Re: OT: Celestial maps

On Jan 12, 2008 3:10 PM, Lars Finsen <lars.finsen@...> wrote:
> Den 12. jan. 2008 kl. 20.23 skreiv Mark J. Reed:
>
> > Exactly when that year was depends on what you're talking about.  We
> > currently use the Gregorian calendar, and sometimes astronomers extend
> > it backwards well before its inception in 1582 to refer to past dates.
> >  But usually dates before then are given in the Julian calendar,
>
> Astronomers used to reckon time in Julian days, before and after
> 1582. Has that changed in later years?
Astronomers still use Julian days, but mostly for calculations.
Descriptions like "the total solar eclipse of JD 2,454,680" are not
very meaningful, even to astronomers, without a conversion to a more
conventional calendar system.

For the year 0 CE = 1 BCE = AUC 753, the Julian Day that begins at
noon UTC on each January 1st is as follows:

January 1, proleptic Julian calendar          = JD 1,721,058
January 1, contemporary Julian calendar = JD 1,721,059
January 1, proleptic Gregorian  calendar  = JD 1,721,060

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

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