Hobbies And Interests
Magnitude
The scale that measures an object's visual magnitude is based on a system devised by the Greeks and modified by modern astronomy; one full number on the scale is approximately 2.5 times brighter than the next. On this scale the sun has a magnitude, or brightness, of minus 26 while the full moon registers at minus 11. Planets such as Venus, Jupiter and Mars all have negative magnitudes as well. Sirius is easily the brightest star in the evening heavens, with the runner up being Canopus, which comes in with a magnitude of minus .72. The human eye can detect stars that have a magnitude as faint as plus 6, but anything less cannot be seen without optical aid such as binoculars or a telescope.
The Dog Star
Sirius is best viewed in the United States during the winter months. It rarely gets very far from the horizon but is easy to spot, especially if one uses the constellation Orion as a guide. Orion has three stars in his "belt" which, when followed downward, point right to Sirius. Orion is a hunter according to myth and Canis Major is one of his hunting dogs. This gave Sirius the nickname of "The Dog Star" and in the constellation itself Sirius marks the dog's heart.
Distance
In relation to the Earth's Sun, Sirius is about 23 times brighter. It is two times larger than our star but it in no way an above average star in terms of brightness when viewed from other points in space. The reason Sirius is so bright from the vantage point here on Earth is that it is the fifth closest of all the stars to this planet. It is "just" 8.5 light years away, meaning that at the speed of light--186,000 miles per second--it takes the light emanating from Sirius 8.5 years to reach an observer on Earth. Canopus, for perspective, is an astounding 316 light years away and still is the second brightest star in the celestial sphere. Canopus is nearly 15,000 times brighter than the sun.
Double Star
In reality Sirius is what is known as a double star. It is a binary system of two separate stars, which is not at all uncommon, as one star orbits the other. Sirius A is the brighter by far of the pair while Sirius B was found to be a collapsing white dwarf star, about the size of our Earth. Having used up all of its hydrogen this star is imploding over time and becoming incredibly dense. The companion star to Sirius was discovered by an astronomer named Alvan Clark in 1862 after a German astronomer, Friedrich Bessel, observed strange movements of Sirius from nightly observations that led him to believe it had to be a double star.
The Winter Circle
Sirius is part of what astronomers call the "winter circle" although the shape is much more elliptical in nature. Using some of the brightest stars in the winter sky an observer can trace an oval outline in the sky. Starting with Sirius and proceeding clockwise, the stars Procyon in Canis Minor, Castor and Pollux in Gemini, Capella in Auriga, Aldebaren in Taurus and Rigel in the "foot" of Orion comprise this oval.