First printing of the Zohar, the fundamental work of the Kabbalah (Jewish esoteric and mystical teachings), authored by the Talmudic sage, Rabbi Shimon Bar Yochai.
Links: The Kabbalah
Av 20 is the anniversary of the passing of the Lubavitcher Rebbe's father, Rabbi Levi Yitzchak Schneerson (1878-1944), in Alma Ata (currently Almaty), Kazakhstan. Rabbi Levi Yitzchak was Chief Rabbi of Yekaterinoslav (currently Dnipro), Ukraine, and was arrested and exiled to Kazakhstan by the Stalinist regime as a result of his work to preserve Jewish life in the Soviet Union.
Links:
A Brief Biography
Rebbetzin Chana Scneerson's biography, which includes her account of her husband's heroism, arrest and passing.
There are those who chase all things of heaven—and find they cannot live.
There are those who chase all things of earth. Their life is not worth living.
Heaven desires the earth, and the earth is lost without heaven. Make your life a marriage of the two, as lovers that never part, and you will find peace.