The Fast of Tevet [עשרה בטבת] falls on the tenth day of the month of Tevet. Asara B'Tevet is a minor fast day. A fast is observed from sunrise to sunset in memory of the the beginning of the siege of Jerusalem by Nebuchadnezzar (588 BCE, 2 Kgs. 25:1-4) which ultimately resulted in the breaching of the walls of the city (17^th Tammuz 586, Jer. 52:6-7), the destruction of the Temple of Solomon three weeks later (9^th Av) and the conquest of Judah and the consequent exile.
Asara B'Tevet is therefore a part of the series of Fast Days which are connected with the destruction of Solomon's Temple:

1. The beginning of the Siege, Asara B'Tevet, 10^th Tevet
2. The breaching of the City walls, 17^th Tammuz
3. The destruction of the Temple, Tisha B'Av (9^th Av)
4. The Fast of Gedaliah (Tzom Gedaliah, 3 Tishri)
   

The Chief Rabbinate in Israel has, in modern times, also been marked Asara B'Tevet as a day of remembrance [a general kaddish day] for all those who died in The Shoah [The Holocaust] especially those who lack a definite date of death and so have no identifiable yahrtzeitץ

[עשרה בטבת, Yiddish, anniversary, lit. "time of [one] year.]

The Hebrew word erev means evening. The Jewish day begins in the evening. Erev Shabbat is Friday evening.

The Book of Genesis (1:14) speaks of the “lights in the dome of the sky” that set the days apart as signs of “set times/seasons” for the days and years. The Hebrew word for “set times” is moadim/festivals. Jewish festivals are events in time that are “sacred markers”; witnesses to the sacred. The Jewish festivals are: Shabbat (Sabbath), Rosh Hashanah, Yom Kippur, Sukkot (Tabernacles), Shemini Atzeret, Simchat Torah, Chanukah, Purim, Pesach (Passover), and Shavuot (Pentecost)

According to the Torah the days between Passover and Shavuot are to be counted (Lev. 23:15-16; Deut. 16:15-16). These 49 days of counting, which relate to the offering of an omer of barley, (called in Hebrew Sefirat Ha'Omer) are likened to a connecting thread between the Passover from Mitzrayim [Egypt] and the Giving of the Torah at Sinai.

Lag Ba'Omer (falling on 18^th Iyyar) is the 33^rd day of counting which, according to tradition recorded in the Kitzur Shulchan Aruch (120:1-10), signals a small break in the counting to celebrate the ending of the "great plague," a perceived "divine sent" plague during the Counting of the Omer [Sefirat Ha'Omer] in Rabbi Akiva’s time (2^nd Century). The Talmud relates (Yevamoth 62b) that 2400 of Rabbi Akiva's disciples died at the same time because they did not treat each other with respect and the "world" remained desolate of learning until R. Akiva taught new masters. These new masters [R. Meir, R. Judah, R. Jose, R. Simeon, and R. Eleazar b. Shammua] revived the Torah.

Another tradition suggests that the R. Akiva's students died at the hands of the Romans during the Bar Kochba revolt. The celebration of Lag Ba'Omer with a break in fasting and the lighting of bonfires is, perhaps, a reflection of this tradition.

Yet another traditional celebration by some Jews at Lag Ba'Omer is the memorial of the death of R. Shimon. It is a kabbalistic belief that through one of R. Akiva's five students who survived the plague, R. Shimon [R. Shimon bar Yochai; Rashbi; aka. R. Simeon,] Israel received the mystical Torah, The Zohar. This hidden and mystical Torah transmitted through R. Shimon is a complement to the revealed Torah given through Moses.

The word "lag" is a shorthand way for writing 33, a number which is written in Hebrew as lamed gimel [לייג]. Lag Ba'Omer is thus the 33rd day of the counting of the omer. An omer is a measure of barley. The counting of the days in the omer [ba omer = meaning, in the omer—Shephardic Jews call the days la omer meaning, of the omer] is a practice which dates from biblical times (Lev. 23:15-16) when, from the second day of Passover through to Shavuot [seven weeks,] a sheaf of barley the size of an omer was brought to the Temple in Jerusalem. After Shavuot the offering changed from barley to wheat. It is because Shavuot marks the end of the 49 days of counting of the omer that Shavuot is also referred to as the Feast or Festival of Weeks. Shavuot, being the 50th day after Passover was named Pentecost by Hellenic Jews. See below for Sefirat Ha'Omer, The Counting of the Omer.

Passover (Pesach) is the Jewish festival that remembers and relives the experience of God’s saving intervention in the history of Israel. The original Passover events are celebrated and retold every year during the Passover Seder, as though “each and every Jew living today were themselves part of the experience” (Maimonides, Mishneh Torah).

Purim celebrates the miracle of the deliverance from persecution and suffering wrought for the Jewish people in Persia. The story is told in the Book of Esther (Megillat Esther) c. 4^th Cent. BCE.

In cities that were surrounded by a wall in the time of Joshua Purim is celebrated on the 15^th day of Adar, also called Shushan Purim.

The story of Purim which is recounted in the Hebrew Bible, in the Megillat Esther, dates from the 4^th Century BCE and is the last of the canonical texts to be determined for inclusion in the Tanakh. The Talmud attributes Megillat Esther to a redaction of an original text written by Mordechai (Baba Bathra 15a). The Book of Esther in the Septuagint [Greek Bible] differs from Megillat Esther and is understood as an interpretive adaptation. The Greek Esther (c. 2^nd Century BCE) adds additional traditions, e.g., Ahasuerus is identified with Artaxerxes.

Jerome's Latin text [Vulgate] of the Book of Esther is a translation of the Hebrew text with additions based upon the Greek version. Read more...

In a leap year, there are two months of Adar (Adar I & Adar II) and the celebration of Purim is moved to Adar II. However, Purim, together with Shushan Purim is celebrated in a minor way in Adar I. This celebration is called Purim Katan [and Shushan Purim Katan.] The word katan means “little” or “small.”

There is a strong connection between Purim Katan and Purim since it is the only observance (together with Shushan Purim Katan) which remains to be celebrated twice, in both months of Adar, in a leap year. The Talmud states, that

“There is no difference between the fourteenth of the first Adar [Purim Katan] and the fourteenth of the second Adar [Purim Sheni] save in the matter of the reading of the Megillah and gifts to the poor”

(BT. Megillah 6b).

Although it is a “little” Purim without the set observances of Purim, Jewish practice is to avoid mourning and fasting on Purim Katan, to omit the Tachanun (supplication prayers) after the Amidah prayer during Shacharit (morning) and Minchah (afternoon) services, and to celebrate the holiday with joy.

Rosh Hashanah, New Years Day, the first day of the Days of Awe, Yamim Noraim, is one of the holiest days in the Jewish year. Synagogue services focus on God’s sovereignty. It is customary to each apples dipped in honey on Rosh Hashanah and to wish everyone “Happy New Year, and sweet one.”

Shabbat (Sabbath), a recurring weekly festival; a day of rest in honor of Creation and Redemption, beginning at sundown on Friday evening and “going out” at sundown Saturday.

Shavuot is one of the three pilgrimage feasts. Shavuot, also called Hag Hashavuot/The Festival of Weeks, has agricultural roots in the “first fruits” of the harvest, and spiritual links to the giving of the Torah on Mount Sinai. Shavuot is often called Hag Matan Torateinu (The Festival of the Giving of Our Torah.) Read more...

At the conclusion of the festival of Sukkot there are two holidays, Shemini Atzeret and Simhat Torah. In Israel, and for Liberal Jews, these are celebrated on the same day. For other Jews throughout the diaspora (where holidays are observed over two days) Simchat Torah is celebrated on the second day of Shemini Atzeret.

Shemini Atzeret, the “assembly of the eighth day,” is celebrated at the end of Sukkot (after the seventh day.) A Rabbinic midrash says that God desired one more day of intimacy with Israel and said to them, “Your departure is difficult for me. Stay with me one more day.” Shemini Atzeret is not a part of Sukkot but a separate holiday in it's own right.

On Shemini Atzeret the prayer for rain, teffilat geshem, is inserted in the second blessing of the Amidah prayer, replacing the prayer for dew recited since the beginning of Passover.

The Book of Leviticus teaches “You shall dwell in booths for seven days” (23:42). The Sukkot festival is related agriculturally to harvest, historically to forty years of “wandering” in the wilderness, and spiritually to rejoicing in the gifts and bounty that God has brought and wrought. Sukkot is called the Season of our Joy. It is customary to make a lulav for waving at prayer time during Sukkot.

The Fast of the First Born which commemorates the saving of the first born of Israel is observed by first born Jewish males on the day preceding Passover.

Tisha B’Av, the Ninth Day of Av, is a fast day of mourning for the many tragedies of Jewish history. Read more...

Tu B’Shvat is New Year for Trees, the 15^th of the month of Shvat. This is the time for calculating the age of trees for tithing.

Tzom Tammuz is a fast day remembering the breaching of the walls of Jerusalem, culminating in the destruction of the 1st Temple.

Yom Kippur, The Day of Atonement, is the holiest and most solemn day on the Jewish calendar. Yom Kippur falls on the 10^th day of Tishri, at the culmination of forty days of repentance. These days of repentance include: the month of Elul (30 days), followed by Rosh Hashanah (the 1^st day of Tishri)—the beginning of Ten Days of Awe. Yom Kippur is the final Day of Awe, 10^th Tishrei.