The scientific name for the Sun is the "Sun" and its first alphabet should be capitalized. Stars are also categorized based on their temperature and their size. Based on their temperature, they are classified into O, B, A, F, G, K and M stars with the O stars being the hottest with temperatures of about 50,000 K and the M stars being the coolest with temperatures of about 3000 K. Each group is subdivided into 10 classes (eg. O0, O1,..., O9, B0, B1,...).
Based on the size and luminosity, the stars are classified into classes Ia, Ib, II, III, IV, and V. Type I stars are supergiant stars, II means giant stars, etc. Finally class V are stars called main-sequence stars which are "normal" stars (that fuse hydrogen in their cores).
Based on this notation, our Sun is a star of spectral class G2 and luminosity class V (main sequence). So the Sun is a G2V star.
Last updated on Jan. 28, 2019