It is the destination most requested by his human companions. Doesn't matter what century they're from. It used to annoy him. Idiot humans! Offer them the Universe, and what do they want to see? Two blokes bouncing around for a bit.
It was Wilf who made him understand. "'It's like watching a home movie of a baby walking for the first time. And you think, 'That was me. That was when I started to grow up.'"
So here he is once more, and seeing the wonder in Bethany's eyes makes it all new again.
"... a giant leap for mankind."