Origin of shrine's name:

Alpha Centuri (also known as Rigil Kent) is one of the closest stars (minus the sun) to us, about 4.2 light years away. It is the brightest star in the constellation Cenaurus as well as in the southern hemisphere.
Note: although there is no direct relation to Mercury, by the name Alpha one could relate it to the first senshi to join Sailor Moon.

Relations to Mercury:

Hermes, Grecian counterpart to the Roman god Mercury. Hermes is the mythical messanger of the gods, who also led people to Hades.