On 2005-08-15 15:04, "Doug McNutt" <[EMAIL PROTECTED]> 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 = JD 2,400,000.5. > 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. :)
