Sirius , the seventh-nearest stellar system , is a visual binary containing the metallic-line A1 V star Sirius A , brightest star in the sky , orbited in a 50.13-year period by Sirius B , the brightest and nearest white dwarf ( WD ) . Using images obtained over nearly two decades with the Hubble Space Telescope ( HST ) , along with photographic observations covering almost 20 years , and nearly 2300 historical measurements dating back to the 19th century , we determine precise orbital elements for the visual binary . Combined with the parallax and the motion of the A component , these elements yield dynamical masses of 2.063 \pm 0.023 M _ { \odot } and 1.018 \pm 0.011 M _ { \odot } for Sirius A and B , respectively . Our precise HST astrometry rules out third bodies orbiting either star in the system , down to masses of \sim 15– 25 M _ { Jup } . The location of Sirius B in the H-R diagram is in excellent agreement with theoretical cooling tracks for WDs of its dynamical mass , and implies a cooling age of \sim 126 Myr . The position of Sirius B in the mass-radius plane is also consistent with WD theory , assuming a carbon-oxygen core . Including the pre-WD evolutionary timescale of the assumed progenitor , the total age of Sirius B is about 228 \pm 10 Myr . We calculated evolutionary tracks for stars with the dynamical mass of Sirius A , using two independent codes . We find it necessary to assume a slightly sub-solar metallicity , of about 0.85 Z _ { \odot } , to fit its location in the luminosity-radius plane . The age of Sirius A based on these models is about 237–247 Myr , with uncertainties of \pm 15 Myr , consistent with that of the WD companion . We discuss astrophysical puzzles presented by the Sirius system , including the probability that the two stars must have interacted in the past , even though there is no direct evidence for this , and the orbital eccentricity remains high .