# RE: Kodiak Star Launch 80% GO

```Duh.... thanks
:-)
Bob

On Sat, 22 Sep 2001, Tom Clark wrote:

> Bob, I hate to bring up topics like this but I feel I must. Your posting a
> few hours ago said:
>
> > [snip] The updated ones will show a julian date of 266.
>
> 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.
>
> The "266" that you incorrectly called the "Julian Date" is properly named
> "Day-of-the-year" which many of us abbreviate DOY. Any attempt to call this
> JD 266 immediately puts you 6700 years behind time!
>
> Anyway -- good luck on the launch a few minutes from now.
>
> 73 de Tom, W3IWI
>

de WB4APR@amsat.org, Bob

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