Why are they called the "dog days" of summer?
First, the present time of sweltering is not to be confused with Suede's classic album, Dog Man Star, although if in fact we are the pigs, it's worth noting that the Chinese constellation called 奎 (Legs; in the European tradition Andromeda/Pisces) might alternatively be viewed as a wild boar rather than a tiger.
Because: The "dog days" phrase goes back to ancient Greece and Rome, and refers to the dog star.
Read all about it here:
Why Do We Call Them the 'Dog Days' of Summer? by Becky Little (National Geographic)
... Originally, the phrase actually had nothing to do with dogs, or even with the lazy days of summer. Instead, it turns out, the dog days refer to the dog star, Sirius, and its position in the heavens.
To the Greeks and Romans, the “dog days” occurred around the day when Sirius appeared to rise just before the sun, in late July. They referred to these days as the hottest time of the year, a period that could bring fever, or even catastrophe.