La Superba (Y CVn, Y Canum Venaticorum) is a strikingly red giant star in the constellation Canes Venatici. It is a carbon star and semiregular variable. Visibility La Superba is a semiregular variable star, varying by about a magnitude over a roughly 160-day cycle, but with slower variation over a larger range. Periods of 194 and 186 days have been suggested, with a resonance between the periods. Y CVn is one of the reddest stars known, and it is among the brightest of the giant red carbon stars. It is the brightest of known J-stars, which are a very rare category of carbon stars that contain large amounts of carbon-13 (carbon atoms with 7 neutrons instead of the usual 6). The 19th century astronomer Angelo Secchi, impressed with its beauty, gave the star its common name, which is now accepted by the International Astronomical Union. Properties The angular diameter of La Superba has been measured at . It is expected to be pulsating but this has not been seen in the measurements. At , this corresponds to a radius of . If it were placed at the position of the Sun, the star's surface would extend beyond the orbit of Mars. La Superba's temperature is believed to be about , making it one of the coolest true stars known. It is faintly visible to the naked eye, and the red colour is very obvious in binoculars. When infrared radiation is included, Y CVn has a bolometric luminosity several thousand times that of the Sun. The mass of this type of star is difficult to determine; it would initially have been around and somewhat less now due to mass loss. An estimate from Jim Kaler gives the star a luminosity between and radius between based on an assumed temperature of 3,000 K, and the author then classified it as a C7 or CN5 supergiant star although its mass is too low to be a true supergiant. Observations in the 60 and 100 micron infrared bands by the IRAS satellite showed that Y CVn is surrounded by a dust shell 0.9 parsecs in diameter. This is one of the most prominent circumstellar dust shells detected in the IRAS all-sky survey. Evolution After stars up to a few times the mass of the sun have finished fusing hydrogen to helium in their core, they start to burn hydrogen in a shell outside a