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"Sirius is so bright because it is in fact a binary star system, two stars orbiting each other"
Well no. It is the brightest star because it is so close to us and burns at 25000K or so. Alpha Centaurii is 4.4 Ly away but a G class star, 6000K, much cooler and less intrinsically bright than Sirius.
That is why astronomers mathematically push stars to 32.6 Ly away, to give the "absolute magnitude", to even things out a bit.
Stu
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