All three members of this 'triple-star' system ... Alpha Centauri, Beta Centauri, and Proxima Centauri ... are listed as being located roughly 4.2 light-years from our solar system.
There is no single star called "alpha" or "beta". The brightest stars (usually) in each constellation are called "alpha" and "beta", followed by the Latin genitiv of the constellation; for example, "alpha centauri", "beta centauri", "alpha orionis", "alpha cruxis", etc.
Alpha Ursae Majoris (Dubhe) and Beta Ursae Majoris (Merak), which point to Polaris. (Northern Hemisphere)Alpha Centauri and Beta Centauri, which point to the Southern Cross. (Southern Hemisphere)
The term "Beta" isn't a star name -- it's a prefix that indicates that, of a group of stars, which one this one is. So there are Alpha cetauri, Beta Centauri, Gamm Centauri, etc...
There are no stars that I am aware of named "SMN". The nearest star to Earth is Proxima Centauri, and the next-closest stars are the binary pair Alpha Centauri and Beta Centauri.
The nearest other star is Proxima Centauri, at 4.2 light years away. Beyond that, Alpha Centauri and Beta Centauri are 4.5 LY away.
Alpha Centauri, Beta Centauri, and Proxima Centauri. Of the three, Proxima is the closest to us, hence the name (which means "nearest"). There is some dispute as to whether the system is actually a trinary star system, or a binary star system with Proxima as a relatively close neighbor that doesn't significantly interact with Alpha and Beta. As a result, the system is sometimes referred to as "AB Centauri", which designates a binary system.
Beta Centauri (Hadar or Agena) is the second brightest star in the constellation Centaurus and the tenth brightest star in the night sky.It has a spectral class of B1 and it is a blue-white giant star.
According to recent estimates, around 350 light years or 107 parsecs
Alpha Centauri A (Rigil Kentaurus) is a type G2V star - which is the same as our Sun so it has a colour of yellow.Alpha Centauri is abinary star system.Alpha Centauri A - the primary star, is a G2V star so has the apparent colour of yellowish-white, the same as our Sun.Alpha Centauri B - the secondary star, is a K1V star so has the apparent colour of yellow-orange.
B Centauri (B Cen) is a star in the constellation Centaurus.It is an orange giant with a spectral class of K3.
Hadar (Beta Centauri) is actually three stars. They are very close together and hence appear as one.