Critters 101:        The Dog Days of Summer
Everyone knows that the “dog days of summer” occur during the hottest and muggiest part of the
year.  Webster defines “dog days” as the period between early July and early September when the
hot sultry weather of summer usually occurs in the northern hemisphere.  But where does the term
come from?  Why do we call the hottest days of summer “dog days?”

In ancient times, when the night sky was unobscured by artificial lights, people drew images in the
sky by connecting the dots of stars.  These star pictures are now called constellations, and the
constellations that are now mapped out in the sky come from our European ancestors.

They saw images of bears (Ursa Major and Ursa Minor), twins (Gemini), a bull (Taurus), and others,
including dogs (Canis Major and Canis Minor).  The brightest of the stars in Canis Major (the big
dog) is Sirius, which also happens to be the brightest star in the night sky.  It is so bright that the
ancient Romans thought that the earth received heat from it.

During late July, the Dog Star rises and sets with the sun.  They named this period of time, from 20
days before to 20 days after, “dog days” after the Dog Star.  Today, dog days occur during the
period between July 3 and August 11.  Although, it is certainly the warmest period of the summer,
the heat is not due to the added radiation from a far-away star, regardless of its brightness.  No, the
heat of summer is a direct result of the earth’s tilt.