What is Julian Date?
The International Astronomical Union unites many astronomical societies from around the world under its roof. This union, which is a member of the International Science Council, is the official institution of the astronomical community.
The Julian calendar, originally called the “Radical Calendar“, is a calendar that was used by several ancient cultures, from the middle of the second millennium BC until the first century BC. However technically, a today’s julian date can mean different things.
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Julian Calendar 2025
The Julian calendar for 2025, like its predecessor introduced by Julius Caesar in 46 BC, treats 2025 as a leap year, adding an extra day to February. This calendar follows a simpler leap year system than the Gregorian calendar, designating every fourth year as a leap year without the more complex exceptions found in the Gregorian system, such as skipping centurial years not divisible by 400.
In 2025, the Julian year begins on a Saturday and ends on a Sunday, making it a year with 52 full weeks and one extra day. This additional day brings February’s total to 29 days. The remaining months follow the standard pattern of alternating between 30 and 31 days, with July and August being the only consecutive months with 31 days each.
The difference between the Julian and Gregorian calendars grows over time due to their varying leap year rules. By 2025, this discrepancy will be 13 days. For example, when it’s January 1, 2025, in the Gregorian calendar, it will correspond to December 19, 2024, in the Julian calendar.
Some Orthodox Christian churches continue to follow the Julian calendar, which results in different dates for religious observances compared to those using the Gregorian calendar. For instance, Christmas is celebrated on January 7 in the Julian calendar, aligning with December 25 in the Gregorian calendar.
The Julian calendar does not accommodate daylight saving time adjustments. Therefore, regions adhering to this calendar do not change their clocks in 2025.
Despite its simplicity and regular month and leap year pattern, the Julian calendar’s less accurate accounting of the solar year means it gradually drifts out of alignment with the astronomical seasons. Nonetheless, it remains significant for historical studies, religious observances, and in astronomy, particularly through its influence on the Julian Day Number system, which provides a continuous count of days for astronomical calculations.
Today’s Julian Date
Today's date is 19-05-2025. Today's Julian Date is 2460815.Julian Date Converter
Julian Day, a time measurement system, is included in the Julian date system. The Julian Day proposed by the International Astronomical Union for use in astronomical studies, BC. Presents the time interval of a day in fractions of days starting from January 1, 4713.
How is Julian Date Calculated?
Julian Day, BC. It presents the time interval of a day starting from Noon with Universal Time (UT) on Monday, January 1, 4713, in fractions of the day and the day. In other words, noon was chosen as the starting time of the day. The first day is considered to be the 0. Julian Day. In this way, the multiples of 7 always correspond to Monday.
Negative values can also be used, but these values invalidate any history saved. While each day is expressed as an integer, any hour of the day is added to this integer as a fraction of the day. The date January 1, 4713 is the beginning. The days that come after this date have been counted consecutively and added to this number. These numbers are indicated in the astronomy annals as charts by years, months, and days. The Julian Date, abbreviated as JT, is the date determined by these numbers. The Julian Date of any date can be found in 2 ways:
The charts in the astronomy annals are checked.
The Julian Day calculation formula is used.
The formula for calculating the Julian Day is as follows:
JT = 2415020 + 365 x (year – 1900) + N + L – 0.5
This formula; It gives the Julian Date that coincides with any date since 1990. Universal time is EZ = 0 in this calculation. N is the number of days after the new year, and L is the number of leap years between 1901 and the date to be calculated. In the formula; 2415020 refers to the Julian Day corresponding to January 1, 1900, and the amount 0.5 denotes the decimal equivalent of the half day resulting from the start of the Julian Day in the middle of the day.
The formula for finding the number N is as follows:
N = <275M / 9> -2 <(M + 9) / 12> + I-30
In this formula, M is the number of months, and I is the day of the month. Also <> indicates that the full part of the number in the brackets will be taken. For a leap year, the factor of 2 in the 2nd term is removed.
Correspondence of the decimal parts of Julian Date in hours, minutes and seconds:
0.1 = 2.4 hours or 144 minutes or 8640 seconds
0.01 = 0.24 hours or 14.4 minutes or 864 seconds
0.001 = 0.024 hours or 1.44 minutes or 86.4 seconds
0.0001 = 0.0024 hours or 0.144 minutes or 8.64 seconds
0.00001 = 0.00024 hours or 0.0144 minutes or 0.864 seconds.
Julian Calendar
The Julian Calendar is the most famous of the solar calendars. B.C. It was prepared by the Roman Emperor Jules Caesar (Jules Ceasar) in 46 BC and was used in the western world until the 16th century. It is also known as the Julius Calendar. It is considered to be the first version of the Gregorian calendar.
Aiming to solve the confusion and problems in the calendars used in the past years, Caesar received help from the Alexandrian astronomer Sosigenes. With the suggestion of Sosigenes, this calendar was prepared based on the movements of the sun, not the moon. Aiming to correct seasonal shifts, Sosigenes calculated a year as 356.25 days.
In this way, while the years that cannot be divided into 4 are 365 days, the increasing quarter days from these years were added to the 4th year and the leap year was increased to 366 days. In order for 1 year to be 12 months, leap years are arranged to be 6 months 30 days, and the other 6 months 31 days. In non-residual years, 1 day is removed from the last month of the year.
At that time, New Year’s Eve was in March. Therefore, February, which is the last month of the year, has been reduced to 30 days in leap years and 29 days in other years. Caesar wanted to immortalize his name as the organizer of the calendar and changed the name of July to July.
The arrangements made in the calendar after the death of Caesar could not be implemented properly. The fact that Pontifeksler, who made arrangements in the calendar, made a leap year application in 3 years, caused confusion again.
During the 40 years of application in this way, there has been 3 days of slippage. Roman Emperor Augustus, BC. In the 8th year, it corrected this shift by stopping the leap year application for 12 years. He also changed the name of August to his own name, Augustus. In the regulations made; It was taken 1 day from February, and added to August, after July 31 and August took 30 days. In this way, February took 29 days in leap years and 28 days in other years. Julian Calendar, BC. It was used from the 46th to the 16th century.
Leap year practice was applied in Julian Calendar for the first time in history. As a result of a small difference in this calculation, a 1-day shift occurred approximately every 128 years. Due to the confusion created by this shift, the Julian Calendar was abandoned in the 16th century and the Gregorian Calendar was adopted.
Understanding the Differences between the Julian and Gregorian Calendars
The calendar is a crucial tool in our daily lives, helping us to organize time and plan our schedules. However, did you know that there are actually two different calendars in use today? The Julian calendar and the Gregorian calendar are the two most widely used calendar systems in the world, and while they may seem similar at first glance, there are some key differences between the two.
The Julian Calendar
The Julian calendar was first introduced by Julius Caesar in 45 BC as a way to align the Roman calendar with the solar year. The calendar was based on a year of 365 days, with an extra day added every four years to account for the extra time it takes the Earth to orbit the Sun. This extra day was added to February, creating what is known as a “leap year.”
One of the main features of the Julian calendar is its simplicity. With only one rule to remember (a leap year every four years), it was easy for people to use and understand. However, the Julian calendar’s approximation of 365.25 days for the tropical year (the time from one spring equinox to the next) was slightly too long. As time passed, the excess (11 minutes and some 14 seconds according to modern measurements) slowly added up, causing the calendar date of the equinox to move ever earlier (by one day every 128 years or so).
The Gregorian Calendar
To correct the problem with the Julian calendar, Pope Gregory XIII introduced the Gregorian calendar in 1582. The new calendar was based on the same principles as the Julian calendar, but with a few key changes. The most significant change was the introduction of a new rule for leap years. In the Gregorian calendar, a leap year is still added every four years, but years that are divisible by 100 are not leap years unless they are also divisible by 400. This means that the year 2000 was a leap year, but the year 1700 was not.
The introduction of this new rule has helped to keep the calendar more closely aligned with the solar year. In fact, the Gregorian calendar is accurate to within just 26 seconds per year. This means that the calendar will not need to be corrected for over 3,000 years.
One of the most significant differences between the Julian and Gregorian calendars is that the latter is in use today by most of the world. The Catholic Church and many Catholic countries adopted the Gregorian calendar immediately, while other countries followed suit over the next several centuries. However, some countries, such as Greece and Russia, did not adopt the Gregorian calendar until much later.
FAQs
Which calendar is more accurate?
The Gregorian calendar is more accurate than the Julian calendar.
When was the Julian calendar introduced?
The Julian calendar was introduced by Julius Caesar in 45 BC.
When was the Gregorian calendar introduced?
The Gregorian calendar was introduced by Pope Gregory XIII in 1582.
Which countries still use the Julian calendar?
Some countries, such as Greece and Russia, did not adopt the Gregorian calendar until the early 20th century.
How often is a leap year in the Julian calendar?
In the Julian calendar, a leap year is added every four years.
How often is a leap year in the Gregorian calendar?
In the Gregorian calendar, a leap year is added every four years, but years that are divisible by 100 are not leap years unless they are also divisible by 400.