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The Dog Star
Sirius is the brightest star in constellation Canis Major and the brightest star in the northern hemisphere. Magnitude of -1.47. Located in the constellation Canis Major. Sirius can be seen from almost every inhabited region of the Earth's surface (those living north of 73 degrees cannot see it) and, in the Northern Hemisphere, is known as a vertex of the Winter Triangle. Ancient Egyptians were aware of Sirian binary or double star system in predynastic times, before 3200 BC. Five thousand years later, in 1862 modern astronomy rediscovered The system of Sirius contains two known stars, the first binary star system discovered, consisting of a bright white main sequence star of spectral type A1V, named Sirius A, and a faint white dwarf companion of spectral type DA named Sirius B. Sirius B is a white dwarf star (one with the mass of our sun, packed into a sphere roughly four times that of the earth Sirius B traces an elliptical orbit around Sirius A, and their common center of gravity, directly face onto the Earth like the dial of a clock. Taking 50 years to complete their orbit, the period of closest connection, called the periastron, is a time when the radiated energies of these two great stars is especially intense. Sirius B spins on it's axis at an incredible 23 times a minute (23 rpm!!), generating an enormous magnetic field. As it approaches periastron, it begins to pull huge amounts of gas and material away from its less dense companion. Vast amounts of electromagnetic radiation, including visible light, ultraviolet, X-rays, gamma rays and beyond, are thrown into space. The extra gas and material Sirius A provides for her companion re-ignite fusion reactions within Sirius B Under the right conditions, Sirius can be observed in daylight with the naked eye. Ideally the sky must be very clear, with the observer at a high altitude, the star passing overhead, and the sun low down on the horizon. Sirius B, a white dwarf star that has a surface temperature of about 25,000 degrees Celsius which produces very low energy X-rays. The dim source at the position of Sirius A – a normal star more than twice as massive as the Sun – may be due to ultraviolet radiation from Sirius A leaking through the filter on the detector. In contrast, Sirius A is the brightest star in the northern sky when viewed with an optical telescope, while Sirius B is 10,000 times dimmer. Because the two stars are so close together Sirius B escaped detection until 1862 when Alvan Clark discovered it while testing one of the best optical telescopes in the world at that time. The theory of white dwarf stars was developed by S. Chandrasekhar, the namesake of the Chandra X-ray Observatory. The story of Sirius B came full cycle when it was observed by Chandra in October 1999 during the calibration or test period. The white dwarf, Sirius B, has a mass equal to the mass of the Sun, packed into a diameter that is 90% that of the Earth. The gravity on the surface of Sirius B is 400,000 times that of Earth! Sourced from various internet sites |
