>NOTE: We are using the astronomer's True Julian Day (eg, May 23, 1968
is
>2,400,000), which should not be confused with the "year-day" (eg, Feb
2
>is year-day 33). The "year-day" is frequently called julian day
>(incorrectly) by oceanographers and meteorologists. Our two-integer
>time word (word1=True Julian Day, word2=milliseconds since midnight of
>the True Julian Day) allows millisecond accuracy for time periods
>extending over centuries.
I agree that using Julian Day, and number of milliseconds since midnight of
the Julian day is a good way to store time data.
However, does it introduce some possible confusion? The following is from
"Numerical Recipes in C", 2nd Ed., p. 12.
"Astronomers number each 24-hour period, starting and ending at noon, with
a unique integer, the Julian Day Number."
That is, Julian Day Number 2440000 starts at 1200 GMT on 23 May 1968, not
at 0000 GMT.
So do you
(a) Assume that the Julian Day number is to be strictly interpreted, and
start the millisecond count at 0 at 1200 GMT on the calendar date (e.g. 23
May 1968) in question,
or
(b) Assume that the calendar date holds precedence, start the millisecond
count at 0 at 0000 GMT on the calendar day in question, and interpret the
Julian Day as starting and ending at the same times as the calendar day.
Just wondering....
Cheers,
Liam.
-- Liam E. Gumley Code 913 (Climate and Radiation Branch) Phone (301) 286-8789 NASA Goddard Space Flight Center Fax (301) 286-1759 Greenbelt MD 20771, USA gumley@climate.gsfc.nasa.gov