Milwaukee Astronomical Society


Julian Day Conversion

Many astronomical observations require that the data be presented with Julian Dates.

The Julian Day is a consecutive day count starting on January 1 of the year -4712 (= 4713 B.C.E.).

In the past observers calculated this date based on yearly charts. You can still get them from the AAVSO.

An Easier Way to Calculate JD:

Though you can calculate the JD yourself, we highly recommend you use a calculation tool. We offer you a Calendar to JD form here taken from the AAVSO site here. There they also have a JD to Calendar option as well as a thorough explanation about the Julian Dates and an explanation about Julian Dates and why they are so important

To convert from UT to JD enter the time in UT:

Year Month Day
Hour Min Sec

The answer will appear in a new window from a AAVSO page. You can simply close that window after you get the answer.