|
|
|
|
|
|
|
leap year or other intercalations are often complex and may lie in the realm of observation, not calculation. |
|
|
|
|
|
|
|
|
In general, the application of mathematical operations to dates expressed in terms of cyclical units such as days, months, and years is a misapplication of rules that assume constant relationships between successive units. Some examples of the problems encountered with this general scheme are showcased in the test program DTLT_179.C. |
|
|
|
|
|
|
|
|
If, on the other hand, you were to measure both elapsed and event time using a single unit, then mathematical operations could easily produce consistent results. |
|
|
|
|
|
|
|
|
We could agree to meet for lunch in 1,340 seconds, for example, and we could agree to meet in Berlin for the convention at 212,198,411,300 seconds, not 212,198,324,900, as previously planned. In this second example, we have simply adopted an arbitrary zero point and count forward or backward in seconds from that point as a calendar system. |
|
|
|
|
|
|
|
|
This is a logical system, but humans are not comfortable thinking in these terms. For the purposes of computer calculation, however, you can see that one single linear time scale does express our culture's concept of time. Moreover, it allows you to perform calculations very easily. |
|
|
|
|
|
|
|
|
You can have the best of both worlds, then, by continuing to use the traditional calendars, with which you are psychologically comfortable. Computer technology can quickly translate these traditional systems to a linear scale and back again when you want to perform calculations or relate two traditional systems to each other. |
|
|
|
|
|
|
|
|
Note that having a single linear time scale allows you to convert dates in any particular calendar system to the time scale, perform your calculations using simple math on the linear time scale, and convert the result back to the particular calendar system. |
|
|
|
|
|
|
|
|
Furthermore, you can easily convert different calendar systems in the same way, by simply converting the linear time to a calendar system other than the one with which you started. To convert a date in calendar X to its equivalent in calendar Y, you convert the X date to linear time, then convert linear time to an equivalent date in calendar Y. |
|
|
|
|
|
|
|
|
2.5.2
The Julian Day Number |
|
|
|
|
|
|
|
|
Such a linear system for dealing with time exists already and has been used by astronomers for years. It is called the Julian Day number. In this book, I will use it as the basis for all calculations. |
|
|
|
|
|
|
|
|
For many years, different societies used different calendars for marking events. Many of them counted years from some initial epoch, whereas others constantly started over with each reigning monarch in a system called "regnal years." |
|
|
|
|
|