The Chanukiyah
When Judah the Maccabee decreed an eight day holiday to commemorate the rededication of the Temple and the miracle of the oil, the people began to light the eight lights of the festival. It soon became obvious that it was easier to light a single lamp with eight wicks than eight, separate, clay oil lamps. Thus the Chanukah menorah was born.

The major difference between the Temple Menorah and the Chanukiyah is obviously the number of branches. While the Temple Menorah had seven, the Chanukiyah has eight. Commonly, there is also the addition of a ninth lamp called the shammash (or "helper") which is used to light the lamps each night (since it is forbidden to make use of the Chanukah lights themselves).

Why not a Seven Branched Menorah

But why not use a seven-branched menorah on Chanukah if it symbolizes a miracle associated with the ancient Temple Menorah?

The answers given are based on different sources for the celebration of the festival of Chanukah, and include:

• The lights of the Temple Menorah lasted for eight days after the purification of the Temple (Shabbat, 21b). The festival was declared for eight days and each branch of the chanukiyah represents another day.

• The Maccabees found eight iron pipes in the Temple which they then erected, filled with oil, and kindled (Midrash: Pesikta Rabbah 2:5).

• After the destruction of the Second Temple, a prohibition was placed on making replicas of the seven branched Temple Menorah (see Rosh Hashanah 24a, Avoda Zara 43a). The lighting of eight lights thus enabled the dedication of the Menorah to be celebrated without transgressing this prohibition (after R. Abraham Isaac Kook, first Chief Rabbi of Israel, 1921-35).