Sirius [from Greek seirios scorching] In classical myth, the dog of Orion, who followed his master when he was made a constellation; it is called the Dog-star; by the Egyptians, Sothis. The dog at times symbolizes Mercury or Budha, who was called Cynocephalus, the dog-headed. It is a symbol of watchfulness and guarding. The heliacal rising of Sirius coincides in the northern hemisphere with the sultry heat of late summer, and was regarded in antiquity as a cause of that heat, or as contributing a baleful quality to it.

“The star worshipped in Egypt and reverenced by the Occultists; by the former because its heliacal rising with the Sun was a sign of the beneficent inundation of the Nile, and by the latter because it is mysteriously associated with Thoth-Hermes, god of wisdom, and Mercury, in another form. Thus Sothis-Sirius had, and still has, a mystic and direct influence over the whole living heaven, and is connected with almost every god and goddess. It was ‘Isis in the heaven’ and called Isis-Sothis, for Isis was ‘in the constellation of the dog,’ as is declared on her monuments. ‘The soul of Osiris was believed to reside in a personage who walks with great steps in front of sothis, sceptre in hand and a whip upon his shoulder.’ Sirius is also Anubis, and is directly connected with the ring “Pass me not’; it is, moreover, identical with Mithra, the Persian Mystery god, and with Horus and even Hathor, called sometimes the goddess Sothis. Being connected with the Pyramid, Sirius was, therefore, connected with the initiations which took place in it. A temple to Sirius-Sothis once existed within the great temple of Denderah. To sum up, all religions are not, as Dufeu, the French Egyptologist, sought to prove, derived from Sirius, the god-star, but Sirius-Sothis is certainly found in connection with every religion of antiquity” (TG 300).

http://www.the-equinox.org/vol1/no2/eqi02020h.html

(Equinox vol.1 part II – from RITUAL OF THE 4° = 7^¤ GRADE OF PHILOSOPHUS under The Pyramid of the Four Elements – a book by Crowley)

This Key represents a Star with seven principal and fourteen secondary rays, altogether twenty-one, the number of the divine name Eheieh. In the Egyptian sense it is Sirius, the Dog-Star, the star of Isis-Sothis. Around it are the seven planets. The nude figure {279} is the synthesis of Isis, Nephthys, and Hathoor. She is Aima, Binah, and Tebunah, the great Supernal Mother Aima Elohim pouring upon Earth the Waters of Creation. In This Key she is completely unveiled, whilst in the twenty-first she was only partially so. The two urns contain the influences of Chokhmah and Binah. On the right springs the Tree of Life, and on the left the Tree of the Knowledge of Good and of Evil, whereon the bird of Hermes alights; therefore this Key represents the restored World