Canis Major and Canis
Minor
are customarily associated
with the great hunter, Orion, as his hunting dogs, following him
obediently across the sky. Each of the constellations has but
a single notably bright star: Sirius, the Dog Star, is well known
as the brightest star of all (3½ times as bright as Arcturus,
second ranked among northern hemisphere stars); and Procyon, the
Before-Dog star, is well known, too, because it rises above the
horizon just before Sirius does. Both of these stars are binary
double stars, each with a white dwarf companion. Both are relatively
close, 8.7 light years for Sirius, and 11 light years for Procyon.
In fact, the only stars closer to the Sun than Sirius can be seen
only from southern skies. Sirius has a diameter twice that of
the Sun, while its companion Sirius B is tiny, only about three
Earth-diameters in size, but nearly as massive as the Sun, many
thousands of times as dense as either Sirius or the Sun. This
interesting companion star was discovered in the year 1862 by
the renowned telescope maker Alvan Clark while he was testing
a new 18-inch refractor pointed at Sirius. It had previously been
predicted that Sirius had a binary partner after the discovery
in 1834 of a strange irregularity in its position. Although Sirius
B is a respectable 8.4 magnitude star, its closeness to the brilliant
Sirius makes it nearly impossible to detect with a telescope of
less than 10 inches of aperture.
Sirius and Procyon are two of the stars that comprise the Winter
Oval asterism. Some refer to this group of first magnitude stars
as the Winter Hexagon, counting Pollux and Castor as a single
corner of the shape. For those who may be unacquainted with this
idea, the other stars, clockwise from Sirius and Procyon, are
Pollux and Castor in Gemini, Capella in Auriga, Aldeberan in Taurus,
and Rigel in Orion. A variant of this idea adds Bellatrix and
Betelgeuse to this group, but omits Aldeberan, to form a giant
figure 6 signaling a right ascension of 6 hours.
In the mythology of ancient Egypt, Osiris and Isis descended to
the earth to bless the inhabitants. Isis showed them how to grow
wheat and barley, and Osiris taught agriculture and also gave
men laws and promoted the worship of the gods. He made the valley
of the Nile a happy country, then he left his wife Isis in control
of the government and set out to continue his good works in other
lands. He conquered nations everywhere with music and eloquence,
not with weapons. His brother Typhon became envious and plotted
to kill Osiris through a malicious conspiracy. When Isis heard
of the cruel murder she wept such tears that the Nile rose and
overflowed its banks. From that time forward the annual rising
of the Nile brought the life-giving renewal of fertility to the
valley. Above, the star Sothis was identified with Isis, and this
brilliant star (Sirius) was welcomed each year to herald the Nile
flood. The day when it first was visible before dawn marked New
Year’s Day, the most important day of the year. Temples erected
to Isis were oriented to the exact spot where Sothis would rise.
Sothis was the leader of 36 stars, called the Deccans, that followed
each other at intervals of ten days throughout the year. By the
heliacal rising of these stars, the Egyptians kept track of their
calendar, adding five days to complete the year.
Of objects for viewing with binoculars in Canis Major and Canis
Minor there are few. M41 is a beautiful open star cluster containing
about a hundred stars. It is just visible to the naked eye and
is just south of Sirius by four degrees. Stars of several different
colors including some very red stars are in the field. R Canis
Majoris is a variable star with a very short period, doubling
its brightness from magnitude 6.7 to 5.9 in 27 hours. There are
also some pretty double stars including the orange and pale blue
h3945. Mu-Canis Majoris is a white-blue quadruple star.