Re: BJD to HJD and UTC conversion

Posted by karenacollins on Jan 09, 2025; 7:09am
URL: http://astroimagej.170.s1.nabble.com/BJD-to-HJD-and-UTC-conversion-tp2614p2629.html

Hi Christophe,

The add astronomical data to table process you described is correct.

The roughly ~66 second offset between BJD_TDB and HJD_UTC is about right (depending on the date of the TESS observations). The offset is a combination of 32.184 seconds plus N leap seconds since 1961 (which is currently 37 - you may need to click "Update" in MP Coordinate Converter panel to get the most recent values), plus up to the ~+/-8 seconds of offset of the heliocenter to the barycenter. See Jason Eastman's converter page and the reference to his paper there-in.

However, note that for TESS data time stamp conversions within AIJ, there will be an inaccuracy of up to +/-1.3 seconds because BJD calculations in AIJ assume the observer is at an observatory on the surface of the Earth, so we not account for the position of the TESS spacecraft in it's orbit. Since HJD is not a very accurate way to report astronomical timings, I doubt the residual error from the AIJ calculations will be important.

Karen