CANIS MAJOR

The Big Dog

Canis Major - Alexander Jamieson - 1822

Following faithfully at Orion's heels is Canis Major, the big dog. It is a constellation that has had a lot of attention throughout history from cultures all over the world, and rightly so, because it contains far and away the brightest star in the entire night sky: Sirius, the Dog Star. With a magnitude of -1.46, it is more than twice as bright as the next brightest star, Canopus (magnitude -0.72).

Sirius

In ancient Egypt, Sirius was revered as the Nile Star, or the Star of Isis. Throughout the winter and spring, Sirius rises four minutes earlier each night (as all stars do), until by the summer solstice (June 22) it is rising just before dawn. Some Egyptian temples were aligned with window openings facing east directly where the Dog Star rose, and when the light from the star shone through the opening, it meant the Nile was about to commence its annual flood, spreading its waters and rich soil over the adjoining floodplain , an occurrence critical to the survival of the Egyptian people. Some ancient Mayan temples as well were aligned with Sirius, as it signaled the advent of the all important rainy season.

By the time the hot days of July and August arrive, Sirius is rising with the Sun, and the dog days of summer are upon us. In ancient times it was thought the energy of Sirius combined with the Sun at this time, and the star was blamed, in the words of Robert Burnham Jr., for "bringing forth fever in men and madness in dogs." Dante spoke of "the great scourge of days canicular". Virgil wrote, "the Dog Star, that burning constellation, when he brings drought and diseases on sickly mortals, rises and saddens the sky with inauspicious light". Even in Homer's Illiad, we read of the wrathful Achilles "blazing as the star that cometh forth at Harvest-time, shining forth amid the host of stars in the darkness of the night, the star whose name men call Orion's Dog. Brightest of all is he, yet for an evil sign is he set, and bringeth much fever upon hapless men..."

The name Sirius is Greek for scorching. It is an A1 main sequence star, 1.8 times the diameter of the Sun. The reason it is so bright is because it is so close, only 8.7 light years away, the fifth closest star to Earth. Because Sirius is so bright, when it is close to the horizon, it puts on quite a show, atmospheric refraction turning it into a wild kaleidoscope of dazzling, sparkling colors.

Extra-solar Planets

Canis Major contains five stars that are known to support planetary systems. One of these stars is bright enough to be seen with the naked eye. The star is designated HD 47536, and its location is shown on the image above. Two gas giants have been discovered orbiting the star, but there could be other, smaller planets we have not yet been able to detect. Another star, HD 47186, also noted above, is much fainter, and lies at the limits of naked eye visibility. It is, however, easily found in a backyard telescope, and the two planets found in its system are much closer to the size of Earth. For more information, go to NASA's Planet Quest.

Mysteries of Sirius

Although Sirius is unmistakably blue/white in colour, nearly all ancient texts refer to it as red. Some suggest that colours were sometimes interpreted differently in ancient times. But another possible explanation surfaced with the 1862 discovery of a tiny companion star to Sirius, named Sirius B, or the Pup. It is a white dwarf star, and a white dwarf is the evolutionary descendent of a red giant, leading to the speculation that in ancient times it was in fact a red giant that overshadowed Sirius, accounting for the red colour. The problem is that it should normally take at least 100,000 years for a red giant to become a white dwarf, so it's a mystery. The extraordinary photo below of Sirius and its pup (lower left) was captured by the Hubble Space Telescope in 2003.

The Dogon tribe of Mali, Africa, have tribal traditions that include the knowledge of Sirius B, the tiny companion star that is impossible to see without the largest of telescopes. They also know that it orbits Sirius every 50 years, and that it is extremely dense, and heavy. They also possess the knowledge of many other astronomical facts completely inconsistent with a primitive tribe in the darkest jungles of Africa. There is no record of early missionaries visiting them and imparting them with this knowledge, although the possibility cannot be ruled out. The popular and more exciting (albeit fanciful) theory is that sometime in their past the Dogon tribe acquired this information when they were paid a visit by extraterrestrials...

M41

Just below Sirius is the bright open star cluster M41, visible to the naked eye, and a favorite target for backyard telescopes.

M41 (95K)

Alphabetical Links to the Constellations

ANDROMEDA AQUARIUS AQUILA ARIES AURIGA BOOTES CAMELOPARDALIS CANCER CANES VENATICI CANIS MAJOR CANIS MINOR CAPRICORNUS CARINA CASSIOPEIA CENTAURUS CEPHEUS CETUS COLUMBA COMA BERENICES CORONA AUSTRALIS CORONA BOREALIS CORVUS CRATER CRUX CYGNUS DELPHINUS DORADO DRACO EQUULEUS ERIDANUS FORNAX GEMINI HERCULES HYDRA LACERTA LEO LEO MINOR LEPUS LIBRA LUPUS LYNX LYRA MONOCEROS OPHIUCHUS ORION PEGASUS PERSEUS PISCES PISCIS AUSTRALIS PUPPIS SAGITTA SAGITTARIUS SCORPIUS SCULPTOR SCUTUM SERPENS SEXTANS TAURUS TUCANA URSA MAJOR URSA MINOR VIRGO VULPECULA