The Northern Hemisphere officially welcomes—or greets, anyway—the dog days of summer today. This period of hot sultry weather is heralded by the heliacal rising of a certain star, that is, by the first rising of a star after its apparent disappearance (due to conjunction with the sun). (来源：www.EnglishCN.com)

The ancient Egyptians worshiped that star as Sothis, and associated its rising with fecundity of the fields (which followed the annual flooding of the banks of the Nile around this time). The Egyptians also marked the start of the new year with the sighting of Sothis.

The Greeks referred to that same star as Seirios, meaning "scorching" or "burning," a reference not to the fact that Sirius shines so brightly, but to the rising temperatures surrounding its return. When the Greeks applied their mythology to the constellations, Sirius was pictured as the hound dog of the hunter Orion.

That leads us to the Romans. They called Sirius canicula, or "small dog," and the constellation containing it, "Greater Dog." They dubbed the hot days that seemed to come with the star dies canicula—literally, dog days—a phrase translated and borrowed into English early in the 16th century.

Stay cool and keep in touch.