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Archiver > TMG > 2001-09 > 0999365505


From: Richard Brogger <>
Subject: Re: [TMG] Julian days
Date: Sat, 01 Sep 2001 12:31:45 -0500
References: <F1159Lb7FqGNVW2Uiyc000018d6@hotmail.com>


Hi Thomas,

I believe you have totally missed the point but from your message I
can not figure out what you think using Julian days would do. Are
you confusing Julian days with the Julian calendar?

"The Julian period was devised in 1582 by the French classical
scholar Joseph Scaliger (1540-1609) and named after his father
Julius Caesar Scaliger (1484-1558), not after the Julian calendar.
Joseph Scaliger began Julian Day (JD) #1 at noon, Jan. 1, 4713 B.C.,
the most recent time that 3 major chronological cycles began on the
same day-(1) the 28-year solar cycle, after which dates in the
Julian calendar (e.g., Feb. 11) return to the same days of the week
(e.g., Monday); (2) the 19-year lunar cycle, after which the phases
of the moon return to the same dates of the year; and (3) the
15-year indiction cycle, used in ancient Rome to regulate taxes. It
will take 7,980 years to complete the period, the product of 28, 19,
and 15."
The World Almanac® and Book of Facts

A computer works with binary numbers. It knows nothing about 17 Feb
1742. What we enter is not what the computer uses and whether you
call it fixing or translating or whatever, dates get converted. If
all genealogy programs used a standard for dates, all programs would
have the same date range capability. Since they do not have the same
range, I assume they use an arbitrary starting point and the number
of days from that point. How many bits were used to store the
number that represents a date was important because space was
limited. The limit no longer applies but we are stuck with a
limited date range because of it.

As you can see, Jan. 1, 4713 B.C. is not an arbitrary date. It is a
fixed point in time when three cycles began on the same day. With
current computers, storing a 32-bit integer is not a problem. Eric
stated, "If stored in a 32-bit integer, you can keep counting the
days until shortly before the year 6,000,000 AD".

If TMG updates the number, used to store a date, to a 32-bit
integer, that opens a huge window in which to select a starting
point. Any arbitrary date could be used but it would have no
meaning. Why not use an established starting point, Jan. 1, 4713 BC,
that is a world wide standard? If TMG does so, it will be a feature
no other software has. If TMG leads the way, maybe other companies
will follow and 2,450,084 would represent noon of 31 Dec 1995 in all
genealogy programs.

"How many days have you lived? To determine this, multiply your age
by 365, add the number of days since your last birthday until today,
and account for all leap years. Chances are your answer would be
wrong. Astronomers, however, find it convenient to express dates and
time intervals in days rather than in years, months, and days. This
is done by placing events within the Julian period."
The World Almanac® and Book of Facts

To determine a time period (age) in TMG or in Julian days, one
integer is subtracted from another. Before TMG can subtract, it must
convert the dates to an integer. As TMG is now, that integer is
arbitrary and too small to allow a range of dates extending back to
Christ, much less to dates before Christ.

If TMG uses a larger integer, if that integer is based on a
standard, it will not change how you enter dates. Just as one user
might enter 31 Dec 1995, another Dec. 31, 1995 and yet another
31.12.1995 those are all the same dates. TMG converts them to the
same integer. All I am asking is that the integer used for 31 Dec
1995 be the Julian day 2450084. It does not change anything for the
user that entered 31 Dec 1995, that user will still see 31 Dec 1995,
the others will see what they entered, just as they do now.

Richard Brogger

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