Jeffrey Andrews-Hanna

And specifically, that's the night side of the moon covering up the sun.

And if you look closely, even in the lighting in this room, you can actually see details on the night side of the moon.

If I stretch the contrast more,

That looks just like a full moon because it's the same face of the moon that we see normally.

But what's lighting it up if the sun is behind the moon?

This is the moon illuminated in earth shine because just like a full moon really lights up the earth, a full earth really lights up the moon.

And in fact, you don't have to wait for a solar eclipse to see this.

If you go out in a week or so and look at a crescent moon, if you look carefully, you'll notice you can actually see the unilluminated hemisphere of the moon, the night side of the moon,

you can see that lit up in earth shine.

So I would argue there really isn't a dark side of the moon, at least not in the sense of a permanently dark unknown side of the moon, unless of course you think about it this way.

Light that we see, visible light,

only penetrates about 1 1,000th of a millimeter into the lunar surface, about a micrometer.

What that means is that all of our cameras and our eyes from Earth are only seeing the very, very, very topmost surface of the moon.

That leaves the entire vast interior of the moon unseen, at least unseen in the traditional sense.

So pictures are only skin deep.

If there's a dark side of the moon, it's the inside of the moon.

But unlike the sort of metaphorical dark side of the moon, the inside of the moon is not a complete unknown.

We can say things about it.

So we have a few different ways that we can probe the inside of the moon.

One approach is using radar.