Rosh Hashanah, the Jewish New Year and start of the 10 holiest days in the Jewish calendar, began yesterday evening at sundown. Rosh Hashanah starts with the birth of a new moon. The black night symbolizes the dark days of repentance that follow and a new beginning that comes with forgiveness from God and others for past transgressions.

The term "High Holy Days" usually refers to Rosh Hashanah, Yom Kippur and the seven days between. But some Jews don't consider the holidays complete until Simhat Torah, a celebration that follows the week-long festival of Sukkot.

The Jewish calendar is determined by a formula that uses both lunar and solar elements. As a result, holiday dates vary from year to year but fall during the same season. The following are this year's dates:

* Rosh Hashanah, Sept. 10 and 11. The Jewish New Year is a celebration of the birth of creation and the beginning of a period of personal and communal introspection.

Reform Jews observe only one day of Rosh Hashanah. Conservative and Orthodox Jews attend synagogue on both days, with long services exceeded only by those on Yom Kippur. A shofar, or ram's horn, is blown at frequent intervals, calling the people to spiritual awakening as proclaimed in Numbers 29:1. Some congregations do not blow the shofar if one of the two days is Saturday, the Sabbath, as occurs this year.

Rosh Hashanah also is called the Day of Judgment because it begins a 10-day period known as the Days of Awe or Days of Repentance. It is a time to reflect on misdeeds of the past year against God and others and to ask forgiveness from each of them, to improve one's standing in God's Book of Life.

The new year also is a time of remembrance, including visiting the graves of those who have died, and sending cards to friends and relatives. Some spend increased time in Bible study and prayer. Others complete unfinished tasks and make resolutions for improving their lives.

* Yom Kippur, Sept. 20. The goal of soul-searching and repentance is reconciliation, and this Day of Atonement marks that achievement for those who fulfill their religious obligations.

The eve and day of Yom Kippur are spent in worship, fasting, prayer and meditation. The evening service begins with the chanting of Kol Nidrei, a request for forgiveness for any vows and promises that may be made, but not kept, in the coming year. Friends ask for and express forgiveness for past offenses.

Services resume the next morning and continue all day. They include readings from the Torah and penitential prayers and conclude at dark with the blowing of the shofar. Some congregations invite all trained shofar blowers to participate in this final sounding of the horn.

* Sukkot, Sept. 25-Oct. 2. Called the Feast of Tabernacles, or the Feast of Booths, Sukkot commemorates the wandering of the Israelites in the desert after the exodus from Egypt. Participants build temporary huts with wood or canvas walls and roofs and spend as much time as possible in them, including eating, lighting candles and praying. The seventh day is a joyous celebration called Hoshana Rabba, the Great Hosanna, which seals God's judgment that began on Rosh Hashanah.

* Simhat Torah, Oct. 3. Rejoicing of the Law marks the completion and new beginning of the annual cycle of reading the Torah in the synagogue. Every member receives a blessing, and Torah scrolls are taken from the carefully decorated ark where they are kept on the bimah, or platform, and carried through the synagogue. Children follow the procession, waving flags, or join other members in unrolling and rerolling the Torah scrolls and dancing in celebration.