they wouldn't have to put up with freezing rain, sleet, and snow while trying to do last-minute Christmas shopping, and the Christmas decoration lights wouldn't be on for so long, thus saving energy. But the kids would be trying out their new bicycles immediately, instead of their new sleds. Do Australians include artificial snowflakes, snowmen, and such in their Christmas decorations? Quote: Besides your post being enlighting, it helped me spot a mistake in my listing that would prevent the program to work correctly for some years ending in 00. (My hand-written listing on the Master Library was ok though). Thanks. Well, I'm glad that it helped. I confess that I didn't even attempt to follow the programs posted. The only "True RPN" model that I have is thr 16C that I inherited, and though I did work through the examples in the manual and try a few variations, I haven't tried programming it since. The 16C is wonderful for working with binary though. Regards,James Edited: 4 Oct 2005, 4:19 a.m.

 (deleted post)Message #68 Posted by deleted on 4 Oct 2005, 6:05 a.m.,in response to message #67 by James M. Prange (Michigan) This Message was deleted. This empty message preserves the threading when a post with followup(s) is deleted. If all followups have been removed, the original poster may delete this post again to make this placeholder disappear.

 Re: Watch out for Y2KMessage #69 Posted by James M. Prange (Michigan) on 4 Oct 2005, 8:47 a.m.,in response to message #68 by deleted Maybe your snowflakes and snowmen make it feel a little cooler? I suppose that many early "settlers" often wished they were back in Britain. Regarding the pagan origins for Christmas, St. Valentine's day, Easter (at least the eggs and bunny associations), All Saints' Day, Thanksgiving, etc., I suppose that telling the pagans to quit having their festivals would have been a dismal failure; much easier to change them to (more or less) Christian festivals. Around here, we really need something like Christmas to cheer us up around that time of year. Personally, I'd like a better celebration around Groundhog Day (February 2nd). The kids colour hard-boiled eggs before Easter, so they know where those came from. The usual story is that the Easter Bunny takes them out of the refrigerator and hides them various places around the house the night before Easter, but I don't think any of them actually believe that. They know full well that the Easter candy is from Gramma and Grandpa. Some organizations hold Easter egg hunts for large groups of children, with chocolate eggs hidden outdoors, but I don't think anyone believes any story that the Easter Bunny left them. Christmas is a different story though. I'm always amazed that most children actually do seem to believe in Santa Claus until they're about 7 years old. I don't remember ever believing in Santa Claus, any more than I believed in Donald Duck or Bugs Bunny. We did exchange presents of course, but no one pretended that Santa Claus was anything other than an amusing myth. Maybe my parents thought that Santa Claus was a bad idea for religious reasons, or maybe they thought that with with three older brothers and an older sister, I'd soon be told otherwise. I expect that their reasons were religious; Christmas and Easter always started with going to Mass, and the somewhat secular aspects were limited to a Christmas tree, lights, decorations, exchanging gifts on Christmas, and more elaborate dinners than usual, most of which had a religious explanation; these were very clearly "holy days" more than "holidays" in our home. Regards,James

 Re: Watch out for Y2KMessage #70 Posted by Gerson W. Barbosa on 4 Oct 2005, 9:50 p.m.,in response to message #67 by James M. Prange (Michigan) Quote: "A.C."? I should have said AD (Anno Domini). As I know you use the abbreviation BC (Before Christ), I wrongly guessed you'd use also use AC (After Christ) as we do here. About the dramatic seasons shifting as a consequence of the precession of the equinoxes, I was wrong as Dave Shaffer pointed out. By what I can see, contrary to what I thought, we are doomed to celebrating Christmas in the Summer for ever, a problem only for thousands of southern Santas that have work in Winter clothings under a tropical sun :-) Regards, Gerson.

 Re: Watch out for Y2KMessage #71 Posted by James M. Prange (Michigan) on 6 Oct 2005, 1:57 a.m.,in response to message #70 by Gerson W. Barbosa A.C. (After Christ) is new to me, though I'm familiar with C.E. (Christian Era) and B.C.E. (Before Christian Era) for the proleptic Gregorian calendar. Incidentally, this is usually taken to have a year 0000, which is a leap year, so the same leap year rules apply for negative years. For the Julian calendar, which doesn't have a year 0, A.D. and B.C seem to be the rule, but of course these have also been used for the Gregorian calendar. I suppose that C.E. and B.C.E. might by applied to the julian calendar too. I guess for dates before all western cultures adopted the Gregorian calendar (around 1750?), it's best to be specific about which calendar is meant. For my niece's genealogical research, I think that "New Style" and "Old Style" dates have caused some apparent anomolies. Which date something occurred on depends on which calendar is used. Regards,James

 Common EraMessage #72 Posted by Eric Smith on 6 Oct 2005, 8:19 p.m.,in response to message #71 by James M. Prange (Michigan) More generally referred to in non-religious context as Common Era (CE) and Before Common Era (BCE). See the Wikipedia article on the Common Era.

 Re: Common EraMessage #73 Posted by James M. Prange (Michigan) on 7 Oct 2005, 3:47 a.m.,in response to message #72 by Eric Smith Okay, now that you mention it, I think I've also seen "Common Era", but the alternative of "Current Era" on that page makes more sense to me. But if they wanted to get references to Christ out of the date, why didn't they choose some other epoch than the birth of Christ? Using that epoch makes the connection to Christianity extremely obvious. And of course Gregory was a pope, so shouldn't we stop using the term "Gregorian calendar"? Perhaps ISO 8601 should change all occurences of "Gregorian calendar" to, for examples, "ISO calendar", "common calendar", or "current calendar"? Like it or not, Christianity has had a real influence on history, including the epoch for our calendar. Not that I feel that a calendar for secular purposes particularly should have religious references, but since it already does, I don't see any good reason to change that. Regards,James

 Re: Common EraMessage #74 Posted by John Limpert on 8 Oct 2005, 11:55 p.m.,in response to message #73 by James M. Prange (Michigan) The problem is that A.D. stands for Anno Domini, "Year of our Lord". For a huge number of people, Jesus isn't "our Lord".

 Re: Common EraMessage #75 Posted by James M. Prange (Michigan) on 9 Oct 2005, 12:37 a.m.,in response to message #74 by John Limpert Quote: The problem is that A.D. stands for Anno Domini, "Year of our Lord". For a huge number of people, Jesus isn't "our Lord". Yes, obviously, but few would seriously doubt that Jesus Christ was a very real historical person. Even those who might think that the New Testament were completely fictitious wouldn't dispute the historical reality of Christianity, hence my mistake that "C.E." stood for "Christian Era". After all, whoever came up with "C.E." and "B.C.E." didn't choose to base a calendar on a new epoch that had nothing to do with Christianity. Regards,James Edited: 9 Oct 2005, 1:14 a.m.

 Re: Common EraMessage #76 Posted by Eric Smith on 9 Oct 2005, 3:02 p.m.,in response to message #73 by James M. Prange (Michigan) Quote: But if they wanted to get references to Christ out of the date, why didn't they choose some other epoch than the birth of Christ? So that they wouldn't have to change the dates of everything. The epoch of the Gregorian calendar (and the Julian calendar) isn't really the birth of Christ anyhow; scholars seem to think that happened some time around 4 or 5 BCE.

 Re: Common EraMessage #77 Posted by James M. Prange (Michigan) on 12 Oct 2005, 4:42 a.m.,in response to message #76 by Eric Smith Quote: So that they wouldn't have to change the dates of everything. So it seems to me that they weren't really very serious about removing any religious references from the calendar. Obviously, "A.D." (Anno Domini, Year of the Lord), would seem very inappropriate to non-christians, but I don't see why anyone would object to, for example, "Christian Era". Quote: The epoch of the Gregorian calendar (and the Julian calendar) isn't really the birth of Christ anyhow; scholars seem to think that happened some time around 4 or 5 BCE. Yes, there's very good reason to believe that the birth of Jesus of Nazareth actually occurred a few years before our calendar would seem to indicate. However, the particular scholar (Dionysius Exiguus) whose work the epoch is based on, apparently believed that Jesus turned 1 year old in 754 A.U.C., so he established that as the year 1 A.D. How certain he was, I don't know. Regards,James

 Re: Watch out for Y2KMessage #78 Posted by blurdybloop on 5 Oct 2005, 12:26 a.m.,in response to message #42 by James M. Prange (Michigan) Quote: By the way, I strongly suspect that what Palmer had in mind was a proposed additional rule, suggested by the famous astronomer John Herschel, that years divisible by 4000 not be leap years. The current Gregorian calendar is slow by 25.92 seconds/year (much better than the 11 1/2 minutes of the Julian calendar!); the Y4K proposal makes it slow by 4.32 seconds/year. However, that means that there will be a Y20K problem. Note too that the Eastern Orthodox church in 1923 proposed an alternative rule to correct the leap year problem in the Julian calendar. In their system, century years modulo 900 must have a value of 200 or 600 to be considered a leap year. This first year of divergence is in 2800, where the Gregorian calendar has a leap year but the Orthodox calendar does not until 2900. The Orthodox calendar is slow by 1.91 seconds/year, so their day of reckoning doesn't happen until Y45K. An additional problem is that the end of the current interglacial period (not "the next ice age" since we're in the middle of an ice age now!) is due around Y25K and may cause further perturbations on the Earth's rotation and revolution.

 Re: Watch out for Y2KMessage #79 Posted by Dave Shaffer on 5 Oct 2005, 11:10 a.m.,in response to message #78 by blurdybloop re: "An additional problem is that the end of the current interglacial period (not "the next ice age" since we're in the middle of an ice age now!) is due around Y25K and may cause further perturbations on the Earth's rotation and revolution." As I try to make the difference when I teach Astronomy 101, "rotation" is the turning of the Earth on its axis, whereas "revolution" is the orbital motion of the Earth around the Sun. So, while a new ice age may well affect the rotation rate of the Earth (due to changes in the moment of inertia of an ice-clad Earth) it WILL NOT affect the revolution (i.e. the orbital period). Sorry to be so technical, but when among geeks and nerds, we should make sure we have it right!!

 Re: Watch out for Y2KMessage #80 Posted by blurdybloop on 6 Oct 2005, 12:35 a.m.,in response to message #79 by Dave Shaffer Quote: So, while a new ice age may well affect the rotation rate of the Earth (due to changes in the moment of inertia of an ice-clad Earth) it WILL NOT affect the revolution (i.e. the orbital period). Note that I said "the end of the current interglacial period" and not "the return of the glaciers." The latter is one aspect of the former. Consider the possibility that ice ages and interglacial periods are caused by something that also impacts the revolution of the Earth. That's what I meant when I said "rotation and revolution". Rotation can be affected by the ice, whereas revolution *and* ice could be affected by some common external cause. This is all speculation, of course.

 Re: Watch out for Y2KMessage #81 Posted by James M. Prange (Michigan) on 5 Oct 2005, 10:43 p.m.,in response to message #78 by blurdybloop My impression is that the additional rule was actually adopted by the Greek Orthodox church, and also that for Russia (and I suppose maybe some others), this is the official calendar. I hope that everyone will agree on a uniform civil calendar before the Gregorian and Orthodox calendars get out of synch in 2800. I wouldn't expect lunar calendars for religious and traditional uses to be abandoned though. Regarding ice ages, land in many northern (and southern?) regions is still rebounding from the last big melt-off, so mass is being redistributed closer to Earth's axis. I'd expect this "glacial rebound" to tend to speed up the earth's rotation, opposing tidal braking's slowing of it. Then too, glaciers at all latitudes seem to be shrinking currently, which surely has some effect on the distribution of Earth's mass. What happens if (when?) the ice caps on Greenland and Antarctica melt or slide into the ocean? I suppose for one thing, for most people, whether the vernal equinox falls very near March 21st will be among the least of their problems. Of course the distribution of inland water varies, largely due to human engineering. Ocean and atmospheric currents (and their portion of the angular momentum) vary, and the distribution of mass in the oceans and atmosphere varies (El Nino and so on). I've read that Earth's core rotates at a different rate than its crust, and the "slippage" probably varies, thus changing the distribution of angular momentum. Quite a lot of things affect the distribution of Earth's angular momentum, and the rotation has to change to conserve total angular momentum. Well, of course in the case of tidal braking and the moon moving farther out, it's the angular momentum of the Earth-Moon system that's being conserved. As it seems difficult to predict the exact distribution of angular momentum of, it's also difficult to predict the exact rotation. But all of the above affects Earth's rotation (its day length), not it's revolution (year length). They would be relevant for leap seconds (or occasionally dropping a second) or redefining a second to make 86400 seconds closer to 1 mean solar day. To the extent that the average length of a day varies, the number of such days in a year must vary too. To affect the revolution, we need something outside of the Earth-Moon system, such as perturbations from other planets, or perhaps the solar wind or impact with extra-planetary "dust". My understanding is that it's perturbation from the major planets that causes the precession of Earth's perihelion (no, this isn't the same as the "precession of the equinoxes"). Regards,James

 Re: Watch out for Y2KMessage #82 Posted by blurdybloop on 6 Oct 2005, 12:25 a.m.,in response to message #81 by James M. Prange (Michigan) Quote: To affect the revolution, we need something outside of the Earth-Moon system, such as perturbations from other planets, or perhaps the solar wind or impact with extra-planetary "dust". My understanding is that it's perturbation from the major planets that causes the precession of Earth's perihelion (no, this isn't the same as the "precession of the equinoxes"). Hence my reference to the Earth's revolution; as we are not certain what causes ice ages, we need to consider the possibility that it is due to something external to the Earth-Moon system.

 Re: Watch out for Y2KMessage #83 Posted by R Lion (Spain) on 1 Oct 2005, 2:59 a.m.,in response to message #23 by Palmer O. Hanson, Jr. The 67 program, and the 41 and 42 versions I rewrote, give 366 :-(

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