Procyon (α CMi, α Canis Minoris, Alpha Canis Minoris) is the brightest star in the constellation Canis Minor. To the naked eye o Earth, it appears to be a single star, the eighth brightest in the night sky with a visual apparent magnitude of 0.34. It is actually a binary star system, consisting of a white main-sequence star of spectral type F5 IV–V, named Procyon A, and a faint white dwarf companion of spectral type DQZ, named Procyon B. The reason for its brightness is not its intrinsic luminosity but its relative closeness to the Sun it lies at a distance of just 11.46 light-years (3.51 parsecs) from Earth, and is therefore one of our nearest stellar neighbours. Its closest neighbour is Luyten’s Star, about 1.12 ly (0.34 pc) away, and the latter would appear as a visual magnitude 2.7 star in the night sky of a hypothetical planet orbiting Procyon.

Procyon A has a stellar classification of F5IV–V. The effective surface temperature of the star is an estimated 6,530 K, giving it a white hue. It is 1.4 times the mass, twice the radius, and 6.9 times more luminous than the Sun. Procyon A is bright for its spectral class, suggesting that it is a subgiant that has nearly fused its core hydrogen into helium, after which it will expand as “burning” moves outside the core. As it continues to expand, the star will eventually swell to about 80 to 150 times its current diameter and become a red or orange color. This will probably happen within 10 to 100 million years.

Like Sirius B, Procyon’s companion is a white dwarf that was inferred from astrometric data long before it was visited. It is more difficult to observe from Earth than Sirius B, due to a greater apparent magnitude difference and smaller angular separation from its primary. The average separation of the two components is 15.0 AUs, a little less than the distance between Uranus and the Sun, though the eccentric orbit carries them as close as 8.9 AUs and as far as 21.0 AU.

At 0.6 solar mass, Procyon B is considerably less massive than Sirius B; however, the peculiarities of degenerate matter ensure that it is larger than its more famous neighbor, with an estimated radius of 8,600 km, versus 5,800 km for Sirius B. With a surface temperature of 7,740 K, it is also much cooler than Sirius B; this is a testament to its lesser mass and greater age. The mass of the progenitor star for Procyon B was about 2.5 solar masses and it came to the end of its life some 1.7 ± 0.1 Gyr ago, after a main-sequence lifetime of 400–600 Myr. For this reason, the age of Procyon A is expected to be at least 2 Gyr.

The system contains two chthonian planets, remnants of gas giants that had their atmospheres blown away. It also has a sub-earth mildly reminiscent of Mars. A coreless planet and three ice planets round out the rest of the system. It became the home of the Republika after an initial survey had reported that the sub-Earth actually had a sustainable atmosphere and at least limited water in the form of ice. None of which proved true, but the colonists arrived before the truth was discovered.


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