In the ancient world, the constellations of Orion and Canis Major (especially the Dog Star, Sirius) were calendar markers for planting and reaping. Sirius, the Dog Star, sets in the west in spring and is absent from the sky for seventy days, then its heliacal (just before dawn) rising in the east marked the beginning of the Dog Days when the sun was said to burn at its most fierce and rainfall to be at its lowest level. The Old Farmer’s Almanac of 1792 lists the timing of the Dog Days as the days beginning July 3rd and ending on August 11th (Old Lughnasa), and they are traditionally listed as such in the present day. They are a period of desiccating heat, when summer growth and moistness ends, and the sun dries the corn ready for harvesting, ushering in the Autumn and the gathering of the First Fruits.
Sirius (‘Scorching Star’) is the brightest star in the sky, and lies in the constellation of Canis Major, the ‘Greater Dog’ which, along with Canis Minor the ‘Little Dog’, follows the constellation of Orion the hunter across the sky, helping him pursue Lepus the Hare or confront Taurus the Bull. Canis Major has been associated with dogs from the earliest times. The ancient Assyrians called the Dog Star the ‘Dog of the Sun’ or ‘Star Dog of the Sun’. The Assyrian month of Abu (July-August) signified ‘fiery hot’ because the sun was in Leo and therefore raging like a lion.
The Romans sacrificed a red-coloured dog in May, when Sirius disappears for seventy days below the western horizon, to ensure the health of the forthcoming crops. The hottest part of the year, which dried the grain ready for harvesting, they called the dies cani cultriac or ‘Dog Days’. They thought that Sirius was a distant sun (the central sun of the Milky Way, in fact) which during the Dog Days rose with our sun to add its own heat, making the weather unbearable. Its influence was considered baneful and malign. Pliny wrote that Sirius burned with “…a bright fire and sheds a killing light’ and went on to say that ‘this is the constellation which has the most widespread effects on earth. At its rise the seas are rough, wine in the cellars bubbles, marshes are stirred.”  Aristotle said “…this is a period of great upheaval when the sea is extremely rough and amazing catches are made, when fish and mud rise to the surface.” 
Hesiod described it as ‘a desiccating sun’, burning up plants and making the seeds in the earth sterile by depriving them of food. Animals die of thirst, vines are burned and humans are prostrated with fevers and illness, especially siriasis (a type of meningitis which attacks young children). According to these ancients, the Dog Days are a time of cruel heat when men’s skins are burned and their throats parched with thirst. Those afflicted with hydrophobia were said to have been driven mad by Sirius. In fact, the Greeks imagined the constellation of Canis Major in the form of a rabid dog with its tongue lolling and its eyes bulging. The astronomer Manilius said: “…such is the heat diffused among the constellations, and everything is brought to a halt by a single star.” He went on to relate how the heat brought out the worst in people, with anger, hatred and fear, impetuosity, frayed tempers and arguments, all fanned by alcohol.
It was during this time that the Adonia Festival was celebrated in Greece, as Theophrastus said ‘when the sun is at its most powerful’. During the festival women would plant small gardens – called Gardens of Adonis and dedicated to the vegetation god – in clay pots or wicker baskets. These were composed of wheat, barley, fennel and lettuces. The women would climb ladders up to their rooftops, thereby placing the little gardens as close to the sun as they could. During this time of year the great heat gives an impetus to a plant’s growth, but this can become leggy and spindly with the plant outgrowing its strength, while young shoots wither in dryness. The gardens were left to grow for only eight days to come to maturity, in contrast to the eight months taken by the cereal crop under the auspices of the goddess Demeter. At the culmination of the festival the gardens were taken from the roofs and cast in to the sea or into springs. Thereafter August was sacred to the goddess Demeter and her daughter Persephone.
In Norse myth the Dog Star Sirius is called Lokabrenna (‘the Burning of Loki’ or ‘Loki’s Brand’). Sif was the wife of Thor, the god of thunder. She had beautiful golden hair until Loki cut it all off for a prank. Thor was so angry that he wanted to kill the trickster, but Loki was able to persuade the dwarfs to make some magical hair for Sif, which once it touched her head, would grow like her own hair. It is clear that Sif’s hair is the golden corn, which is cut and regrows with the next year, making her a corn or harvest goddess. Her husband is the thunder god who brings the fertilizing rain to the earth in the summer, to make the corn grow. Loki, usually described as a god of wildfire and heat, is associated here with Sirius and the heat of the Dog Days, which causes the ripening and subsequent cutting of the grain.
The Feast of St. Christopher falls on 25th July. He is the patron saint of travellers, portrayed in the Eastern Church as a man with the head of a dog. He has two festivals on May 9th (in the Eastern Church) and July 25th (in the Western church) and these dates correspond to the setting and rising of Sirius, the Dog Star. This suggests an interesting Pagan origin for the Christian saint who carried the Christ Child across a raging river in a storm, and thus he became the patron of travellers who often wear St Christopher medals for protection.
In ancient Egypt, Sirius was the main seasonal marker which mobilised the whole calendar.  In contrast to elsewhere, the Egyptians thought its heliacal rising after its absence from the sky for seventy days brought the Nile inundation, the annual floods which carried rich alluvial mud for planting, and began the Egyptian year in the month Wep-renpet, ‘Opener of the Year’. They thought of Sirius as a feminine sun which added its own power to the usual sun, and the festivities at the Temple of Hathor in Dendera were chiefly concerned with the birth of this new sun. People would gather on the roof of the temple to see her rise with the sun Ra, sitting on the prow of his solar boat and uniting her rays with his as they melted into the dawn light. The Egyptians called the star Septit  (or Sothis in the Greek form), titled ‘the Water Bringer’ and identified it with Isis. During the festivities at Dendera, a statue of Isis/Hathor was carried up to the roof to face Sirius and the rising sun. Isis appears in the Pyramid Texts as the chief mourner for her husband, the vegetation god Osiris (identified with the constellation Orion), whom she brought back to life with magic. The rising of Sothis was considered to be the goddess coming to mourn her husband and revive him (as corn god) with the flooding of the Nile.
Sirius disappears from the sky for seventy days before its heliacal rising. This marked its death and rebirth and re-started the calendar. The Egyptians noted that every ten days one of the thirty six decans (the stars that kept the calendar, chosen because they followed the same pattern as Sirius) disappeared into the west and remained unseen for a period of time before reappearing with the dawn in the east. As one ‘died’ another was ‘reborn’ every ten days, according to Papyrus Carlsburg 1. During the period the star was missing, it was said to have entered the Duat (‘Embalming House’) or netherworld, where its impurities were shed, preparing it for rebirth.  The Egyptian mummification process took seventy days, the period of time the decans spent in the Duat.
Of all the stars only the heliacal rising of Sirius coincides with the length of our solar year of 365.25 days. Each year it started time – and therefore order, the seasons and creation – and because of this it was sometimes linked with the benu bird of creation. The benu had alighted on the primordial mound which had emerged from the elemental waters, the only place not submerged and when it flew away, the sun rose for the first time and brought light and life to the world, just as the heliacal rising of Sirius did each year. The Greeks identified the benu with the phoenix. Tacitus (1st century CE) reported that it took 1461 years for the benu to fly to the east and back. This was because the Egyptians calculated that Sothis took 1461 years to recycle through their 365 day calendar, moving forward by a day every four years (which accrued because they had no leap year). This was called a Sothic Year.
© Anna Franklin, heavily condensed from Lughnasa, History, Lore and Celebration by Anna Franklin, Lear Books
 Pliny, Natural History. II
 Aristotle Hist. An.
 Hydrophobia is better known as rabies, one of the symptoms of which is a blazing thirst but a fear of water.
 Marcel Detienne, The Gardens of Adonis, Princeton University Press, 1977
 Dr. E.C. Krupp, Beyond the Blue Horizon, Oxford University Press, Oxford, 1991
 A Greek form of her Egyptian name Aset or Eset, meaning ‘throne’.
 Dr. E.C. Krupp, Beyond the Blue Horizon, Oxford University Press, Oxford, 1991