Re: Apparent discrepancy in BJD
Posted by karenacollins on Mar 22, 2018; 2:15am
URL: http://astroimagej.170.s1.nabble.com/Apparent-discrepancy-in-BJD-tp982p983.html
Hi David,
I did a quick search and didn't spot an ISU JD_UTC to BJD_TDB converter, but maybe you are referring to the OSU one here:
http://astroutils.astronomy.ohio-state.edu/time/
If that is the case, the OSU website is more accurate than AIJ. However, the largest difference I have seen is about 0.2 seconds. Before digging deeper, please confirm that you have an up-to-date leap second table to clicking the "Update" button circled below in the MP coordinate converter panel, and then re-running the calculations. If it is still off by more than a few hundredths of a second, let me know.
I will also note that if you want the ultimate precision, AIJ can also extract the times from the OSU website, but that takes longer. To do that check the "OSU/Internal" option circled below.
Karen
URL: http://astroimagej.170.s1.nabble.com/Apparent-discrepancy-in-BJD-tp982p983.html
Hi David,
I did a quick search and didn't spot an ISU JD_UTC to BJD_TDB converter, but maybe you are referring to the OSU one here:
http://astroutils.astronomy.ohio-state.edu/time/
If that is the case, the OSU website is more accurate than AIJ. However, the largest difference I have seen is about 0.2 seconds. Before digging deeper, please confirm that you have an up-to-date leap second table to clicking the "Update" button circled below in the MP coordinate converter panel, and then re-running the calculations. If it is still off by more than a few hundredths of a second, let me know.
I will also note that if you want the ultimate precision, AIJ can also extract the times from the OSU website, but that takes longer. To do that check the "OSU/Internal" option circled below.
Karen
On 3/21/2018 12:05 PM, Davidgp [via AstroImageJ] wrote:
I am new to AIJ and from answers on this website I have been able to insert into the Measurement Table, BJD times in the format BJD_TDB_MOBS. Previously I had always used the Iowa State University (ISU) website for converting from JD_UTC to BJD_TDB and so decided to cross check. In doing so I get a difference of ~1.89s +/-0.03s taken over 61 observations. I used the same Simbad coordinates for V*NY Vir (RA 13:38:48.15; Dec -02:01:49.1) in both MP Coordinate Converter and the ISU webpage. Likewise I used the same observatory coordinates (Long -110:23:53.18; Lat +31:39:56.08) for both with altitude set to zero for both. Exposure time was 15s. I am unable to find the cause of this difference but wondered if it was related to the definition of BJD_TDB_MOBS. As an example I get 2458190.882506 and 2458190.882483 for ISU and AIJ respectively.
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