HistoryCal - Definition
jdn# Julian Day Number

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Calendar Description

The Julian Day Number calendar is a simple count of days and is the system used internally by HistoryCal. It is closely related to the Julian Day (or Julian Astronomical Days) but the time element is missing and the day is considered to start at midnight.

Note that the terms "Julian Day Number", "Julian Day" and "Julian Astronomical Day" are often used interchangeably in the academic world. However, this project will use the term "Julian Day Number" (signature jdn) to describe the above definition of the calendar and the term "Julian Day" (signature jd) to describe the more common academic definition, where the day begins at midday. Thus:-
jdnday
x
=
jdday
x - 0.5
.

Use Case

There is no known historical use of calendar, although the Julian Day scheme, on which it is based, has been in use by the scientific community, particularly astronomers, for many years. Its main purpose is as the intermediate and standard date value used internally by the HistoryCal program. It may also be used as the base for other day count calendar types. It is also used to input date values in a HistoryCal script.

Definition

Record
day

Since the Julian Day Number calendar is the same as the internal Cal library calendar, the definition is trivial. Days start at midnight.

The Record consists of a single Field named day.

The Epoch is the same as the internal version, so
jdnday
1
=
jdnday
1
.

Script

Default Script
grammar d { alias field { Day, day; } alias stylename { Day, ddddd; } format d, "(Day)"; pref d; } scheme jdn { name "Julian Day Number"; base jdn; grammar d; }

Although this calendar has no historical uses, it is included in the default script because it is used as the intermediate form when converting between other calendars. It may also be used to derive other day count calendars.

The script has no dependencies.


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19th January 2014