Look up at the moon for today's Geo Quiz.

It was 40 years ago tomorrow that Apollo 8 did something that was never done before. It orbited the moon.

Bill Anders was one of the three astronauts on board. It was an experience that moves him to this day.

"When I look up at the moon, particularly when it's just a little bit of a sliver on the right side that's illuminated, it give me a little chill in my back because that's the way it looked when we went, and let me tell you, the moon is one heck of a long way off!"

Of course, from the moon, it's the Earth that's "one heck of a long way off." During the Apollo 8 mission Anders took a dramatic photo of the Earth rising against the black sky of space.

One of our planet's geographic features that caught his eye from space was a bright blue and deep oceanic trench. This Atlantic channel near the Bahamas is 6,000 feet deep. From the moon, it looks a little like, dare we say it, a stuffed Christmas stocking.

So can you name it?