But it's not. Today until sunset is the last day of Chanukah. To put an exclamation point on that observation, the rabbis assigned a Torah reading for this morning that includes a verse from the book of Numbers that seems to shout out, "Zot Chanukah!" "This is Chanukah!" (Literally, the verse says, "This is the dedication of the altar on the day of its anointing," but the word for dedication in Hebrew is "chanukah." Numbers 7:84.)
You could ask why the last day of Chanukah, the eighth day, is the day that is known as Zot Chanukah. Aren't the first seven days also Chanukah? One answer is that the eighth and final day of Chanukah is the day whose meaning encompasses and transcends the meaning of all of the other days of the festival.
In Jewish tradition, the number seven is often associated with completeness and wholeness. There are seven days of creation and seven branches of the Temple Menorah. Shabbat is the seventh day that completes the week. However, the number eight (seven plus one) also appears in some interesting places. The covenant of circumcision takes place on the eighth day of life. The Torah was given on Shavuot, the day after we complete the counting of seven weeks. The seven days of Sukkot are not complete until we celebrate Shmini Atzeret, which the Torah literally calls the eighth day of the seven-day holiday (Leviticus 23:36 and Numbers 29:35).
Eight signifies completion beyond the ordinary. The eighth day is the time when something extraordinary happens. It is the day that we declare that we have stepped beyond the normal counting of time (a week) and into the realm of time beyond time. That is why the Torah is given on day "seven plus one," to signify that it exists outside of time. It is why we circumcise a baby boy on a day beyond time to declare, paradoxically, that he is not really "whole" until he has had a piece of him removed to enter into the covenant.
Today, the eighth day of Chanukah, is called Zot Chanukah, "This is Chanukah," because it is the culminating moment of the miracle that contains the entirety. Even after all the oil is spent and the final candles have guttered, we feel the building of the light within us even more strongly. We rededicate ourselves at the darkest time of the year, to increase the light within us and throughout the world.