Photosphere Photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/"phos, photos" meaning "light" and σφαῖρα/"sphaira" meaning "sphere", in reference to it being a spherical surface that is perceived to emit light. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately 2/3, or equivalently, a depth from which 50% of light will escape without being scattered. In other words, a photosphere is the deepest region of a luminous object, usually a star, that is transparent to photons of
S-type star light, it is the sky's brightest S-type star. It has a variable late type spectrum about S6 to S10, with features of zirconium, titanium and vanadium oxides, sometimes bordering on the intermediate MS type. A number of other prominent Mira variables such as R Andromedae and R Cygni are also S-type stars, as well as the peculiar semiregular variable π Gruis. The naked-eye star ο Ori is an intermediate MS star and small amplitude semiregular variable with a DA3 white dwarf companion. The spectral type has been given as S3.5/1-, M3III(BaII), or M3.2IIIaS. S-type star An S-type star (or just