Actually posted in comp.os.vms:
>Newsgroups: vmsnet.misc
>From: nick@nick01.demon.co.uk (Nick de Smith)
>Subject: Re: Date Time SPR
>References: <CotxGB.J85@umassd.edu>
>Organization: his office
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In article <CotxGB.J85@umassd.edu> hshubs@cis.umassd.edu writes:
> I'm looking for the infamous Date/Time SPR response in which a DECcie
> told a customer, in excruciating detail, why 2000 is a leap year. Would
> someone please repost it?
I'm reposting this as its been a while since it was seen...
The author of this was "Stanley Rabinowitz", famous in the DEC world
as the author of the SMG$ library, the WHAT utility and many other parts of VMS
.
The copyright of this is therefore probably his, but he has now left DEC.
This copy was sent to me when I worked for DEC in France in 1983, so its only
"second hand" - i.e. it came to me direct from STAR::
Enjoy...
Nick nick@nick01.demon.co.uk
?|?|?|?|? cut here ?|?|?|?|?|??|
Posted-date: 14-OCT-1983 @ 03:08:00
Subject: My SPR answer (for your review)
SPR NUMBER: 11-60903
ANSWER CATEGORY: UE
MAINTENANCE HOURS: 1
DUPLICATE PROBLEM: N
DUPLICATE SPR NUMBER(S):
OPERATING SYSTEM: VAX/VMS
O.S. VERSION: V3.2
PRODUCT: VAX/VMS
PRODUCT VERSION: V3.2
COMPONENT: Run-Time Library
SUB-COMPONENT: LIB$ routines
DATE ANSWERED: 13-Oct-1983
MAINTAINER: Stanley Rabinowitz
ATTACHMENT: N
PUBLICATION INSTRUCTIONS: N
SPR PROBLEM ABSTRACT: User claims year 2000 should not be a leap year.
TITLE: -
PUBLICATIONS: -
ADDITIONAL O.S. VERSIONS:
ADDITIONAL PRODUCT VERSIONS:
COMPONENT SEQUENCE NUMBER:
SUPERSEDES:
TYPE OF ARTICLE:
ANSWER CATEGORIES
CG=1=CORRECTION GIVEN RS=5=RESTRICTION SG=9=SUGGESTION
FN=2=FIXED IN NEXT RELEASE CS=6=CUSTOMER SUPPORTED IQ=10=INQUIRY
DE=3=DOCUMENTATION ERROR NR=7=NON-REPRODUCIBLE HW=11=HARDWARE
UE=4=USER ERROR II=8=INSUFFICIENT INFORMATION
TYPE OF ARTICLE
F=OPTIONAL FEATURE PATCH N=NOTE
M=MANDATORY PATCH R=RESTRICTION
FOR MAINTENANCE USE
D I G I T A L
SPR ANSWER FORM
SPR NO. 11-60903
SYSTEM VERSION PRODUCT VERSION COMPONENT
SOFTWARE: VAX/VMS V3.2 VAX/VMS V3.2 Run-Time Library
PROBLEM:
The LIB$DAY Run-Time Library service "incorrectly" assumes the year 2000 is a
leap year.
RESPONSE:
Thank you for your forward-looking SPR.
Various system services, such as SYS$ASCTIM assume that the year 2000 will be a
leap year. Although one can never be sure of what will happen at some future
time, there is strong historical precedent for presuming that the present
Gregorian calendar will still be in affect by the year 2000. Since we also hope
that VMS will still be around by then, we have chosen to adhere to these
precedents.
The purpose of a calendar is to reckon time in advance, to show how many days
have to elapse until a certain event takes place in the future, such as the
harvest or the release of VMS V6. The earliest calendars, naturally, were crude
and tended to be based upon the seasons or the lunar cycle.
The calendar of the Assyrians, for example, was based upon the phases of the
moon. They knew that a lunation (the time from one full moon to the next) was 2
9
1/2 days long, so their lunar year had a duration of 354 days. This fell short
of the solar year by about 11 days. The exact time for the solar year is
approximately 365 days, 5 hours, 48 minutes, and 46 seconds. After 3 years,
such a lunar calendar would be off by a whole month, so the Assyrians added an
extra month from time to time to keep their calendar in synchronization with th
e
seasons.
The best approximation that was possible in antiquity was a 19-year period, wit
h
7 of these 19 years having 13 months (leap months). This scheme was adopted as
the basis for the religious calendar used by the Jews. The Arabs also used this
calendar until Mohammed forbade shifting from 12 months to 13 months.
When Rome emerged as a world power, the difficulties of making a calendar were
well known, but the Romans complicated their lives because of their superstitio
n
that even numbers were unlucky. Hence their months were 29 or 31 days long, wit
h
the exception of February, which had 28 days. Every second year, the Roman
calendar included an extra month called Mercedonius of 22 or 23 days to keep up
with the solar year.
Even this algorithm was very poor, so that in 45 BC, Caesar, advised by the
astronomer Sosigenes, ordered a sweeping reform. By imperial decree, one year
was made 445 days long to bring the calendar back in step with the seasons. The
new calendar, similar to the one we now use was called the Julian calendar
(named after Julius Caesar). It's months were 30 or 31 days in length and every
fourth year was made a leap year (having 366 days). Caesar also decreed that th
e
year would start with the first of January, not the vernal equinox in late
March.
Caesar's year was 11 1/2 minutes short of the calculations recommended by
Sosigenes and eventually the date of the vernal equinox began to drift. Roger
Bacon became alarmed and sent a note to Pope Clement IV, who apparently was not
impressed. Pope Sixtus IV later became convinced that another reform was needed
and called the German astronomer, Regiomontanus, to Rome to advise him.
Unfortunately, Regiomontanus died of the plague shortly thereafter and the plan
s
died as well.
In 1545, the Council of Trent authorized Pope Gregory XIII to reform the
calendar once more. Most of the mathematical work was done by Father Christophe
r
Clavius, S.J. The immediate correction that was adopted was that Thursday,
October 4, 1582 was to be the last day of the Julian calendar. The next day was
Friday, with the date of October 15. For long range accuracy, a formula
suggested by the Vatican librarian Aloysius Giglio was adopted. It said that
every fourth year is a leap year except for century years that are not divisibl
e
by 400. Thus 1700, 1800 and 1900 would not be leap years, but 2000 would be a
leap year since 2000 is divisible by 400. This rule eliminates 3 leap years
every 4 centuries, making the calendar sufficiently correct for most ordinary
purposes. This calendar is known as the Gregorian calendar and is the one that
we now use today. It is interesting to note that in 1582, all the Protestant
princes ignored the papal decree and so many countries continued to use the
Julian calendar until either 1698 or 1752. In Russia, it needed the revolution
to introduce the Gregorian calendar in 1918.
This explains why VMS chooses to treat the year 2000 as a leap year.
Despite the great accuracy of the Gregorian calendar, it still falls behind ver
y
slightly every few years. If you are very concerned about this problem, we
suggest that you tune in short wave radio station WWV, which broadcasts
official time signals for use in the United States. About once every 3 years,
they declare a leap second at which time you should be careful to adjust your
system clock. If you have trouble picking up their signals, we suggest you
purchase an atomic clock (not manufactured by Digital and not a VAX option at
this time).
END OF SPR RESPONSE
Jesper Nilsson // dat92jni@ludat.lth.se or jesper@df.lth.se