Rosh Chodesh which literally means "Head of the Month" is a monthly holiday that celebrates the arrival of the new moon, marking the start of a new month in the Jewish calendar.
The Jewish Calendar is a lunar calendar with twelve lunar months and 354 days per year. Each lunar month consists of 29 1/2 days. Since it is impossible to switch months in the middle of the day, certain Hebrew months have twenty-nine days whilst others have thirty days.
In order for the Jewish Festivals to be synchronized with the proper season, for example Passover (Pesach) which must fall in the spring (in Israel - the Northern Hemisphere), a leap year is added every few years. In a nineteen year cycle there will be seven leap years.
The Jewish leap year, however, is not like the leap year in the Gregorian calendar which is one day added on at the end of February every four years. A Jewish leap year adds on an entire month to close the gap between the 354 day lunar calendar and the 365 day solar calendar. Since the month of Adar (approximately February-March) is the last month of the Hebrew year, we add on an extra month at this time. We then have Adar I and Adar II which assures us that the holidays will be celebrated in the proper season. Originally, the date of Rosh Chodesh was confirmed on the testimony of witnesses observing the new moon, a procedure known as Kiddush Hachodesh (sanctification of the month). After the Sanhedrin (an assembly of either 23 or 71 elders or rabbi's, appointed to sit as a tribunal in every city in ancient Israel) declared Rosh Chodesh for either a full 30 day month or a 29 day month, news of it would then be communicated throughout Israel and the diaspora.
This system was dependent on the functioning of the Sanhedrin to declare the month, and to communicate this month to far-flung Jewish communities. In the 4th century CE, this became impossible and instead a fixed calendar of 29 and 30 day months was instituted by Hillel.
At the end of a 29 day month, Rosh Chodesh is celebrated for one day, on the first day of the new month. At the end of a 30 day month, Rosh Chodesh is celebrated for two days - the 30th day of the previous month, and the 1st day of the new month.
With the exception of the month of Heshvan, the eighth month of the year, every single month of the Jewish Calendar has some sort of special day or special observance. The importance of Rosh Chodesh is therefore obvious.
The names of the months are not Hebrew but Babylonian. The Bible refers to the Jewish holidays only by the order of the months and not by the Babylonian names which were assigned long after the canonization of the Torah. For example, the Torah gives the date of Yom Kippur as the tenth day of the seventh month, whilst the date of Pesach is the fifteenth day of the first month.
The Hebrew month of Av (אָב) is the fifth month of the Jewish calendar when counting from Nissan, and the eleventh month when counting from Tishrei. It always contains 30 days and is one of the most significant and emotionally powerful months of the Jewish year. The first part of Av is marked by national mourning over the destruction of the First and Second Holy Temples in Jerusalem, while the latter part of the month turns towards comfort, rebuilding, and hope for the future redemption.
The most solemn day of the month is Tishah B'Av (the Ninth of Av), a full 25-hour fast commemorating the destruction of both the First Beis HaMikdash by the Babylonians in 586 BCE and the Second Beis HaMikdash by the Romans in 70 CE. According to our Sages, many other national tragedies also occurred on this day, making it the saddest day of the Jewish calendar. The three weeks of mourning that begin on the 17th of Tammuz reach their climax on Tishah B'Av, during which Jews refrain from eating, drinking, bathing for pleasure, wearing leather shoes, and marital relations, while reading *Megillas Eichah* (Lamentations) and reciting *Kinnos* (lamentations).
The mourning of Tishah B'Av gradually gives way to consolation. The Shabbos immediately following Tishah B'Av is called Shabbos Nachamu, named after the opening words of the Haftorah, Nachamu, Nachamu Ami" ("Comfort, comfort My people" – Isaiah 40:1). This begins the Seven Weeks of Consolation, during which the Haftoros focus on Hashem's promise to comfort Israel and bring the ultimate redemption.
Another joyous day in Av is Tu B'Av (the Fifteenth of Av), regarded by the Mishnah as one of the happiest days of the Jewish year. Historically, it commemorates several joyous events, including the lifting of restrictions preventing marriage between the tribes, the end of the deaths of the wilderness generation, and the removal of roadblocks preventing pilgrimage to Jerusalem. In later generations it became associated with Jewish courtship and marriage, symbolising unity, love, and new beginnings.
According to Sefer Yetzirah, the mazal (zodiac sign) of Av is Aryeh (Leo – the Lion). Although the lion symbolises strength, courage, and royalty, our Sages note that the Beis HaMikdash was destroyed under the sign of the lion, yet the future redemption will also come through the "Lion of Judah," reminding us that even within destruction lies the seed of redemption.
The tribe associated with Av is Shimon (Simeon). Chazal explain that Shimon possessed qualities of passionate intensity and strength, characteristics that, when channelled properly, become powerful forces for serving Hashem.
The precious stone corresponding to the tribe of Shimon on the Choshen Mishpat (High Priest's Breastplate) is traditionally identified by many Orthodox commentators as Pitdah (Topaz), although the precise identification of several of the Choshen's stones has been debated for centuries.
The **Hebrew letter of Av is Tet (ט). The numerical value of Tet is nine, corresponding to the Ninth of Av. Although Tishah B'Av is a day of mourning, the letter Tet also begins the word "Tov" (good), teaching that hidden goodness ultimately emerges even from suffering. This reflects the Jewish belief that the redemption and the rebuilding of the Beis HaMikdash will arise from the very day on which it was destroyed.
According to Sefer Yetzirah, the limb of the month is the left kidney. Chazal describe the kidneys figuratively as organs associated with counsel and inner reflection. During Av, Jews are encouraged to examine their actions, strengthen their relationship with Hashem, and prepare spiritually for the months leading to the High Holy Days.
A well-known teaching of the Sages states: "Mi'shenichnas Av mema'atin b'simchah"—"When Av begins, we reduce our joy" (Taanis 26b), reflecting the mourning observed before Tishah B'Av. However, after the fast the emphasis shifts toward hope and rebuilding, reminding us that Jewish history never ends in despair. The month of Av beautifully captures the Jewish ability to transform tragedy into faith, mourning into comfort, and destruction into the promise of ultimate redemption with the coming of Mashiach.