Is year 2000 a leap year??
Author Message
Is year 2000 a leap year??

: I've read/seen somewhere that the year 2000 is not a leap year.  Has anybody
: else seen this?  Is this a true statement??  The code I've seen so
: far doesn't take this into consideration.

Years divisible by 4 are leap years.  The first exception to this is that
years divisible by 100 are NOT leap years (1800, 1900, etc).  Fortunately
for all of that code, the next exception is that years divisible by 400
ARE leap years (overriding the first exception) (1600, 2000, 2400, etc).
There are other exceptions that occur even more infrequently.  Assuming
that your code can handle the turn of the century correctly, you won't
have a leap year problem until the year 2100 (which is about the same time
that all the bugs will be fixed in Windows 95).

Sat, 10 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

Quote:

> : I've read/seen somewhere that the year 2000 is not a leap year.  Has anybody
> : else seen this?  Is this a true statement??  The code I've seen so
> : far doesn't take this into consideration.
> Years divisible by 4 are leap years.  The first exception to this is that
> years divisible by 100 are NOT leap years (1800, 1900, etc).  Fortunately
> for all of that code, the next exception is that years divisible by 400
> ARE leap years (overriding the first exception) (1600, 2000, 2400, etc).
> There are other exceptions that occur even more infrequently.  Assuming
> that your code can handle the turn of the century correctly, you won't
> have a leap year problem until the year 2100 (which is about the same time
> that all the bugs will be fixed in Windows 95).

According to my Webster's dictionary, a leap year is any year that is
evenly divisible by 4, or, in the case of century years, by 400.  This
is the algorithm I've been using.  If there are any other exceptions,
or a more precise definition of leap year, I'd be interested in
learning it.
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Sat, 10 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

(Steven Gross) says:

(after correctly describing the leap year rules)

Quote:
>There are other exceptions that occur even more infrequently.

I don't think so.  These days, they are putting in (or taking out,
but usually putting in) leap seconds as required.  Hence any
drift in clocks over longer periods than 400 years should be
routinely prevented from here on out.

However, that raises the interesting question:  does *anybody's*
timer routine handle leap seconds properly?  It would be difficult.
Leap seconds are only announced a few weeks (or maybe a month or

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Sat, 10 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

Quote:
>I've read/seen somewhere that the year 2000 is not a leap year.

Is this a true statement??

False.  Part of the Gregorian adjustment is that a year divisible by 100 is
not a leap year, except when it is also divisible by 400, in which case it is.

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Sat, 10 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

Quote:

> I've read/seen somewhere that the year 2000 is not a leap year.  Has anybody
> else seen this?

Many people have heard this somewhere or other.  It comes up here all the time.

Quote:
> Is this a true statement??

No, it is not a true statement.  See eg 4 Encyclopaedia Brittanica 569 (1962):

Quote:

> [T]he rule of intercalation is as follows:--
> Every year the number of which is divisible by 4 is a leap year, excepting the
> last year of each century, which is a leap year only when the number of the
> century is divisible by 4; but 4,000, and its multiples, 8,000, 12,000,
> 16,000, etc. are common years.

The year 2000 is the last year of the 20th century.  It will be a leap year
because 20 is divisible by 4.  [Clip 'n' save!]

Quote:
> The code I've seen so far doesn't take this into consideration.

You're lucky.  I've seen a lot of code that thinks the year 2000 is not a leap
year.

--
Christopher Westbury, Midtown Associates, 15 Fallon Place, Cambridge, MA 02138

Sat, 10 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??
I've read/seen somewhere that the year 2000 is not a leap year.  Has anybody
else seen this?  Is this a true statement??  The code I've seen so
far doesn't take this into consideration.

Sat, 10 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

writes:
Quote:
> I've read/seen somewhere that the year 2000 is not a leap year.  Has anybody
> else seen this?  Is this a true statement??  The code I've seen so
> far doesn't take this into consideration.

This has been a rather long-running thread on alt.folklore.computers and
the generally agreed outcome is that under Gregorian calendar rules, every
century year is not a leap year unless the leading two number are divisible
by four.

e.g.  1900 was not a leap year, 2000 will be and 2100 won't be.

The discussion there became rather esoteric and has passed onto leap-seconds
by now.

Charles

Sun, 11 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

JB>      (after correctly describing the leap year rules)

>> There are other exceptions that occur even more infrequently.

JB>    I don't think so.  These days, they are putting in (or
JB> taking out, but usually putting in) leap seconds as required.
JB> Hence any drift in clocks over longer periods than 400 years
JB> should be routinely prevented from here on out.

Leap _seconds_ are needed to stop midnight drifting, because the
length of a day is not constant.

Leap _days_ are needed to stop the Winter Solstice drifting, because the
length of a year in days is not an integer.

The leap day pattern is complex, because the length of a year in days
is not a simple fraction (and not constant).

--
Dave Sparks

Sun, 11 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??
: The discussion there became rather esoteric and has passed onto leap-seconds
: by now.

Charles, you are right...
and I find it very interesting  :-)

IF ((Year MOD 4 = 0) AND (Year MOD 100 /= 0)) OR
(Year MOD 400 = 0) THEN Leap_Year !

;-)

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Team Ada: "C'mon people let the world begin" (Paul McCartney)

Sun, 11 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

Quote:
> Leap _seconds_ are needed to stop midnight drifting,
> because the length of a day is not constant.
> Leap _days_ are needed to stop the Winter Solstice drifting,
> because the length of a year in days is not an integer.
> The leap day pattern is complex, because the length of a year
> in days is not a simple fraction (and not constant).

The relationship between days and years is arbitrary and indirect.
As the Earth's spin slows down then, although one year occupies
the same time period, the number of days reduces dramatically.

There's an Object lesson in there somewhere :-)

--

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=== Independent Computer Consultancy * Established in 1977 ===

Sun, 11 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

Quote:

> (Steven Gross) says:

>   (after correctly describing the leap year rules)

> >There are other exceptions that occur even more infrequently.

> I don't think so.  These days, they are putting in (or taking out,
> but usually putting in) leap seconds as required.  Hence any
> drift in clocks over longer periods than 400 years should be
> routinely prevented from here on out.

The Gregorian calendar as described has a cumulative error of only
a few hours over it's 400 year cycle. I don't know of any other rules.
A candidate rule would be "but not a leap year if it divides by 3200".
There are plenty of special cases for historical dates though.

Quote:
> However, that raises the interesting question:  does *anybody's*
> timer routine handle leap seconds properly?  It would be difficult.
> Leap seconds are only announced a few weeks (or maybe a month or
> two) in advance.

Computers used for astronomical dynamics calculations use an
alternative Ephemeris Time standard (no leap seconds at all).
Comparison of their predictions with astronomical observations
determines when to apply the empirical leap second corrections.

Regards,
--

Scientific Software Consultancy             /^,,)__/

Sun, 11 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

Quote:

> > I've read/seen somewhere that the year 2000 is not a leap year.  Has anybody
> > else seen this?  Is this a true statement??  The code I've seen so far
> > doesn't take this into consideration.

> Yes, you are right. If the year can divide by 400, then it is NOT a leap year.

Well, everyone in comp.lang.cobol may not yet know everything there is to know
about CoBOL, but it's heartening to see that at least we all know our leap
years.

--
Christopher Westbury, Midtown Associates, 15 Fallon Place, Cambridge, MA 02138

Sun, 11 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??
Quote:

. . . . . . . . .
>: I wonder who tried to fool you?    Sure, 2000 is a leap year.
. . . . . . . .
>Sorry, Sven, but it is *not* a leap year if it is divisible by 400.  1600,
>2000, 1400, etc. are *not* leap years.  1900, 1800, 1700, 2100, 2200, 2300,

. . . . . .

Hey, are you trying to fool me?????

Mon, 12 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??
On 25 Jul 1995 00:28:19 GMT,

Quote:
>I've read/seen somewhere that the year 2000 is not a leap year.  Has anybody
>else seen this?  Is this a true statement??  The code I've seen so
>far doesn't take this into consideration.

2000 _IS_ a leap year, because it is divisible by 400.  1900 and 2100 are
not leap years because they are not divisible by 400.  Don't let anyone
tell you differently.

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Mon, 12 Jan 1998 03:00:00 GMT
Is year 2000 a leap year??

: >I've read/seen somewhere that the year 2000 is not a leap year.  Has anybody
: >else seen this?  Is this a true statement??  The code I've seen so
: >far doesn't take this into consideration.
: >
: >
: I wonder who tried to fool you?    Sure, 2000 is a leap year.

: The rule is:
:    any year divisible by 4, excpet centuries which must divide evenly into 400

: (so 1900 was NOT a leap year, you didn't mix up with that one did you?)

: regards Sven

Sorry, Sven, but it is *not* a leap year if it is divisible by 400.  1600,
2000, 1400, etc. are *not* leap years.  1900, 1800, 1700, 2100, 2200, 2300,
2500, etc. *are* leap years.  The 400 year rule corrects 216 seconds/year,
which gives an overall yearly correction of roughly 5 hours, 49 minutes,
12 seconds.  I think the real error is 5:49:11.something, but a one
second per year difference would take 86,400 years to add up to a one day
correction, so we don't have to worry too much about it.  It will probably
change by then, anyway.

Mon, 12 Jan 1998 03:00:00 GMT

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