The full flag featuring the sun is called the Official Ceremonial Flag (Spanish: Bandera Oficial de Ceremonia). The flag without the sun is considered the Ornamental Flag (Bandera de Ornato). While both versions are equally considered the national flag, the ornamental version must always be hoisted below the Official Ceremony Flag.
In the center stripe there is an emblem known as the Sun of May (Spanish: Sol de Mayo), a golden sun. The Sun is modeled after the symbol of Inti, the Incan god of the Sun. 1source: wikipedia