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Re: Kodiak Star Launch 80% GO



>> WRONG!!!! -- the day=266 is >>NOT<< the Julian date (JD). The current 
>> Julian
>> Date is 2,452,174 and it represents the elapsed number of days since 
>> ~4713
>> BC (approximately the date that the good Rev. Usher ascribed to the
>> Creation).
>>
>> Because this is an inconveniently large number, the term Modified 
>> Julian
>> Date (MJD) is given by
>> the equation JD-2,400,000.5 making the current MJD be 52175. The 
>> reason for
>> the 0.5 on the end of the constant is that JD is reckoned from Noon 
>> whilst
>> more common usage has the day beginning at midnite UTC (=GMT="z"). When
>> scientists use MJD, it is common to add the fraction of a day to this, 
>> so as
>> I write this message at ~00:40:00 UTC, the MJD is ~52175.03. The 
>> Calendar
>> date corresponding to MJD=0 was in November, 1842.
>>
>> The other continuous date we often see used is the "Excel" date 
>> (which I
>> call XD). Excel uses elapsed days since Jan 0th, 1900 (i.e. 
>> Dec.31,1899),
>> making it now be XD=37157. Obviously, MJD=XD+15018.

Of course, there's also Unix time, which is an unsigned integer count of 
seconds since a certain date in the 1970's which escapes me at the 
moment.  It's a rather large number .. ;-) .. but this is one reason 
*nix systems typically go kerblooey if the clock date is set to 
something before 1970.  It's not a continuous *date*, of course, but 
given the notoriously non-decimal nature of our other time units, it 
does have a certain appeal ..

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