Bible Time

Day Numbers

After the invention of the computer it became important to number days by individual numbers. Astronomers use Julian Day Numbers. This website uses AA Numbers. Both show up in all date reports. What are they, how do they count?

There are many places where days are best known by a simple counting number. This is awkward for people since running math on very large numbers is not particularly easy, but since the invention of the computer this is not a problem.

Julian Day Numbers

These numbers assign day numbers to individual days. For example, consider the following date report for today.

Today
Day	Bible Date	Modern Date	Roman Date	Number
Sun	12999/5/15 AA	11 May 2008 NS	28 Apr 2761 AUC	AA:4741755
	3499/5/15 FE	28 Apr 2008 OS	28 Apr 2008 AD	JD:2454598

The field labeled JD: is the Julian Day number for today.

This day is defined as start at Noon, GMT and running through Noon the next day. This day definition is is NOT considered in the various reports because the current hour is not considered in the computations. If it was it would only confuse the charts since it would not reliably correlate with the other fields.

These numbers have an epoch at JD number 1. The following is the report:

Julian Day number 0, the Julian Epoch
Day	Bible Date	Modern Date	Roman Date	Number
Mon	6270/9/17 AA	24 Nov -4713 NS	19 Sep 4789 BAUC	AA:2287157
	-3230/9/17 FE	1 Jan -4713 OS	19 Sep 5542 BC	JD:0

This epoch is seen best on the OS calendar in the chart above.

AA Numbers

The Julian epoch is not old enough for the purposes of computing Biblical dates while keeping the Julian day number positive.

To provide a similar day counting system this website uses "AA Numbers." This stands for "After Adam Numbers" which start with day number 1 assigned to 1/1/1 AA. The following report shows the AA Number epoch:

AA Number Epoch
Day	Bible Date	Modern Date	Roman Date	Number
Thu	1/1/1 AA	17 Nov -10975 NS	7 Apr 12312 BAUC	AA:1
	-9499/1/1 FE	9 Feb -10975 OS	7 Apr 13065 BC	JD:-2287156

Technically speaking these AANumber days align with the Bible Calendar days. By assigning an Epoch here, all days since the first day of the first year of Adam are numbered with a positive number. This is handy for human calculations and audit purposes across the timeline and throughout the charts.

Zero

Of course both day number counting systems have a day zero allowing days to be counted back past the epoch. The negative Julian Day number for the AA Number epoch can be seen in the previous report.

Dynamic Range

Day numbers on this system are allowed in the range -50,000,000 <= DayNumber <= 50,000,000. This is sufficient for most uses.

The following report shows the first and last days using this day range.

First and Last reliable days
Day	Bible Date	Modern Date	Roman Date	Number
Tue	-137061/9/10 AA	11 Jul -147870 NS	11 Qui 176786 BAUC	AA:-50000000
	-146561/9/10 FE	26 Jul -147867 OS	11 Qui 177539 BC	JD:-52287157
Thu	137062/6/20 AA	24 Mar 125921 NS	24 Aug 126671 AUC	AA:50000000
	127562/6/20 FE	24 Aug 125918 OS	24 Aug 125918 AD	JD:47712843

Another system for counting days is known as the "Julian Day counting system" abrieviated here as the "JD" number. This system is used by astronomers for tracking various astronomical phenomena. It is defined to start at Noon, Grenwich Mean Time, and has a range narrower than the one in use on this sytem. Since its range is to narrow to cover all days since Adam, it is not the prefered day counting system, but, it can be used when Julian Day numbers are known from other sources.

Phil Stone
Updated March 1, 2005

Note: Julian Day Number Epoch is likely off by 1 day. This is a problem for the OS calendar, not the Bible Calendar.