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.

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 0. The following is the report:

January 1, -4713 OS is the defined starting epoch, day 0, on the JDN system, in agreement with other online JDN number calculators. Auditing this aspect of the Auditable Date Report.

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:

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 time line 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 -2,000,000,000 <= DayNumber <= 2,000,000,000. This is sufficient for most uses.

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

By Phil Stone
Revised 12999-10-01 (2008-09-24)