We frequently use the phrase “dog days of summer” to talk about the sweltering heat that occurs in July through August, which is generally the hottest part of the year in the Northern Hemisphere. This term has astronomical origins.
Ancient Romans observed that Sirius, the “Dog Star” located in the constellation of Canis Major (the Big Dog), rises and sets in close conjunction with the sun—Sirius used to appear even nearer to the sun in ancient times. At an apparent magnitude of -1.46, Sirius is the brightest star in the night sky.
When Sirius was up in the sky, the Romans noticed how hot the summers were. Their conclusion was that the heat from Sirius added to that of the sun’s, so the star was responsible for the hottest time of the year.
The name Sirius is of Greek origin and means “scorching,” and the star is about twice as massive as our sun. Sirius is actually a binary star system, meaning that two stars, Sirius A and its much fainter companion Sirius B, orbit around a common center of mass.
