Roughly corresponding to the sun being Leo, the searing heat of this time of summer. From the Dog Star Sirius returning to rise over the pre-Dawn horizon which for the Egyptians occurred in early July & heralded the flooding of the Nile & the return of fertility.
The Dog Star’s connection to dogs was not only maintained by constellations and mythology, it was boosted by the fact that dogs seemed to take the brunt of the dog days. They suffered from the heat more intensely than humans seemed to, and were at greater risk of madness.