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Someone pointed out on a local email list that the ending time for Tish'ah BeAv is listed differently - significantly so - at various institutions in our local community. He noted the following times published:

Large Orthodox A and Large Orthodox B 9:20

Chabad 9:08

Sephardic 8:55

According to the Orthodox Union, none of the above times is even close (within a minute or two) of the Zemanim I would expect:

Tzeis 42 Minutes 9:14 P Tzeis 72 Minutes 9:44 P

The closest is Chabad, which is posting a time 6 minutes earlier than the earliest time listed at the OU. Furthermore, the differences in times seem to only occur on fast days; this year's 9 Av schedule appears, to me, to have the most widely divergent times published here.

What accounts for this disparity? What formula(e) might these organizations be using that they disagree so markedly?

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From Chabad.org, "There are differing opinions when Tzeit Hakochavim takes place. Out of consideration for people's comfort, and considering that the fast days are rabbinic decree, not Torah law, we rely on a slightly earlier opinion concerning the end of day fasts (aside for Yom Kippur)." A and B are probably going by their usual opinion for tzeit hakochavim. – Daniel Jul 15 '13 at 21:28
see myzmanim's explanations of the different times to calculate Tzeit: myzmanim.com/messagebox.aspx?messageid=sources – Menachem Jul 16 '13 at 2:43
How bright are the three stars that you wait for. – Double AA Jul 16 '13 at 3:48
Related: judaism.stackexchange.com/q/3770 – msh210 Jul 16 '13 at 23:46
@Adam I said bright not luminous. – Double AA Jul 18 '13 at 8:40

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