Calculate the fraction of the total emitted sunlight that reaches Earth. (Hint: Imagine a sphere around the Sun the size of Earth’s orbit (area = 4πa2), then calculate the fraction of that area taken up by the disk of Earth (area = πr2planet). Earth's reflectivity is 29%)

1.305 * 10⁻¹⁰

Explanation:

The earth disk is circular, hence the area of the earth disk is given as:

This ratio represents the fraction that would be blocked if the planet did not reflect any light, hence:

fraction of the total emitted sunlight reflected by earth = 29% of 4.5 * 10⁻¹⁰ = 0.29 * 4.5 * 10⁻¹⁰ = 1.305 * 10⁻¹⁰