[LEAPSECS] alternative to smearing

[Preben Nørager]

On Tue Jan 10 08:23:50 EST 2017, Zefram wrote:


"He [Newcomb] envisions negative JDs, and we have no difficulty extending
numbers in that direction as far as we care to go. The JD system thus does
cover all of history."


Let's say Newcomb envisions negative JDs, and astronomy thus uses the JD
system. Astronomy then have two different "eternal" timescales, with two
different starting points for zero: The one is the proleptic gregorian
calendar, represented by ISO 8601, with the starting year zero, and the
other the JD system, with the starting day zero.


I understand the need in astronomy, and computer science, for a continuous
timescale, and I understand that continuous days, and fractions of days, is
better suited that need, than continuous
years:months:days:hours:minutes:seconds. But I don't understand how
astronomy can cope with two different starting points for zero. The
beginning of time must be a beginning in time, and I don't see how
astronomy can have a day zero, that is different from the year zero. The
zero point in time must somehow be the same for both the daily, and the
annual timescale.


The way I see the JD system being used in astronomy, it is as the
fundamental timescale. The number of JD is related to the days in either
the julian or the gregorian calendar, but the proleptic gregorian calendar,
with year zero, is not really being used. I don't know if that is because
Christmas day (December 24/25), and other important days, are not the same
JD in the julian, and the proleptic gregorian calendar, but either way, the
zero point in time must be the same for both the daily, and the annual
continuous timescale.


I propose to reform the JD system with a new system of proleptic gregorian
days GD. The proleptic gregorian calendar, with year zero, shall be the
fundamental timescale, and in that calendar each year has either 365 or 366
days, in accordance with the gregorian leap year rules. Year 0 is a leap
year.


The new system of GD shall like JD count the days from noon to noon. But
the zero day shall not be JD:0. The zero day of GD shall be the day from
-0001-12-31T12:00 to 0000-01-01T12:00. That day is JD:17210159, so my
reform will be the removal of 17210158 days from JD, to create GD.


With the new timescale I propose, negative years and negative days will
always be the same, and that I think is important. The days from midnight
to midnight, in the proleptic gregorian calendar, will of course always be
positive, from 1 to 365/66, but in negative years all GD will also be
negative.


"Time is a continually flowing quantity" (Newcomb, Compendium, 1906, p.
123).


-Preben


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