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Astronomers and scientific software use the Julian date today to calculate the number of days between two important events. Many orthodox Christian churches also follow the Julian calendar to celebrate religious days. For example, Christmas in the Julian calendar falls on January 7th.
The start of Julian days, called the start of the Julian era, is defined as noon of January, 1st, 4713 B.C. in the Julian calendar. With this date, all known historical astronomical observations have positive Julian day numbers, so all calculations are simple additions and subtractions.
- Too Many Leap Years
- Skipped Several Days
- Number of Lost Days Varied
- Switch Took More Than 300 Years
- Calendar Chaos
- Double Leap Year
- Many Variations
- Conversion Between Julian and Gregorian Calendars
The Gregorian calendar, also known as the Western or Christian calendar, is the most widely used calendar in the world today. Its predecessor, the Julian calendar, was replaced because it did not correctly reflect the actual time it takes the Earth to circle once around the Sun, known as a tropical year. In the Julian calendar, a leap daywas added ...
Over the centuries since its introduction in 45 BCE, the Julian calendar had gradually drifted away from astronomical events like the vernal equinox and the winter solstice. To make up for this error and get the calendar back in sync with the astronomical seasons, a number of days had to be dropped when the Gregorian calendar was adopted. For examp...
The papal bull issued by Pope Gregory XIII in 1582 decreed that 10 days be skipped when switching to the Gregorian calendar. However, only five countries adopted the new calendar system that year—namely, Italy, Poland, Portugal, Spain, and most of France. Since the discrepancy between the Julian calendar year and the astronomical seasons kept growi...
In total, more than three centuries passed until the Gregorian calendar had been adopted in all countries, from 1582 to 1927. The table below shows when the calendar reform occurred in some countries, including the first and the last.
The delay in switching meant that countries followed different calendar systems for a number of years, resulting in differing leap year rules. In the Gregorian calendar, most years that are evenly divisible by 100 are common years, but they are leap years in the Julian calendar. This meant that the years 1700, 1800, and 1900 were leap years in coun...
The Swedish Empire, roughly comprising the areas of today’s Sweden and Finland, even had a “double” leap year in 1712. Two days were added to February, creating February 30, 1712, after the leap day in 1700 had erroneously been dropped, and the calendar was not synchronized with either the Julian or the Gregorian system. By adding an extra leap day...
In some non-western countries, the calendar reform took on many different guises to accommodate differing cultural and historical contexts. For example, Japan replaced its lunisolar calendar with the Gregorian calendar in January 1873but decided to use the numbered months it had originally used rather than the European names. The Republic of China ...
Currently, the Julian calendar is 13 days behind the Gregorian calendar. So, to convert from the Julian calendar to the Gregorian calendar, add 13 days; to convert in the opposite direction, subtract 13 days. The gap between the two calendar systems will increase to 14 days in the year 2100. Topics: Calendar, History
This difference is 13 days by the 20th century. The calculator below transforms the date from the Gregorian calendar to Julian and vice versa. It's easy to use - enter the date, and it will show Julian and Gregorian calendar dates. Also, there was no Gregorian before 15th October 1582, so you can't tell the date before.
No guidance is provided about conversion of dates before March 5, -500, or after February 29, 2100 (both being Julian dates). For unlisted dates, find the date in the table closest to, but earlier than, the date to be converted. Be sure to use the correct column. If converting from Julian to Gregorian, add the number from the "Difference" column.
Julian dates (abbreviated JD) are simply a continuous count of days and fractions since noon Universal Time on January 1, 4713 BC (on the Julian calendar). Almost 2.5 million days have transpired since this date. Julian dates are widely used as time variables within astronomical software. Typically, a 64-bit floating point (double precision ...
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What is a Julian date?
Why did the Julian Day start on 1st January 4713 BC?
Who invented Julian dates?
How to convert Julian calendar to Gregorian calendar?
The Julian calendar's predecessor, the Roman calendar, was a very complicated lunar calendar, based on the moon phases. It required a group of people to decide when days should be added or removed in order to keep the calendar in sync with the astronomical seasons, marked by equinoxes and solstices.
