It seems that the Greeks started calling it that shortly after (or
while) learning about it from the Egyptians and other nearby peoples.
That was going on during the 7th or 6th centuries BCE (600s and
500s BC) give or take a century. (The Greeks were just
emerging from a major cultural collapse, or "Dark Age", during
the two or three centuries before that time. First they came up
with Homer, and then they got interested in astronomy and
stuff.)
This probably means that the Egyptians were calling it the Dog Star
before then. The name derives from the fact that the star is set
in a constellation called the Great Dog. Many constellation names,
especially animals in the zodiac, seem to go back as far as the
time writing first came into use (around 3000 BCE, give or take a
millenium), so they may have oral histories much much older and
we'll probably never know. I don't know how old the name "The
Great Dog" is. The constellations along the zodiac probably had
names long before the constellations in the other parts of the sky.
The Great Dog is not part of the zodiac. Orion was probably named
first (but after things like Leo and Scorpio and Virgo), and then
Canis Major as an afterthought.
Sirius, by the way, means "Scorcher" and is thought to refer to
the hot weather of late summer that happens during the time of
year that Sirius rises just before Sol does. This was called
the heliacal rising, and the Egyptians used to watch for it so
they'd know in advance when the season of Nile flooding was
about to begin.
Sorry, I love star folklore, so when people ask questions like
danny's, I feel a tape yearning to unspool inside of me. ;)
(And while "dog" and "Dogon" suggest a pun in English, danny,
no one spoke English in 500 BCE. I'm assuming you were joking,
but I say this because I don't know if everyone else thinks
that.)
-- Eric Watt Forste ++ arkuat@pigdog.org ++ expectation foils perception -pcd