"There are rituals of the elements and feasts of the times. A feast for the first night of the Prophet and his Bride! A feast for the three days of the writing of The Book of the Law. A feast for Tahuti and the child of the Prophet-secret, O Prophet! A feast for the Supreme Ritual, and a feast for the Equinox of the Gods. A feast for fire and a feast for water; a feast for life and a greater feast for death! A feast every day in your hearts in the joy of my rapture! A feast every night unto Nu, and the pleasure of uttermost delight! Aye! feast! rejoice! there is no dread hereafter. There is the dissolution, and eternal ecstasy in the kisses of Nu." (AL II:36-44)
The rituals of the elements and feasts of the times are celebrated at the equinoxes and solstices. Some Thelemites go one step farther and divide the year into cross-quarters as well, creating eight holidays not dissimilar to the "wheel of the year" often seen in other Neo-pagan traditions. While the equinoxes and solstices naturally fall on the same day as they do for other Neo-pagan traditions, the cross-quarter holidays are all shifted slightly, for example, Samhain (ritual of water) falls at 15 degrees Scorpio which is closer to November 7th than October 31st.
The Feast for the First Night of the Prophet and his Bride is celebrated on August 12th. There is no formal celebration that I am aware of. One O.T.O. body with which I am affiliated has an ice cream social on that date.
The Feast for the Three Days of the Writing of The Book of the Law is celebrated on April 8, 9 and 10, the three days that Crowley wrote Liber AL. Each day, beginning at noon, celebrants read aloud one of the three chapters of the Book of the Law.
The Feast for the Supreme ritual is the Thelemic New Year. This holiday, falling on March 20th, commemorates an invocation of Horus.
The Feast for the Equinox of the Gods is celebrated at the Spring Equinox to honor the founding of Thelema in 1904.
The Feast for Life (also called the lesser feast) is a celebration of a new birth. A person's birthday is sometimes referred to as the "lesser feast" as well. The Feast for Fire is the celebration of a boy's reaching puberty and the Feast for Water is the celebration of a girl's reaching puberty. The Greater Feast for Death (often just called the greater feast) is the commemoration of an individual's death.
Some Thelemites also celebrate "Crowleymas" which is the anniversary of Crowley's birth (October 12th).
Books You Might Enjoy:
Aleister Crowley - The Hermit Hymn To Solitude
Morwyn - The Golden Dawn
Thomas Moore - Candle Magick For Love
Anonymous - Pagan Holidays
Frater Hoor - A Thelemic Calendar