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Julian day calculator

World's simplest time tool

With this browser-based application, you can calculate the Julian day (JD) and the Julian day number (JDN) for any date in the Gregorian calendar (modern calendar) or Julian calendar (old calendar). You can enter multiple dates in the input field, choose the calendar type, and get the JD and JDN for each of the dates as the output. You can also specify the dates with an exact clock time and adjust the decimal precision of the output JDs. Created by computer nerds from team Browserling.
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Input Calendar
Calculate the Julian day for Gregorian calendar dates.
Calculate the Julian day for Julian calendar dates.
Julian Day Precision
Adjust the precision of a JD.
To calculate a JDN (Julian day number), enter the precision of "0". This will round a JD in the right direction to produce a whole number, which is a JDN.
Julian day calculator tool What is a julian day calculator?
This is a quick online utility for converting a Gregorian date or a Julian date to a Julian day. The Julian day (denoted as JD) is a unit of time in the Julian dating system and it's the number of days that have passed since the beginning of the Julian period, which started on noon (12:00:00) on January 1, 4713 BC (in the Julian calendar). This same date is equal to equal to noon (12:00:00) on November 24, 4714 BC in the Gregorian calendar. The Julian day continuously increases and has a fractional time part. For example, today on "2022-05-12 10am", when we're publishing this tool, the JD is equal to 2459711.917. The Julian day number (denoted as JDN) is an integer number assigned to the whole solar day. In this same example, it's 2459712 (because the day number is assigned to each day and is calculated by rounding the JD). Our program allows you to calculate the JD and JDN for a date from both calendars (Gregorian and Julian). For example, if you have a modern calendar date, then select the Gregorian calendar mode in the options. If you want to find a JD or JDN for an ancient calendar date, then switch the conversion mode to the Julian calendar. To find JDs for multiple dates, enter all the dates, one per line. The dates can be entered in the format "YYYY-MM-DD" and you can also add a time part to them as "YYYY-MM-DD hh:mm:ss". When you add a time part, the Julian day may become a decimal number. In this case, can specify the rounding precision of the Julian day using the precision option. To get a Julian day number (JDN), enter precision "0" as this precision will correctly round a JD so that it becomes an integer. Timeabulous!
Julian day calculator examples Click to use
Julian Day of the First Tweet
In this example, we convert the Twitter launch date to a Julian day. The first message on Twitter was posted on March 21, 2006, at 12:50 pm. We enter this date and time into the input, set the Julian day precision equal to 5 digits, and get JD = 2453816.03472 as the output.
2006-03-21 12:50
2453816.03472
Required options
These options will be used automatically if you select this example.
Calculate the Julian day for Gregorian calendar dates.
Adjust the precision of a JD.
Julian Date to Julian Day
This example converts two Julian calendar dates to Julian days. The first date "-4712-01-01 12:00:00" is the start date of the Julian period – it's the first Julian day with the JD count equal to 0. The second date "1582-10-04 23:59:59" is the last date of the Julian calendar (the next day, people switched to the more precise Gregorian calendar).
-4712-01-01 12:00:00 1582-10-04 23:59:59
0 2299160.5
Required options
These options will be used automatically if you select this example.
Calculate the Julian day for Julian calendar dates.
Adjust the precision of a JD.
First Space Flights
In this example, we load the first five calendar dates of space travelers. The first flight into the space was made by Yuri Gagarin on April 12, 1961 (JD = 2437401.5), followed by Alan Bartlett Shepard Jr. on May 5, 1961 (JD = 2437424.5), followed by other astronauts.
1961-04-12 1961-05-05 1961-07-21 1961-08-06 1962-02-20
2437401.5 2437424.5 2437501.5 2437517.5 2437715.5
Required options
These options will be used automatically if you select this example.
Calculate the Julian day for Gregorian calendar dates.
Adjust the precision of a JD.
Pro tips Master online time tools
You can pass input to this tool via ?input query argument and it will automatically compute output. Here's how to type it in your browser's address bar. Click to try!
https://onlinetimetools.com/convert-date-to-julian-day?input=2006-03-21%2012%3A50&from-gregorian-date=true&julian-day-precision=5
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