Re: Date and time on Cindu: yearly update

On Mon, May 19, 2008 at 10:28 PM, Michael Poxon <mike@...> wrote:
> Yes, and astronomers still use that time, called strictly GMAT (G.M.
> Astronomical Time), especially in conjunction with the JD (Julian Date)
Gah.  Unfortunately, "Julian Date" is an overloaded term which can
also mean simply the date in the Julian calendar and is also often
used (incorrectly) to mean the day number within the current year.  So
while astronomers distinguish between "Julian Day" (integral value)
and "Julian Date" (value with fraction indicating time of day), I just
lump them both togther as "Julian Day" or, better yet, the unexpanded
acronym "JD", to avoid confusion.  Another possibility I've seen used,
along the GMAT lines, is "Julian Astronomical Day/Date" or "JAD".

> which numbers days sequentially from a zero point in about 4700 BC.
More specifically, JD 0 = noon GMAT January 1st, 4713 BC Julian =
November 24th, -4713 Gregorian.  As I type this it is approximately JD
2,454,605.611.


--
Mark J. Reed <markjreed@...>

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