On the 27th of Cheshvan of the year 1657 from creation (2104 BCE) "the earth dried" (Genesis 8:14) completing the 365-day duration of the great flood that wiped out all life on earth save for the eight human beings and and the animals (at least two of each species) in Noah's ark; on this day G-d commanded Noah to "Come out of the ark" and repopulate, settle and civilize the earth.
[See entry for Cheshvan 17 for a Chronology of the Flood.]
Links: Life in a Box; Lunar Flood, Solar Year; The Discovery of Planet Earth; Noach Parshah Page
This Shabbat is Shabbat Mevarchim ("the Shabbat that blesses" the new month): a special prayer is recited blessing the Rosh Chodesh ("Head of the Month") of the upcoming month of Kislev, which falls on Tuesday of next week.
Prior to the blessing, we announce the precise time of the molad, the "birth" of the new moon. See molad times.
It is a Chabad custom to recite the entire book of Psalms before morning prayers, and to conduct farbrengens (chassidic gatherings) in the course of the Shabbat.
Links: Shabbat Mevarchim; Tehillim (the Book of Psalms); The Farbrengen