When to Celebrate Biblical Holidays
Every Week: Shabbat
Every Month: Rosh Chodesh
Every Year: Three different Shalosh Regalim
Every Spring:
Pentecost (aka Shavuot and Feast of Weeks)
Every Fall:
Yom Teruah (aka Rosh Hashana and Jewish New Year)
Every Winter: Hanukkah
Late Winter/Early Spring: Purim
Every Seven Years:
The Sabbatical Year (aka Shemitah)
Every Fifty Years: Jubilee Year