What is the origin of the idiom "dog days" and when to use it?

The origins of the phrase "dog days" can be traced back to ancient Greece and Rome, where it was believed that the star Sirius, also known as the "Dog Star," rose in conjunction with the sun during the hottest part of the summer. This period was associated with drought, sickness, and other hardships. Today, the phrase "dog days" is often used to describe a period of hardship or adversity, whether it be personal or societal.