I think the reason for the

Forums Computing Heliocentric Julian date I think the reason for the

Nick James

I think the reason for the difference is that the two values of JD that you calculated are in different timescales. I assume that the BAA calculator calculates HJD in the UTC timescale whereas the Ohio site calculates it in TDB. At present TDB is around 68.2s ahead of UTC so a BJD(TDB) will be around 68s later than HJD(UTC). When talking about JD it is important to specify the timescale used. The difference between the Ohio and BAA times is 68.44s which agrees well.