Earth’s penumbra: This is a continuation of Exercise 17. Earth also has a partial shadow known as the penumbra. The penumbra is represented in Figure 3.40. The penumbra has a radius of about 10,000...

Earth’s penumbra: This is a continuation of Exercise 17. Earth also has a partial shadow known as the penumbra. The penumbra is represented in Figure 3.40. The penumbra has a radius of about 10,000 miles at a point on the opposite side of Earth from the sun and at a distance from Earth equal to the moon’s distance from Earth. The penumbra has a conical shape and, if extended toward the sun, would reach an apex shown in Figure 3.40. How far away from Earth is this apex?