British Astronomical Association
Supporting amateur astronomers since 1890

Secondary menu

Main menu

Home Forums Computing
Terms of use

JD to BJD convertion

4 posts / 0 new
Last post
John Mallett's picture
Last seen: 4 days 20 hours ago
Joined: 26/11/2016 - 14:41
JD to BJD convertion


It would be really great if someone has an executable file that would convert JD to BJD without being online.

In fact if someone had a java or PHP application that I could try to rewrite as an exe that might be a route.

I am collecting very short period data and need to see if the period is shifting or varying.  HJD seems not to be accurate enough.

Any help would be great.


Roy Hughes's picture
Last seen: 18 hours 41 sec ago
Joined: 04/03/2014 - 12:54
A google search for BJD date

A google search for BJD date found

This in turn leads on to 'source' (at foot of the page). Maybe this would help.

Sorry, I don't understand a word of it but it may mean somthing to you.


Americo Watkins's picture
Last seen: 5 hours 48 min ago
Joined: 11/03/2014 - 13:12
Hi John,

Hi John,

the free software AstroImageJ;

  ( )

does have a facility within it's  DP converter page that provides BJD time either on board or tick a box and it supplies the time from the uni of Ohio site mentioned on other earlier reply.  Some useful instructions and manual provided by Denis Conti at;

However, the accuracy is to 5 dp and 6 respectively and you will have to set the DP converter to your site and target's RA and DEC and be sure to always update the leap second tab before use.

Regards,  Eric

nickjames's picture
Last seen: 6 hours 33 min ago
Joined: 12/10/2013 - 18:16
The GPL Positional Astronomy

The GPL Positional Astronomy Library (PAL) can be found on Github here. It is an open-source reworking of Patrick Wallace's slalib and it contains all the functions you need to do this. Alternatively the original slalib in Fortran is GPL and should be available somewhere. Even if you can't use these functions directly they are a good source of information on how to do the conversion accurately.