lmc@denelcor.UUCP (02/23/84)
I have often wondered about the choice of January 1st, 4713 BC as the root of the Julian day numbering system. I have finally found an explanation (in "Counting the Eons", by Isaac Asimov (who else?)), and I thought the net might like to know. Briefly (I hope), the Julian day numbering system as invented by Joseph Justus Scalinger, in 1583. (Julius, by the way, was his slave-driving father, Julius Caesar Scalinger). Essentially, he selected a day from which to count all following days, according to the following requirements: 1. It had to be a January 1st. 2. It had to be a day of a new moon, so that the lunar calendar would be in sync (happens once every 19 years). 3. It had to be a Sunday, in a year with a leap day in it (once in every 28 years). This is known as the solar cycle. 4. It had to be an indiction year (one in which the Romans took their census, set by Diocletian to be every 15 years). This combined solar-lunar-indiction cycle is 7980 years long. Scalinger added one final consideration: 3. It had to occur before ~3500 BC, so that all numbers would be strictly positive (Ussher's estimate of creation at 4004BC was still 40 years in the future; common knowledge at that time said nothing of any events before 3500BC.) And that determined the root of the Julian day counting system. PS: I am interested in various calendar computation routines for computer use. I have a number of them, and I'll soon be sending them out over net.sources. Does anyone out there have access to copies of CACM from the sixties? There are calendar routines in the following references from CACM: Issue 5/62, Issue 7/64, Issue 10/68 If someone could send them along, I'll add them to the collection. -- Lyle McElhaney (hao,brl-bmd,nbires,csu-cs,scgvaxd)!denelcor!lmc