Hi John, The difference is there is no difference.
January 1st -4712 is the same as January 1st 4713 BC ( I think the 4173 in your message is a typo error) Atronomers count including the year 0 so the year before 1 is 0 and the year before that is -1. Historians count without the year 0 so the year before 1 is 1 BC and the year before that is -2 BC. Therefore we get two starting points for the Julian day: -4712 4713 BC Jean Meeus uses the astronomical way because it's easier to calculate the JD for the Julian calendar. Best wishes, Fer. Fer J. de Vries De Zonnewijzerkring mailto:[EMAIL PROTECTED] http://www.de-zonnewijzerkring.nl Home mailto:[EMAIL PROTECTED] http://www.iae.nl/users/ferdv/index-fer.htm Eindhoven, Netherlands lat. 51:30 N long. 5:30 E ----- Original Message ----- From: "John Hall" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Saturday, April 26, 2003 9:39 AM Subject: Julian Date and UbiSol > Anselmo I have a couple of questions about your UbiSol Julian Date > (Julian Day). The result for 2003/04/26 seems to be at odds with other > calculators. > > UbiSol = JD 21478.5 > Meeus and others = JD 2452755.5 > > You and other respected references state this date is calculated from > January the 1st 4173 BC. Meeus in his first edition of Astronomical > Algorithms on page 59 states this is calculated from '....... the > beginning of the year -4712' > > Can somebody please help me with an explanation ? > > Confused of Tasmania > 41.5 South 147.1 East > > - > -
