When I was a kid I would hear that it is "the dog days of summer" in Texas during times of persistently hot weather in the summer. I assumed that the term dog meant that outdoor dogs suffered from all the heat day after day. Life for an outdoor dog just can not be fun on those 95 F and hotter days that repeat in the summer.
To my surprise I learned several years later that the term had nothing to do with real outdoor dogs but rather dealt with a Star in the constellation Canis Major that is one of the brightest stars in the sky and is approximately 8.6 light-years distant from Earth. The Dog days is named after Sirius, the Dog Star. The Dog days come when the Dog Star begins to line up with our Sun (lining up is called conjunction). It was thought long ago that when the Dog Star aligned with the Sun that they combined their energy to make the weather even hotter. Of course, we now know that no Star would warm the earth at even the smallest fraction that the Sun does since stars are very far away.
However, the term stuck. In July and August the background of stars beyond the Sun includes the Dog Star Sirius. In July and August during a persistent heat wave, do not be surprised to hear, "we are in the Dog days of summer".