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Postings from August 2005
From: Mark Reed
August 15, 2005 13:08
Message ID: BF266E79.B3EAfirstname.lastname@example.org
On 2005-08-15 15:04, "Doug McNutt" <email@example.com> wrote:
> At 13:31 -0400 8/15/05, Mark Reed wrote:
> If anyone gets serious about Julian dates there is also the Modified Julian
> Date, MJD, used by the US military and others. It differs from the JAD above
> by a large well-defined integer plus 1/2.
The (then) most recent even multiple of 100,000 was chosen for it: MJD 0 =
> The result is a day that begins at
> midnight and starts at a more recent date that I don't remember. It's not Jan
> 0, 1970 though.
November 17, 1858. Which, while not Jan 1, 1970, is still time zero for
another operating system some of you may have heard of: VMS.
There's also something called the Truncated Julian Day/Date, or TJD, which
NASA used to use: it was essentially the last four digits of the MJD, so
that TJD 0 was MJD 40000, aka May 24, 1968. But once MJD 50000 rolled
around (on Oct 10, 1995), the TJD became ambiguous. Besides, while saving a
decimal digit of storage per log entry was significant when NASA was trying
to get computers light enough to launch in the 1960s, it's not exactly an
earth-shattering storage win today. So the TJD is best avoided. In fact,
forget I mentioned it. :)