BIG DOG AND THE DOG STAR
The true story of the dog days, dragonflies, Saturn's rings and the days of the week.
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Photo: Michael Lustbader/Photo Researchers; Color Illustration: Jamie Leo
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The brightest stars in the constellation accompany
the sun into summer's mythic dog days.
By Fred Schaaf
Photo: Michael Lustbader/Photo Researchers; Color
Illustration: Jamie Leo
What are the "dog days" (also called the cc canicular
days;' which means the same thing)? Most people know that
they are supposed to be hot and humid days of summer. Some
folks would venture to guess that they occur in August, the
month with the greatest reputation for humidity. And many
people believe that these muggy, sultry days get their name
from the idea that dogs can go mad under such meteo
rological conditions.
The truth about the name and the exact timing of the dog
days is far more complex and interesting. The dog days are
actually named after the Dog Star, the brightest star in
the constellation Canis Major—the Big Dog—and
by far brightest star in all the heavens. The Dog Star is
more properly known as Sirius (pronounced like "serious"),
a name from ancient Greek which apparently means some thing
like "scorching." But Sirius is visible in the night sky in
winter. What would it have to do with the dog days of
summer? A star that is in the sky on winter nights is also
in the sky on summer days. Of course, even Sirius is not
bright enough to be spotted readily with the naked eye in
the midst of broad daylight. But ancient skywatchers were
able to figure out that Sirius must be accompanying the sun
across the daytime sky in the summer. And apparently as far
back as hundreds of years before Christ, one explanation of
summer's heat was that brilliant Sirius was adding extra
warmth to that of the sun at this time of year.
No one is quite sure which exact dates should mark the
start and end of the dog days. Should the central date of
the period be when the sun is passing due north of Sirius
or when they rise at the same time? The former occurs on
July 2, whatever the observer's latitude—but only in
our part of history. The latter—when the sun and
Sirius rise together depends on your latitude. From 40
degrees north latitude (Philadelphia, Denver, San
Francisco) the sun and Sirius come up together on August 4
and by August 15 Sirius rises a full hour before the sun.
(From 30 degrees, it's about a week earlier.)
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