Supported Eras

On all pages where "historical" dates are handled (typically all those related to the Event and Title objects -- see below), you will now be asked to select the era used to express that date.

The eras currently supported by the Hirtius application are:

Julian Era
Gregorian Era
Transitional Era

Please note: All other (non-historical) date fields present in the application are treated as Gregorian.

Julian Era

The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year (without exception). The Julian calendar was proposed in 46 BC by Julius Caesar, as a reform of the earlier Roman republican calendar, which was largely a lunisolar one. It took effect on January 1st, 45 BC (source: Wikipedia -- see Bibliography).

Gregorian Era

The Gregorian calendar went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day 'tropical' or 'solar' year that is determined by the Earth's revolution around the Sun (source: Wikipedia -- see Bibliography).

The algorithm as currently implemented in Hirtius supports Gregorian dates up until Dec. 31, 2499.

Transitional Era

This is not properly speaking an era, and it can't be assigned to dates related to events. It is used on the Calendar View page to display the unusual calendar of those years during which occurred the transition between Julian and Gregorian era.

The table below lists the transition dates known to the Hirtius application and the geographical zones where they apply:

Sphere of influence	The day that followed...	Was...
Italy / Spain(¹)	October 4, 1582	October 15, 1582
France	December 9, 1582	December 20, 1582
Netherlands(²)	December 14, 1582(³)	December 25, 1582
South Netherlands(⁴)	December 21, 1582(³)	January 1, 1583
Prov. of Holland	January 1, 1583(³)	January 12, 1583
Germany [catholic]	December 21, 1583	January 1, 1584
Prussia	August 22, 1612	September 2, 1612
Germany [reformist](⁵)	February 18, 1700	March 1, 1700
United Kingdom(⁶)	September 2, 1752	September 14, 1752
Sweden	February 17, 1753	March 1, 1753
Bulgaria	March 31, 1916	April 14, 1916
Soviet Union	January 31, 1918	February 14, 1918
Greece	February 15, 1923	March 1, 1923

Notes:

Also Portugal, Polish-Lithuanian Commonwealth, Papal States
Provinces of Brabant, Zeeland and States General
Start date self computed
Modern Belgium, except Duchy of Brabant
Also Denmark, Norway
Also part of modern United States

Please keep in mind that this list is not exhaustive by any means, but new transition dates can easily be added if needed.

Historical vs Regular dates in Hirtius

"Regular" dates in Hirtius are those that are used to store date information supposed to be more or less contemporary with the user of the application (for instance the date a picture was shot) or internal application events (such as the creation or last modification of an object).

When entered by the user, regular dates use the ISO format 'YYYY-MM-DD' and are represented internally by the 'DATE' or 'DATETIME' MySQL/MariaDB data types. According to the DB server documentation, their supported range goes from '1000-01-01' to '9999-12-31' which, although suitable to the purpose stated above, clearly falls short when it comes to representing historical dates.

As a result, Hirtius implemented its own data type to store "historical" dates, i.e. those a user might enter to document an historical event. Historical dates are entered using the following format: '(-)YYYY/MM/DD' (which already differentiates them from the "regular" dates). But in addition to this textual representation, they are also stored in the database as Julian Day Number (JDN) -- more on this below. The advantages of this representation is that it allows for:

easy chronological sorting of events
easy computation of elapsed time between them
calendar independance (JDN can be converted back to Julian or Gregorian calendar as needed)

Julian Day Number

The Julian day is the continuous count of days since the beginning of the Julian period, and is used primarily by astronomers, and in software for easily calculating elapsed days between two events. The Julian period is a chronological interval of 7980 years; year 1 of the Julian Period was 4713 BC. The Julian day number (JDN) is the integer assigned to a whole solar day in the Julian day count starting from noon Universal Time, with Julian day number 0 assigned to the day starting at noon on Monday, January 1, 4713 BC, proleptic Julian calendar, a date chosen so as to preceed any dates in recorded history (source: Wikipedia -- see Bibliography).

In Hirtius database, JDN are coded as 'int(11)', meaning that they have a theoretical range going from -2147483648 to 2147483647. As such, its scope is much wider than really needed for historical purposes.

Also note: Even though the Julian Day numbering system allows for decimal values to be used in order to accurately refer to a specific time inside a given Julian day, Hirtius (as stated above) codes them using integer values, which means that an entire day is its limit in terms of accuracy (which was deemed sufficient for most historical research purposes). But this also means that you should expect off-by-one errors when comparing dates on either side of the date line.