Thelema does not typically have holidays as most religions. Some Thelemic groups may honor the quarter days of the year as well as any other days they see fit. However, within the book of the law there are several feasts listed and they are found in (II:37-44).
II:37. A feast for the first night of the Prophet and his Bride!
• (August 12) On this day in 1903 e.v., aleister crowley was married to his first wife, Rose Kelly. Rose was to play an important part in the inauguration of the New Aeon and the reception of The Book of the Law.
II:38. A feast for the three days of the writing of the Book of the Law.
• (April 8, 9, 10) Over these three days in April 1904 e.v., aleister crowley received the three chapters of The Book of the Law. These holidays are typically celebrated with readings of each chapter on its respective day.
II:39. A feast for Tahuti and the child of the Prophet--secret, O Prophet!
II:40. A feast for the Supreme Ritual, and a feast for the Equinox of the Gods.
• (March 20) The anniversary of the beginning of the Aeon of Horus in 1904 e.v.. This date also marks the beginning of the Thelemic New Year.
II:41. A feast for fire and a feast for water; a feast for life and a greater feast for death!
• The Equinoxes and the Solstices. The seasonal turning points of the year, traditionally celebrated by many cultures throughout history, are also ritually observed by Thelemites and other practitioners of Magick.
II:42. A feast every day in your hearts in the joy of my rapture!
II:43. A feast every night unto Nu, and the pleasure of uttermost delight!
• The above two passages regarding these feasts are self explanatory
*Other days of honor and celebration
"Crowleymas" (October 12)
The anniversary of Aleister Crowley's birth in 1875 e.v..
Crowley's "Greater Feast" (December 1)
A celebration to commemorate the death of aleister crowley on this day in 1947 e.v..
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Frater Hoor - A Thelemic Calendar