The closest star to the Sun, 4.23 l.y. away, the third member of the Alpha Centauri system. It is an M5 dwarf of magnitude 11.1, but is also a flare star that undergoes sudden brightness increases of up to 1 mag. lasting several minutes; its variable star designation is V645 Cen. Intrinsically it is 20 000 times fainter than the Sun. It is thought to be gravitationally bound to the other two members of Alpha Centauri, which lie 0.09 l.y. farther away. Its orbital period around them must be a million years or more.