Measuring Days

Issues on measuring days when a day is given prophetically.


Ask someone what day it is and the answer will usually come back "Tuesday" or some other day of the week. Ask again and the answer will usually be the date within the current month. Ask a third time and the answer will usually be a formal answer with a day, month and a year. Each of these answers are different ways of describing the current day.

Of course people use other systems for time measurement: hours, minutes and seconds, when time within a day is important, but for measuring longer periods of time the basic unit for all such measurements is a single day.

The most fundamental of all days, at least for most people, most of the time is "today" the day currently going on. Today, for example, you are reading about time. If you are like most people you started the day with a rough plan of the things you intended to do today. When the day completes you’ll look back at the things you did today and, perhaps, plan what you intended to do "tomorrow."

In the English language two other words augment "today." Those words are "yesterday" and "tomorrow." Together the three words are all that are needed to describe daily time, since together these words can be used to describe the cyclic, or chained, nature of days. As everyone understands days follow each other in sequence, just as they have for as long as anyone can remember.

Limits on Today, Yesterday and Tomorrow

These three words are awkward when the subject of conversation is beyond immediate time. The historical solution to this problem is the use of a calendar, a system for bunching days into convenient units. Calendars have their own set of strengths and weaknesses, which we’ll get to shortly. Fundamentally, though, the problem of dealing with time beyond yesterday, today and tomorrow, is to use math of some sort in order to count out days.

Imagine for a moment using the number 0 for "today", -1 for yesterday and 1 for tomorrow. Unlike the English language words, this day-counting system can be extended to any number days past or future. Day -2 is simply the day before yesterday. Day -3 is the day before the day before yesterday, and so on. Similarly, Day 2 is the day after tomorrow, and so on.

Though it does not lend itself to human mental processes, it is easy to see how day 950 on this scheme could easily be know. In fact for all days possible, even back to the formation of planet Earth, even for as long as it should endure, each day is easily identifiable using this scheme.

The only problem, of course, is that come tomorrow, anyone using such a scheme would want to renumber every day so that day 0 would shift up by 1 day. This is awkward since documentation from "today", day 0, would be out of date "tomorrow" when it became day 0. To avoid such a problem day 0 needs to be fixed at some point in historical time on some specific day. Then all other days, following the yesterday, today and tomorrow chain up from that day 0 lands on some arbitrary day number. Today is thus not going to be day 0, but some other arbitrary day number, so many days away from day 0.

It is possible for anyone to set up such a day-counting system, should there be a good reason. The Bible Time project includes exactly such a system, for reasons we’ll explore later. But, since the value of such a system is in comparing calculations with others, it would be best to use a standard already defined. There is one, it is called the "Julian Day Counting" system.

Julian Day Counting

Introduced in... it sets day 0 at .... Pick up an almanac or use cross calendar software on a computer and the Julian day number for any given day can be computed.

Why is this important?

Day numbers, backward and forward from today, provide a fundamental and accurate way of measuring time. By selecting a standard day 0 and by tracking "today" against that standard we can always accurately identify days, past or future, from today.

Day numbering systems are as accurate as days themselves, it only breaks down on fundamentally curious days such as the day in Hezekiah’s time when the sun went back 10 steps or in Joshua’s time when the sun stood still for 1/2 a day.

In both of these two special cases there is no report of anything or anyone falling down. This suggests the angular momentum of planet earth was not changed at all on either of these occasions. Likely what changed was the angle of the rotational pole relative to the orbit of the earth around the sun. So, even here a day is a fundamental until of time that easily copes with such odd phenomena.

The Bible’s prophetic time system also appears to be given accurately to individual days. The only way this precision can be seen is by using a time measurement system that is also accurate to individual days. Calendar based time, though usually accurate to the day is not always this accurate. Calendar based time is not usually accurate enough for measuring prophetic time.

Days of the week

When pressed with the question, "what day is it?" people usually answer with the day of the week. The weekly cycle of days provides a context for understanding daily time. The context is only mildly larger than yesterday, today and tomorrow. The day of the week provides a convenient framework for understanding time.

In most national languages the days of the week are typically named instead of numbered, though some day names are their numbers. This technique, that also occurs with month names, appears as a way to help illiterate citizens track which day it is. Even without the ability to count, people can have an innate sense of the day.

Since at least the time of the Exodus from Egypt people have been grouping days into weeks. In the modern world there are two different systems for identifying when the week cycles. In the Jewish and American system the week ends after Saturday, while in the European system the week ends after Sunday. Calendars printed for use in Europe typically follow the European standard while calendars printed for use in the United States typically follow the older Jewish standard. To avoid confusion we will always be referring to the day-of-the-week by name, not by number.

Except for a period during the French Revolution, when there was an attempt to change the week length from 7 to 10 days, there have been no known changes to the weekly cycle of days anywhere in history. (Though, of course, the week has not been know to all people groups nor observed in all places.)

The day of the week for any specific day-numbered day can be found by looking at the remainder when the day number is divided by 7. For computer literate readers this is called a modulus. Each of the possible remainders, 0 through 6, uniquely identifies a particular day of the week.

Any day in history with the same remainder after being divided by 7 falls on the same day of the week as any other day with the same remainder.


Day numbering, as introduced here already, is not how the world generally identifies individual days. The public at large typically uses some sort of calendar. Calendars are specific systems for bunching days into months and years. Some calendars, like the Chinese calendar, bunch years into still larger units. For most people today, though, the calendar is simply the system for grouping days into years.

Unlike days and weeks, the fundamental units of months and years are not fixed quantities. Different cultures at different times have chosen different ways to group days into months and months into years. This is fundamentally why calendars are unable to accurately measure time across all of history.

Modern Calendar

Properly speaking the Julian Calendar was introduced by Julius Caesar in 45 BC. This followed 46 BC, a year of correction, which was also the result of Julius’ actions. That said, the calendar went through further revision by Augustus Caesar introduced in 8 BC which is the first year with a calendar shape identical to the modern Julian Calendar. By this measure it should be called the Augustus Calendar. This was not the end of revisions, though, that lead to the current Julian calendar.

Very early in Church history the date for New Years was shifted from the pagan, Roman, definition of January 1, to March 25. This was apparently a reflection of the early church belief that Jesus’ was raised from the dead on Sunday March 25, 31 AD. We discuss this entire topic as part of our Life section.

This change to March 25 was done for religious reasons, but it "stuck" in the governments of various western nations and became the common calendar. When England, and her colonies, eventually switched to the modern Gregorian calendar New Years day was shifted back to the pagan date of January 1.

Having New Years Day fall in the middle of a month brings havoc with many of the calendar conventions that we are used to. Consider that expressions like "Last June" implicitly imply the year. But, under the Julian calendar with New Years on March 25, expressions like "March, 1701" are now hard to decipher. March 25 through 31 fell at the start of 1701, while March 1 through 24 fell at the end.

The following is the structure of Julian calendar used from the start of the Christian era until it was supplanted by the Gregorian Calendar.

Number Name Abbr. Common Leap
1 March Mar 7 7
2 April Apr 30 30
3 May May 31 31
4 June Jun 30 30
5 July Jul 31 31
6 August Aug 31 31
7 September Sep 30 30
8 October Oct 31 31
9 November Nov 30 30
10 December Dec 31 31
11 January Jan 31 31
12 February Feb 28 29
13 March Mar 24 24
Totals: 365 366


With this sort of odd mapping of March into two different places in the annual calendar I would suspect that month numbers were almost never used. The previous table shows why. The 12 months common to the year are spread across 13 slots.

Even though this may seem strange to modern readers, consider this was the common calendar for the better part of 1700 years. If you had grown up with it you would have thought nothing of it.