Tonight and tomorrow we will celebrate, besides Ḥanuka, Rosh Ḥodesh Tebet.
In the Tanakh (Hebrew Bible) the name of this month is Ḥodesh ha'asiri, the tenth month. In the Tora the months are named numerically (first, second, etc) counting from Nisan. The name Tebet was coined in Babylonia, same as the other commonly used names of the Hebrew months (Nisan, Iyar, Ḥeshvan, etc.).
Some years, like this year, Rosh Ḥodesh Tebet is observed for one day and some years --last year, for example--for two days. Why? Because Kislev, the preceding month, consists sometimes of 30 days (ma-le) and some years of only 29 days (chaser). The 30th day of the preceding month is always the first day of Rosh Ḥodesh of the next month, and the second day of Rosh Ḥodesh is the 1st day of the new month. This year Kislev has only 29 days, so tomorrow, we will celebrate Rosh Ḥodesh Tebet for one day only.
The month of Tebet itself, is always 29 days long. And because of this lack of variation in its length, Rosh Ḥodesh Shebat, the month which follows Tebet, will always be celebrated for just one day (the 1st of Shebat).
Tonight and tomorrow we will say Ya'ale veYabo and 'al haNisim in the Amida and Birkat haMazon.
In the morning we read the full Halel, then we take out two Sifre Tora. On the first one we read the Rosh Ḥodesh portion, but instead of dividing it into four Aliot, as we do every Rosh Ḥodesh, we divide this text into three Aliot. In the second Sefer Tora we read the text corresponding to the 6th day of Ḥanuka. We also say Musaf of Rosh Ḥodesh, including 'al haNisim.
Do you have any idea how hard it was to find a Jewish zebra?