Suppose a luminous sphere of radius $R_{1}$ (such as the Sun) is surrounded by a uniform atmosphere of radius $R_{2}$ and index of refraction $n$ . When the sphere is viewed from a location far away in vacuum, what is its apparent radius? You will need to distinguish between the two cases (a) $R_{2} > $ $n R_{1}$ and (b) $R_{2} < n R_{1}$ .