The Wednesday Morning Math Challenge: Week 10

Welcome to Week 10 of the Wednesday Morning Math Challenge. You can find solutions to the Week 9 puzzles here, along with — more importantly — discussions of some ways to approach them. Remember that the real goal here is to think creatively.

This week, I’m going to pose a thought experiment that was proposed to me last week. Someone asked me how many stars are behind the moon.

Now, this is a very tough question, and arriving at an answer requires a lot more than basic mathematics. But if we simplify the question and use some understandably rough numbers and assumptions, we can get a pretty reasonable estimate.

I’m going to tell you a few things that we are going to take to be true. First, there are 100 billion stars in the Milky Way, and they’re evenly distributed around the earth. Next, the moon is 385,000 kilometers away from the earth. And, finally, the moon has a radius of 1,700 kilometers.

My question to you is: How many stars in the Milky Way are hiding behind the moon?