Conference 7.286::digital

    2000 should be a leap year.
    
    I'll try to find a reference, but the rule is something like:
    a "normal" year is a leap year if it's wholly divisible by 4;
    a "century" year is a leap year if it's wholly divisible by 400.

    For example, 1900 was not a leap year (1900/400=4.75), 
    but 2000 is (2000/400=5).

    Every year that is divisible by 4 is a leap year, except if it is
    divisible by 100, except if it is divisible by 400.
    
    1800 no    1900 no    2000 yes    2100 no    2200 no    2300 no    2400 yes
    
    Helmut

    It takes 365.25 days for the earth to rotate around the sun. Every four
    years we add a day to keep the seasons from getting out of balance. It
    has nothing to do with the numeric counting of years. We need one extra
    day every four years.
    
                                  Steve J.

    http://www.sprinc.com/marktime.htm
    
    In October, 1582 Pope Gregory XIII implemented the following changes to
    the old Julian Calendar:
    
    New Year's day changed from March 25 to January 1. 
    
    The calendar advanced by 10 days, making the day after Oct 4, 1582
    into Oct 15, 1582. 
    
         Updated and refined Leap Year rules: 
    
    1.Years evenly divisible by four are to be considered Leap
    Years. 
    
    2.Century years (double 00) must be evenly divisible by 400
    (2000 is a leap year). 
    
    3.The years 4000, 8000, and 12000 are considered to be "common
    years" (not leap years).
    
    4.Century years divisible by 900 will be leap years only if the
    remainder is 200 or 600 (2000 is a leap year).

    
    See 4514.3 for the full story.
    
    JP

    Well, I learned something new. In my lifetime, my rule will work fine.
    I never realized thatwe skipped leap years before.
    
                                Steve J.

    Re .4:
    
    > It takes 365.25 days for the earth to rotate around the sun.
    
    365.2422.
    
    
    				-- edp
    
    
Public key fingerprint:  8e ad 63 61 ba 0c 26 86  32 0a 7d 28 db e7 6f 75
To find PGP, read note 2688.4 in Humane::IBMPC_Shareware.

>         <<< Note 5128.5 by USPS::FPRUSS "Frank Pruss, 202-232-7347" >>>
>
>    4.Century years divisible by 900 will be leap years only if the
>    remainder is 200 or 600 (2000 is a leap year).
    
    If a century year is divisible by 900, doesn't that mean that the
    remainder is always zero?
    
    John

       <<< Note 5128.8 by RUSURE::EDP "Always mount a scratch monkey." >>>

>    Re .4:
>    
>    > It takes 365.25 days for the earth to rotate around the sun.
>    
>    365.2422.
>    
>    
>    				-- edp
 
Since you nitpicked, it should probably be 'revolve', not 'rotate' :-).
   
-Joe

|    http://www.sprinc.com/marktime.htm
|    
|    In October, 1582 Pope Gregory XIII implemented the following changes to
|    the old Julian Calendar:
|    
|    New Year's day changed from March 25 to January 1. 
|    
|    The calendar advanced by 10 days, making the day after Oct 4, 1582
|    into Oct 15, 1582. 
|    
|         Updated and refined Leap Year rules: 
|    
|    1.Years evenly divisible by four are to be considered Leap
|    Years. 
|    
|    2.Century years (double 00) must be evenly divisible by 400
|    (2000 is a leap year). 
|    
|    3.The years 4000, 8000, and 12000 are considered to be "common
|    years" (not leap years).
|    
|    4.Century years divisible by 900 will be leap years only if the
|    remainder is 200 or 600 (2000 is a leap year).

	Don't forget that the new rules did not come into effect
	in 1582. Different countries adopted the Papal decreee at
	different times. Some joined immediately, while others
	waited. The American colonies went with their colonial powers
	which is why George Washington has two birthdays. Russia
	did not adopt until the revolution, which is why their
	"fudge factor" is much greater than those who joined earlier.

	>Per

    The actual length of a year is NOT 365.25 days but slightly less,  365
    days 5 hours 48 minutes and 46 seconds.  If you calculate the error per
    year then it is almost correct with the previously mentioned rules
    (leap year, century rules etc.)  
    
    If the leap year calendar were invented now rather than back in 1582
    then we would probably have created a slightly different solution. 
    Since we all use computers and everyone is more literate we could have
    used the 4year leap year rule but replaced the century rules with
    not having a leap year every 128 years.  The 400 year rule is not
    needed and the error will not accumulate to a full days error for
    approx 30,000 years.  (got all this from my encyclopedia).  I
    personally will not care at that point how we solve the problem...
    
    Also,  don't forget that the year is getting longer at approx 1 second
    per century.
    
    That should be all anybody needs to know - and more than anybody cares
    about...
    
                                                               

>    Also,  don't forget that the year is getting longer at approx 1 second
>    per century.
    
Eh?  I know the Earth's rotation is slowing due to tidal effects, 
and the moon is moving farther from the Earth due to the same, 
but is the same effect occuring for the Earth-Sun interaction?

>    That should be all anybody needs to know - and more than anybody cares
>    about...
    
Sorry.                                                               

Wes

    In 1967, the 13th General Conference on Weights and Measures chose
    to replace time reckoning based on astronomical measurements, since
    planetary rotation may change over time.  The current standard for 
    all time measurement, the second, was redefined from 1/86400 of a "day", 
    to 9,192,631,770 cycles or vibrations within a hyperfine electron level 
    of the cesium atom.  
    
    Every so often, usually around June 30th or December 31st, a "leap
    second" may be added to adjust things, if you really want to nitpik.
    
    P.S. I have not checked the spelling of any of the above.  
    If this failure on my part offends anyone, I am SOOOOOOOO sorry!

    Re .14:
    
    >     Every so often, usually around June 30th or December 31st, a "leap
    > second" may be added to adjust things, if you really want to nitpik.
                     ^^^^^
    
    Or subtracted.  The Earth's rotation isn't just speeding up or slowing
    down -- it varies, and sometimes seconds are skipped instead of added.
    
    
    				-- edp
    
    
Public key fingerprint:  8e ad 63 61 ba 0c 26 86  32 0a 7d 28 db e7 6f 75
To find PGP, read note 2688.4 in Humane::IBMPC_Shareware.

re .5:

>    3.The years 4000, 8000, and 12000 are considered to be "common
>    years" (not leap years).

This is not part of Pope Gregory's change.  It is an idea proposed by some
that would keep the calendar accurate longer.  An even more accurate change
would be to have every 3200 years (not every 4000) be common years.  (3300
years is even better but 3200 would follow the existing pattern) 
    
>    4.Century years divisible by 900 will be leap years only if the
>    remainder is 200 or 600 (2000 is a leap year).

This conflicts directly with Rule 2, which should read:

    2.Century years (double 00) must be evenly divisible by 400 to be a leap
    year, else they are common years.
    (2000 is a leap year, 1900 wasn't). 
    
#4, however, is a rule used by the Russian Orthodox Church, and is more
accurate than the Gregorian Calendar (unless the 3200 year rule is added).  It
will be the same as the Gregorian Calendar until the day after Feb 28, 2800. 

re: .15

There have been no negative leap seconds and it is unlikely that 
there will ever be one.

There aren't many phenomena that cause the Earth's rotation to
speed up or otherwise jump ahead of UTC.  A collision with a
comet or asteroid might do it. 

AltaVista search on "leap second" gives lots of info.

Wes

Here is info on the dates on which various places adopted the Gregorian
calendar:

Prior to 1923, the Julian calendar was still in use in some countries.
The date above is according to the Gregorian calendar, which was first
adopted by Spain and her colonies (including Florida) the day following
Oct 4th, 1582, which was reckoned as Oct 15th.  Gradually, other nations
adopted the Gregorian calendar: the Catholic German states in 1583; the
Protestant German states in 1699; England and her colonies in September
1752; Sweden in 1753; Alaska upon purchase in 1867; Japan in 1873; China
in 1912; the Soviet Union in 1918; and Greece in 1923.  In Switzerland,
both calendars were in use from 1583 until the country was fully converted
in 1812.

|    The 400 year rule is not
|    needed and the error will not accumulate to a full days error for
|    approx 30,000 years.  (got all this from my encyclopedia).  I
|    personally will not care at that point how we solve the problem...
 
    Actually, along about the year 2525, we got tired of calendars
    altogether and since then every day is Saturday, August 3, and we
    don't bother with years at all.
    
    Computers do all the work now.
    
    	/Time Traveller   

The adoption of the Gregorian Calendar by the Soviet Union in 1918 is why
their October Revolution anniversary was celebrated in November.

Note that Russia and Greece are primarily Orthodox Christian counties, 
which did not recognise the supremacy of the Pope.  This would explain 
their delay in adopting Pope Gregory's calendar.

I believe there is a famous story where Napolean agreed to meet the 
Russsian forces at a certain date, but the Russian were 10 days date due to 
the different calendar.  Opps!


							-Paul

| I believe there is a famous story where Napolean agreed to meet the 
| Russsian forces at a certain date, but the Russian were 10 days date
| due to the different calendar.  Opps!

Napoleon also had his own calendar for a while, different from the pre
and post gregorian calendar. Only lasted for a few years, though. Perhaps
that contributed to the conversion problems :^)

>Per

>> It takes 365.25 days for the earth to rotate around the sun.
>   
> 365.2422.

	I thought it was 365.24219, at least for a Tropical year
	(equinox to equinox).

	There are also Siderial, Anomalistic, Eclipse and Gaussian
	years,the shortest being the Eclipse year (Moon's node to 
	Moon's node) at 346.62003 and the longest being the Anomalistic 
	year (apse to apse) at 365.25964.

>	Moon's node) at 346.62003 and the longest being the Anomalistic 
>	year (apse to apse) at 365.25964.

Perhaps it wouldn't be so long if the astronomers would get off their apse.

    What a wealth of information notes is, thanks for the explanation, now
    I can straighten out the non-believers..
    
    	Regards,
    	Steve.

So -- is 2000 a leap year?   :-)

    >>> So -- is 2000 a leap year?   :-)
    
    Yes

    according to what used to be the National Bureau of Standards (the
    organization that runs the time radio stations WWV and WWVH and keeps
    the national atomic clock ... and these people ought to know!) the year
    2000 is absolutely a leap year.
    
    

> the year 2000 is absolutely a leap year.

Jump for joy; I'd hate to go 8 years between February 29ths. 

dxcalendar (DECwindows calendar) concurs. 

dtcm (cde calendar) agrees. dxcalendar says 2100 is not a leap year. 
dtcm says it only goes to 2038. 

>dtcm says it only goes to 2038. 

Shoot, I can't put my 83rd birthday party on the calendar.

Wes

    I believe 2038 is when unix expires. The standard date keeping in unix
    will run out of 32 bits then.

    > I believe 2038 is when unix expires. The standard date keeping in unix
    > will run out of 32 bits then.
    
    That's when it runs out of 31 bits and time turns negative.
    
    If you fix code to use unsigned then you get another 68 years.
    
    60*60*24*365*68 is 2144448000.  Unix epoch is Jan 1 1970 GMT and time
    is in seconds.
    
    Steveg

Microsoft Windows 95 and MS Project both agree 2000 is a leap year.

So it MUST be true.

Brian.

re: .32

>    > I believe 2038 is when unix expires. The standard date keeping in unix
>    > will run out of 32 bits then.
>    
>    That's when it runs out of 31 bits and time turns negative.
    
Ah, then we all start getting younger -- I like it!!!

Wes

>Microsoft Windows 95 and MS Project both agree 2000 is a leap year.
>
>So it MUST be true.
>
>Brian.

Well, thats the definitive answer of course.  We should have looked there
first.  What were we thinking.

    
U.S. Naval Observatory
USNO Press Release                              February 11, 1997
Dr. Dennis McCarthy, 202-762-1837

U.S. Naval Observatory to Add Leap Second to Clocks

On June 30, 1997 a leap second will be added to the world's clocks at
23 hours, 59 minutes and 59 seconds Coordinated Universal Time (UTC).
This corresponds to 7:59:59 pm Eastern Daylight Time, when the extra
second will be inserted at the U.S. Naval Observatory. This marks the
21st leap second to be added to UTC, a uniform time kept by atomic
clocks (although you normally don't think about it, for most
conventional uses the time you use is UTC). At the U.S. Naval
Observatory time is determined by averaging the time signals from
cesium beam and hydrogen maser atomic clocks.

Man's oldest clock has been the Earth. We know it's morning when the
Sun rises, noon when the Sun is overhead, and evening when the Sun
sets. The Earth's accuracy as a clock is good to about one thousandth
of a second per day -- more than enough accuracy for most people.
However, the invention of "atomic" clocks, which operate by measuring
the resonant frequency of a given atom -- currently Cesium, Hydrogen or
Mercury -- greatly increased that accuracy, and has now led to the
capability at the U. S. Naval Observatory of measuring time to
accuracies exceeding a billionth of a second per day.

Time measured by the rotation of the Earth is not uniform when compared
to the time kept by atomic clocks. In fact, radio telescopes now
observe the most distant objects in the universe, known as quasars, to
determine the irregularities in the Earth's rotation. As a result of
such irregularities, the atomic clocks get out of sync with the Earth.

In 1972, by international agreement, it was decided to let atomic
clocks run independently of the Earth, keep two separate times, and
coordinate the two. In order to keep the difference between Earth time
and atomic time within nine tenths of a second as the two times get out
of sync, leap seconds are added to the atomic time scale. The
International Earth Rotation Service (for which the U. S. Naval
Observatory provides the rapid service) is the organization which
monitors the difference between the two time scales and calls for leap
seconds to be inserted when necessary. Since 1972, leap seconds have
been added at intervals varying from six months to two-and-one-half
years -- this leap second is eighteen months since the last one. Leap
seconds are added because the Earth's rotation tends to slow down. If
the Earth were to speed up, a leap second would be removed.

The U. S. Naval Observatory is charged with the responsibility for
precise determination and management of time dissemination, and as such
provides the Master Clock for the Department of Defense and the entire
nation. Modern electronic systems, such as electronic navigation or
communication systems, depend increasingly on precise time and time
interval (PTTI). Examples are the ground-based LORAN-C navigation
system and the satellite based Global Positioning System (GPS).

These systems are all based on the travel time of the electromagnetic
signals: an accuracy of 10 nanoseconds (ten one-billionths of a second)
corresponds to a positional accuracy of about 10 feet. In fast
communications, time synchronization is equally important. All of these
systems are referenced to the U. S. Naval Observatory Master Clock.

The present Master Clock, accurate to better than a billionth of a
second per day, is based on a system of over 50 independently operating
cesium atomic clocks and 10 hydrogen maser atomic clocks. These clocks
are distributed over 12 environmentally controlled clock vaults, to
insure their stability. By automatic hourly intercomparison of all
clocks, a time scale can be computed which is not only reliable but
also extremely stable. On the basis of this computed time scale, a
clock reference system is steered to produce clock signals which serve
as the U. S. Naval Observatory Master Clock.

The U. S. Naval Observatory's success in its time standard function is
evident in the fact that it is the largest single contributor to the
international time scale (UTC), which is computed in Paris, France, at
the International Bureau of Weights and Measures. Moreover, its
principal role in keeping track of the change in the "Earth clock"
(i.e., Earth rotation) and its dissemination of this information as the
Rapid Service Sub-bureau for the International Earth Rotation Service
attests to the fact that globally, as well as nationally, the U. S.
Naval Observatory remains the leader in precise time.

A press kit, including illustrations of the Master Clock and a VLBI
antenna, are available upon request from the Public Affairs Office at
202-762-1438.


---
Andrew Yee
ayee@nova.astro.utoronto.ca

sheesh...
I only wanted to know if it was time for a geedunk

    re: .36
    

    Why couldn't they simply synchronize it with the switch to Daylight
    Savings Time so we only have to change our clocks once?

    
    	What a bunch of comedians.
    
    	8^)
    

CAn those guys set my VCR timer?

gc

    Those guys have too much time on their hands!
    
    

Re .39: whose daylight savings time are you referring to?

PJDM

    re .43
    
    It had better not be Arizona's.