The term ‘Rosh Chodesh’ literally means ‘head of the month’, but translates to ‘New Month’ in English. It is the day(s) on which a new month begins and is considered to be a minor festival in Jewish tradition. As the Jewish calendar has lunar months, all months are either 29 or 30 days long.
In Exodus 12:2 we are told “This month [Nissan] shall mark for you the beginning of the months; it shall be the first of the months of the year for you.” This is the first commandment given to the Jewish nation communally: to have a calendar starting with the month of Nissan.
THE JEWISH CALENDAR IS A LUNAR ONE
Fasts, festivals, holidays and special occasions are regulated by the cycles of the moon.
Before the era of the fixed calendar, Jews used to determine the beginning of a new month using eyewitnesses. At the end of a 29-day period, witnesses would observe the moon in order to see if it had reappeared or not. These witnesses would then tell the judges of the religious court (Sanhedrin) what they had seen, and the rabbis would decide whether or not the observations were satisfactory. (If they were not satisfied, then that day was added to the number of the expiring month and the next day became the start of the new month. In a case such as this one, the 30th day of the previous month as well as the first day of the next month would be Rosh Chodesh.)
The Jews would then be told, and the new month would be signalled by torches being lit on hilltops. Jews in other communities would see the torches and in turn would light their torches and so on, thus spreading news of the new month quickly until everyone knew it was Rosh Chodesh.
These days, the Sanhedrin no longer exists and the date of the new moon is no longer determined by observation but instead by calculation. When the moon is exactly between the earth and the sun, the new month begins (called molad in Hebrew, meaning ‘birth’).
HOW DO WE CELEBRATE ROSH CHODESH?
In the Bible, Rosh Chodesh is considered a particularly important time, equivalent to Shabbat and Yom Tov. People in Biblical times may not have even worked on this (these) day(s).
Rosh Chodesh is often linked to women, because of the Biblical women’s refusal to relinquish their jewellery to the men who were building the Golden Calf, according to midrash Pirke DeRabbi Eliezer (chapter 45). As a reward, God gave the women an extra holy day each month, free from work. It is customary to wear new clothing on Rosh Chodesh, in celebration of the day’s special character. In observant societies there are restrictions on the work women may undertake on Rosh Chodesh, such as a ban on spinning, weaving, and sewing — the skills which women so enthusiastically contributed to the building of the Mishkan (Tabernacle). For many women in Jewish communities today, Rosh Chodesh is a time to come together, to study Torah and observe the different seasons. Most major cities have Rosh Chodesh groups. Some are only for women and some are open to all.
PRAYERS & SYNAGOGUE SERVICES FOR ROSH CHODESH
In synagogue, the impending arrival of the new month is announced on Shabbat Mevarchim, the Shabbat (Sabbath) before the new month, and Birkat haChodesh (the blessing for the new month) is said after the Torah reading.
Hallel, psalms praising God, are said on Rosh Chodesh, the Torah is read (even if it is not Shabbat, Monday or Thursday, the days on which the Torah is normally read), and Musaf (the Additional Service) is said.
During the Amidah and Birkat haMazon (Grace After Meals), we add the paragraph beginning Ya’aleh V’yavo.
In ancient times extra offerings were made in the Temple on Rosh Chodesh, especially a sin offering for unwitting transgressions. Today, we pray the Musaf (Additional Service) as a substitute.
Aish HaTorah: Rosh Chodesh
My Jewish Learning: Rosh Chodesh 101
Judaism 101: Rosh Chodesh
Jewish Virtual Library: Jewish Holidays: Rosh Chodesh
Wikipedia: Rosh Chodesh
Hillel.org: Understanding Rosh Chodesh