9) A large converging (i.e. concave) mirror is used as a telescope. (a) If it focuses the image of a star at a distance of 5 m from the vertex of the mirror, what is the approximate radius of curvature of the mirror? (b) If we use the telescope to image a star that 1.0×10¹⁵ m from us that has radiant power of 3.0×10²⁶ W, then what is the irradiance at the location of the telescope? (The surface area of a sphere is 4πr². This is why astronomers crave big glass!!.