Aaron the first High Priest, brother of Moses and Miriam, passed away at age 123 on the 1st of Av of the year 2487 from creation (1274 BCE). This is the only yahrzeit (date of passing) explicitly mentioned in the Torah (Numbers 33:38).
Links:
A Midrashic description
of Aaron's passing
More about Aaron
"Aaron" and "On the Essence of Circumstance" -- a spiritual profile based on the Lubavitcher Rebbe's talks
Following their long journey from Babylon (see Jewish history for the 12th of Nissan), Ezra and his entourage arrived in the land of Israel to be near the newly built second Holy Temple in Jerusalem. A relatively small group came together with Ezra, the majority of Jews, including great Torah scholars, choosing to remain in Babylon due to the harsh conditions that were then prevailing in Israel.
Link: Ezra the Scribe
Today is Rosh Chodesh--"Head of the Month"--for the Hebrew month of "Av" (also called "Menachem Av").
Special portions are added to the daily prayers: Hallel (Psalms 113-118) is recited -- in its "partial" form -- following the Shacharit morning prayer, and the Yaaleh V'yavo prayer is added to the Amidah and to Grace After Meals; the additional Musaf prayer is said (when Rosh Chodesh is Shabbat, special additions are made to the Shabbat Musaf). Tachnun (confession of sins) and similar prayers are omitted.
Many have the custom to mark Rosh Chodesh with a festive meal and reduced work activity. The latter custom is prevalent amongst women, who have a special affinity with Rosh Chodesh -- the month being the feminine aspect of the Jewish Calendar.
Links: The 29th Day; The Lunar Files
"When Av begins, we diminish [our] rejoicing" (Talmud, Taanit 26b).
On the 1st of Av, "The Three Weeks" mourning period over the destruction of the Holy Temple--which began 13 days earlier on Tammuz 17--enters an intensified stage. During "The Nine Days" from Av 1st to the Ninth of Av, a heightened degree of mourning is observed, including abstention from meat and wine, music, bathing for pleasure, and other joyous and enjoyable activities. (The particular mourning customs vary from community to community, so consult a competent Halachic authority for details).
Consumption of meat and wine is permitted on Shabbat, or at a Seudat Mitzvah (obligatory festive meal celebrating the fulfillment of a mitzvah) such as a Bris (circumcision), or a "Siyum" celebrating the completion of a course of Torah study (i.e., a complete Talmudic tractate). The Lubavitcher Rebbe initiated the custom of conducting or participating in a Siyum on each of the Nine Days (even if one does not avail oneself of the dispensation to eat meat).
Citing the verse (Isaiah 1:27) "Zion shall be redeemed with mishpat [Torah] and its returnees with Tzedakah," the Rebbe urged that we increase in Torah study (particularly the study of the laws of the Holy Temple) and charity during this period.
There are three ways to bring unity between two opposites:
One
Introduce a power that transcends them both, and to which they both utterly surrender their entire being.
Externally, they now seem at peace with one other, because they are both under the influence of the same force.
But they themselves know that they are not truly at peace, and that such peace cannot endure, because their own being is simply ignored.
Two
Find a middle ground where the two meet.
The two are now at peace, but only on that middle ground
The rest of their territory remains apart, distant, without room for the other.
Three
Reach deeper, into the very essence of the two beings, and discover that at this point, in every aspect, they are no more than two expressions of the same one G-d.