The Alpha Centauri Star System [1] - [2] - [3] Spectral Types and Sizes Alpha Centauri A is a G2 V class star like the Sun. It is a little larger than the Sun. Alpha Centauri B, a K2 V class star, is slightly smaller and cooler than the Sun. Proxima Centauri is a class M5 V Red Dwarf. Proxima Centauri is one of the smallest and dimmest types of stars. Together the Alpha AB pair emit several million times more light than Proxima Centauri. Click here for details of star spectral classes. The star sizes in the figure are based on data from the ESO Very Large Telescope Array which directly measured the size of the Alpha Centauri System stars in March 2003. This difficult feat had never before been achieved. The size of the Sun and Jupiter are shown for comparison.