HJD to BJD conversion

Because of the large amount of data published with HJDs only, we created this calculator to convert from HJD to BJD so that they may easily be compared with the superior BJD. This applet will convert from HJD (in either UTC or TT) to BJD_TDB. Due to the approximations inherent to most HJD calculators, this conversion cannot be trusted to better than 1 second. For more precise times, you must retrieve the original JD_UTC and convert it to BJD_TDB using our UTC to BJD calculator.

There is a programmatic interface to this applet. Here is an example that converts a list of HJD_UTCs to BJD_TDB for alpha Centauri. The RA and Dec are always in decimal hours and the FUNCTION can be utc2bjd, bjd2utc or hjd2bjd. It does not support any observatories, so is only accurate to 20 ms.


User inputs are NOT logged

WARNING: BJD_TDB differs from the BJD in Coordinated Universal Time (BJD_UTC) by a systematic 32.184 + N seconds, where N is the number of leap seconds that have elapsed since 1961 (N = 34 as of Jan 1st, 2009). Always specify your time standard and NEVER COMPARE BJD_TDB AND BJD_UTC DIRECTLY.

This calculator should not be used for targets inside the Solar System. We use a plane wave approximation that is only accurate to 1000 seconds for the Moon, 100 seconds for the Main Asteroid Belt and 5 seconds for the Kuiper Belt. Our source code can, however, deal with this and can be run with a demo license of IDL (not tested on Windows).

If you have made use of this calculator (or the source code) in a scientific paper, please cite our paper, which contains a more thorough explanation of the various corrections involved in this calculation.

Copyright © Jason Eastman () All Rights Reserved. Questions, comments, or bug reports welcome.
Last Updated: September 11, 2010