Note:The historic and non-halakhic information in ths article was added by Arutz Sheva
This year, Tuesday, December 14th, is the Fast of the 10th of Tevet, Asarah B’Tevet, on the Hebrew Calendar.
On Asarah B’Tevet in the year 3336, Nevuchadnetzar, king of Babylonia, laid siege to Yerushalayim, marking the beginning of the events that led to the destruction of the First Temple, the exile of the People of Israel from their land and soon after, the last vestiges of self rule for those who remained. The story is recounted at the end of the Book of Kings, Chap. 25:
"So in the ninth year of Zedekiah’s reign, on the tenth day of the tenth month, Nebuchadnezzar king of Babylon marched against Jerusalem with his whole army. He encamped outside the city and built siege works all around it. The city was kept under siege until the eleventh year of King Zedekiah. By the ninth day of the fourth month the famine in the city had become so severe that there was no food for the people to eat.
"Then the city wall was broken through... They killed the sons of Zedekiah before his eyes. Then they put out his eyes, bound him with bronze shackles and took him to Babylon. On the seventh day of the fifth month, in the nineteenth year of Nebuchadnezzar king of Babylon, Nebuzaradan commander of the imperial guard, an official of the king of Babylon...set fire to the Temple of the Lord...carried into exile the people who remained in the city, along with the rest of the populace and those who had deserted to the king of Babylon. But the commander left behind some of the poorest people of the land to work the vineyards and fields."
To commemorate the tragic day when the siege began, the Nevi’im (Prophets) instituted the ta’anit tzibbur (communal fast day) of Asarah B’Tevet.
In addition to the 10th of Tevet, three other fast days mourn the Holy Temple's destruction. They are the 17th of Tammuz, the day the Jerusalem city walls were breached, the 9th of Av, when the Temple was burned, and the 3rd of Tishrei, when the Jewish governor of those who were left in the Holy Land, was murdered. Only on the 9th of Av does the fast begin at sunset the evening before the date.
However, all four fasts are days meant for soul-searching and repentance, as well as prayers for the Redemption. Prayers designated for fasts and a special Torah reading are added to the service.
The Israeli Chief Rabbinate ruled that the Tenth of Tevet be considered Holocaust Martyr's Day, the general memorial day, Yom Hakadish Hakllali, for those who perished in the Holocaust but whose yahrzeit is unknown. Relatives may recite the kaddish prayer for them on this day and it is customary for the synagogue service to include the "El Malei Rachamim" prayer, said at funerals, on yahrzeits and on the days when Yizkor is said, in memory of all the victims.
Two other events mourned on the fast occurred in close proximity during the Second Temple period: the death of Ezra the Scribe on the ninth of Tevet, and the translation of the Torah into Greek on the eighth of Tevet. The death of Ezra the Scribe expresses the inability to continue the tradition of the Torah in the framework of the clal (the community as a whole), and the translation of the Torah into Greek expresses the enticement after Greek culture.
To read about the Hasmoneans and the fast, click here.
1) The fast begins at alts hashachar (daybreak) and ends at tzeit hakochavim (halackhic nightfall). Most calendars consider alot hashachar a fixed 72 minutes before sunrise, which is the common custom in the USA. In the Far Rockaway/Five Towns area, for example, this calculation of alos hashachar on December 14th is at approximately 5:59 AM. However, preferably, one should not eat after 5:43AM. Tzeis hakochavim is at approximately 5:14 PM (but see note). In Jerusalem, the fast begins at 4:55 AM according to Heichal Shlomo and at 5:13 according to Beit El Yeshiva and ends at 5:02 PM. Times for other places can be found here.
2) Although the fast does not begin until alot hashachar, once one sleeps a sheinat keva (regular/substantial sleep) on the preceding night (Monday night), the fast is considered to have begun unless one made a t’nai (stipulation) before going to sleep (see note) that one does not wish the fast to begin until morning. Thus, one who wishes to wake up before alot hashachar to eat before the fast begins must make a t’nai before going to sleep on Monday night. (See note).
3) Even if one made a t’nai, one may not begin to eat a bread meal or otherwise significant meal within one half-hour before alot hashachar.
4) All healthy men and women, as well as boys and girls over the age of bar- and bat-mitzvah, are obligated to fast. One may not eat or drink even minute amounts. Nevertheless, if one ate less than a k’zayit or one drank less than m’lo lugmav, one has not broken one’s fast and may still say Aneinu in Sh’moneh Esrei (with the standard text) and receive an aliyah (see below, #11–14). One who ate more than a k’zayit or drank more than m’lo lugmav when not permitted by halakha (see below) is considered to have broken one’s fast, but may still not eat or drink during the rest of the fast.
5) Children under the age of bar- and bat-mitzvah should not fast – even part of the day. However, once children are old enough to understand the concept of a ta’anit tzibbur, their parents should train them – due to the mitzvah of chinuch – to not indulge in the eating of sweets and the like.
6) One who is ill (see note), and pregnant or nursing women who do not feel well, need not fast. A nursing woman who feels fine but is concerned her milk supply will be affected negatively by her fasting should not fast (see note). A postpartum woman who is not nursing need not fast during the first thirty days following childbirth. If she had a cesarean section and still feels weak after 30 days have passed, she need not fast, since she is considered ill.
7) Those over bar- and bar-mitzvah who are not fasting due to health reason may eat and drink regularly, but should not indulge in the eating of sweets and the like.
8) One who must take a pill during the fast should swallow it without water. See note.
9) The special prohibitions of Yom Kippur (bathing, anointing oneself, and wearing shoes) do not apply to Asarah B’Tevet. Nevertheless, it is meritorious to not bathe one’s body in hot water on Asarah B’Tevet (but see note), unless it falls on Erev Shabbat. There is no reason whatsoever to refrain from washing one’s hands, face, and feet with hot water, or from bathing in lukewarm water (even when it falls during the week).
10) One should not brush one’s teeth or rinse out one’s mouth on the fast. If one is inordinately particular and is very disturbed by the foul taste in one’s mouth upon awaking, one may brush or rinse out one’s mouth if one is careful to tilt down one’s head to ensure that one does not swallow any water.
11) In Sh’moneh Esrei of Minchah (see note 15) we insert the prayer of Aneinu in the b’rachah of Shema Koleinu. If one forgot to say it and already said the words Baruch Attah Hashem at the end of the b’rachah, one should not endeavor to correct oneself there. Rather, one should insert Aneinu at the end of Elokai-Netzor, before the Yih’yu L’ratzon that immediately precedes Oseh Shalom at the end of Sh’moneh Esrei.
12) One who is not fasting for whatever reason may not say Aneinu in Sh’moneh Esrei, even if one had been fasting earlier in the day (see note). If one is still fasting, one may say Aneinu in Sh’moneh Esrei, even if one intends to subsequently break one’s fast for whatever reason.
13) One who is not fasting for whatever reason may not receive an aliyah on the fast day –at Shacharit or at Minchah. However, if he is called to receive an aliyah during Shacharit and the fast is on Monday or a Thursday (see note), he should take the aliyah; but if he is called to receive an aliyah during Minchah, or during Shacharit when the fast is on a different day of the week, he should decline the aliyah.
14) The rulings presented in the preceding paragraph also apply to one who is still fasting but intends – for whatever reason – to break his fast before it ends, with one leniency: If he is called to receive an aliyah and he is embarrassed to admit that he plans to break his fast, he need not decline the aliyah (even at Minchah, and even at Shacharit on days other than Monday and Thursday), since he is still fasting at that time.
 See Zecharyah 8:19 and Gemara Rosh Hashanah 18b.
 Shulchan Aruch Orach Chaim 564:1. The Bi’ur Halacha (89:1 s.v. V’im Hispaleil) points out that daybreak is not the time at which the “Morning Star” is visible; that star is visible considerably before daybreak.
 This is the time at which the sun is positioned 16.1 degrees below the eastern horizon. The reason for this calculation is that generally halachic times are not determined by fixed times, but by astronomical calculations.
 This is the time at which the sun is positioned 7.12 degrees below the western horizon.
 One who finds fasting difficult may eat at 5:07 PM. [The explanation for this leniency is beyond the scope of this article.]
 Generally assumed to mean at least one-half hour in bed. See S.A. O.C. 4:15-16; Mishnah Berurah 4:34; and Bi’ur Halacha s.v. David.
 Ohr L’tziyon vol. 3, 31:2 writes that one must make the t’nai verbally. However, in Kara Alai Mo’ed (chapter 1, note 7) Rav Chaim Kanievsky is cited as ruling that although l’chatchilah (initially/preferably) one should make the t’nai verbally, if one merely thought the t’nai it is sufficient b’dieved (ex post facto).
 S.A. O.C. 564:1.
 According to some Poskim (halachic authorities) the same stringency applies to drinking. Others, however, are more lenient (see Rema ad loc.). L’chatchilah one should be sure to make a t’nai to allow drinking as well. B’dieved, if one did not make a t’nai, one may be lenient and drink until alos hashachar if one is accustomed to drink upon awaking (M.B. 564:6).
 Due to the obligation to daven (pray) before one eats. See S.A. 89:3; Rav Chaim Kanievsky (cited in Ishei Yisrael, Appendix, Responsum #86).
 S.A. O.C. 550:1.
 M.B. 567:3.
 An olive size amount of food; approximately the equivalent of 1 fluid ounce.
 A cheek-full; 1–1.3 fluid ounce, depending on the size of one’s cheek.
 Ashkenazic custom is that individuals say Aneinu only during Minchah; only the Chazan says it during Shacharis. Sephardic custom is that even individuals say it during Shacharis and Minchah (see S.A. O.C. 565:3).
 In contradistinction to the halacha presented in note 35.
 M.B. 568:5.
 S.A. O.C. 568:15.
 M.B. 550:5. See also Dirshu Mishnah Berurah (ad loc.), who cites Halichos Shlomo and Orchos Rabeinu that the custom for children to complete the three fasts that immediately precede their bar- and bas-mitzvah has no halachic basis. (It should be noted, however, that Jews of German origin have a strong custom dating back (at least) several hundred years for children to complete the three fasts that immediately precede their bar- and bas-mitzvah.)
 A father is obligated in the chinuch (training) of his young children (under bar- and bas-mitzvah) to perform mitzvos that the children will be obligated to perform when they become older. (Some say a mother is also obligated in chinuch of her children; see M.B. 343:2 and 640:5) In general, the age of chinuch is 6-7, depending on the maturity of the child.
 M.B. ibid.
 Even if one is not unhealthy enough to be considered a choleh (ill person) with regard to permitting refu’ah (healing) on Shabbos, if one feels weaker than the general population while fasting, or if one is weak by nature, one is considered ill with regard to fasting and need not fast (Igros Moshe O.C. 44:114).
 S.A. O.C. 554:6; Rema O.C. 550:1; M.B. 550:3. The Mishnah Berurah (following the earlier Poskim) differentiates between the first trimester of pregnancy and afterwards, and rules that pregnant women may be lenient only after the first trimester has passed, unless they are in great discomfort. Contemporary Poskim note that nowadays pregnant women during the first trimester are often very uncomfortable and nauseated and, therefore, generally need not fast. It follows then that a woman who performed a pregnancy test and discovered she is pregnant but does not feel any discomfort must fast.
 See Dirshu Mishnah Berurah 550:5 n.e. end of note 9. Sephardic women who are nursing may be even more lenient; see Sh”ut Yechaveh Da’as 1:35 and Yalkut Yosef, Kitzur Shulchan Aruch volume 2, 550:10 for the particulars.
 S.A. O.C. 554:6.
 M.B. 550:5.
 The following procedure is effective: One sits and leans one’s head back, and places the pill on the back of the tongue. At the point that one starts to gag, it can be swallowed easily. If one can absolutely not swallow a pill without water, one may swallow a pill with a small amount (less than 1 ounce) of water.
 S.A. O.C. 550:2.
 i550:6. See, however, Sha’ar Hatziyun 550:8 where he writes that the custom was to not bathe in hot water. Nevertheless, in the Mishnah Berurah he rules more leniently that only a ba’al nefesh (that is, a pious person; see Rashi to Gemara Niddah 16b s.v. Ba’al Nefesh) should refrain from bathing in hot water. Rav Shmuel Kaminetzky (Bein Hametzorim 2:3) rules somewhat more strictly that it is good to act strictly and not bathe in hot water. It would seem that this is not the common custom in America.
 Sha’ar Hatziyun 550:8.
 S.A. O.C. 567:3.
 M.B. 567:11.
 S.A. O.C. 565:1.
 S.A. O.C. 565:2; M.B. 565:7. This Yih’yu l’ratzon is sometimes referred to as the “second Yih’yu l’ratzon” to distinguish it from the first Yih’yu l’ratzon, which is proper to say before the beginning of Elokai-Netzor.
 Bi’ur Halacha 565:1 s.v. Bein Yachid. This ruling applies to one who was not required to fast. However, one who was required to fast and mistakenly ate or drank – and is thus required to fast the rest if the day – may say Aneinu. If one ate or drank more than the amount to be considered breaking the fast (a k’zayis of food or a m’lo lugmav of beverage), instead of saying the words b’yom tzom ta’aniseinu (on the day of our fast), one says b’yom tzom hata’anis hazeh (on this fast day) – M.B. 568:3, as explained by Sh”ut Sheivet HaLevi (8:131).
 Rema O.C. 562:1; M.B. 562:7.
 Be called up to “read” from the Torah.
 S.A. O.C. 566:6.
 Such that there would be Torah Reading even had it not been a fast day. Note: Asarah B’Teves actually cannot fall on a Monday; the halacha is presented in Shulchan Aruch (and in this article) as Monday or Thursday since it pertains also to other fast days, some of which can fall on a Monday.
 M.B. 566:19.
 M.B. 566:20.
 Sha’arei Ephraim 1:10.