USAAAO — 2026 First Round

Which of the following is closest to the ratio of the number of photons from the Sun that strike the Earth each second to the number of photons from the Cosmic Microwave Background that strike the Earth each second? (Assume the Cosmic Microwave Background to be a uniform and isotropic blackbody signal at Tc ≈ 2.725 K. As a hint, you may approximate all photons from a given source as being at the peak emission energy.)