Many of us are familiar with the Old Style (Julian) and New Style (Gregorian) calendars. Birth dates are often given in one of the two calendars, and this may give the impression that unless a person is born in an exotic place or in a particularly strong ethnic environment, we can assume that one of these two calendars are used. Furthermore, we may have the impression that there is a particular date when the New Style calendar is adopted.
Unfortunately, however, the situation is immensely more complex than this, and the consequence of this complexity is that sometimes astrological charts can be incorrect. There are several variations of the Old Style calendar that were used and the New Style calendar was adopted at different times in different countries. In addition to the problem of determining which calendar is in use is the problem of determining if local time is used or if there is a time zone and if daylight saving time is used.
Every year at least a dozen countries change their laws regarding observance of daylight saving time. If you use astrology software that does not have the daylight saving time tables updated yearly, then there is an increased risk that charts you calculate of current events and babies can be incorrect. If the astrology software you use does have tables updated regularly, you should install an update at least once a year to ensure that your daylight saving time tables are accurate.
CALENDAR & TIME CHANCES IN ANCIENT & MODERN TIMES:
The New Style calendar (Gregorian) was adopted in the year 1582 in many parts of western and central Europe, in 1752 in Great Britain and its possessions, in 1753 in Sweden, in the 1800's in Japan, Egypt, and Alaska, and in the early 1900's in several Eastern European countries and the USSR. Turkey began using the New Style calendar in 1926. For example, someone born in Istanbul in the early 1900's most likely has the birth time recorded in the Old Style calendar.
Furthermore, there is no guarantee that birth dates are recorded with the same calendar that is commonly used. We can assume that most people in Turkey in the early 1900's, for example, knew that their calendar was different from that used in most countries, and there is the possibility that government, church, or other official records were sometimes recorded with the New Style calendar. This is reminiscent of the well-known problem of daylight saving time in the USA paticularly in parts of Illinois and Pennsylvania around the 1950's; in some hospitals birth times were recorded in standard time even though daylight saving time was observed. Some hospitals even had two clocks in the delivery room, one with the actual time and the other with the time one hour different which was used to record the birth time.
Adding even more complexity to the problem of determining accurate dates is that through the Middle Ages the year did not necessarily begin on January 1. A common date for the beginning of the year was in the Spring but January 1 was also often used. One authority states that if a Roman document referes to month X, it could possibly refer to 7 different possible time periods! Sometimes two or more systems were used simultaneously, and calendar dates were sometimes distinguished, for example, by being historical, liturgical, or civil.
One example of variations of the Old Style calendar is descrbied by Lois Rodden: “From the 9th to 15th centuries, in some cases as early as the year 1338, various locations of Europe began the first day of the year on 1 May, on 12 August, on 1 November, on 25 December and on 25 March. The most commonly used New Year’s Day was Easter and this calendar was known as the Annunciation Calendar.
Rheims (Reims), France used 25 March as the first day of the year until 1390, after which it named Easter as the New Year day. France, in part, began to use 1 January as New Year day in 1563 by the edict of Charles IX and entirely after 1567.” (http://cura.free.fr/xv/14rodden.html). Rodden cites the book “Book of Calendars” which is edited by Frank Parise.
There are also other calendars such as the Islamic, Jewish, Roman Republican, and Ancient Greek calendar, etc.
If a source gives a date as being in the Old Style calendar, one could ask “which old style calendar?” as there were variations.
Another confusion for dates before the year 1 is the difference between astronomical dates and calendar dates. In our calendar dates there is no year zero. The year preceding 1 AD is 1 BC. In astronomy, however, the year 1 BC is the year zero. For example, the year 100 BC is the astronomical year -99. When looking at ancient dates it is important to be aware of this distinction.
To summarize, there are many variations of calendars, and sometimes uncertainty as to what calendar was used for recording birth times or even what calendar was in use in a particular place at a particular time.
A simple designation of “Old Style calendar” is ambiguous because there are variations of the Old Style calendar that were used. A reasonable way to resolve some of this confusion is to always use New Style calendar dates and in notes regarding the birth data include information about what the calendar in use was at the time and how the date was recorded.
The fact that people born in the early 20th century are born with the Old Style calendar in use and that many countries, or parts of countries, change the dates when daylight saving time is observed every year are additional issues that astrologers need to be aware of. A difference in one hour will change the rising sign about half the time so this is an important issue.