That's when David joined the Sloan Digital Sky Survey at the nearby Apache Point Observatory.

We had the sense that it was going to be this great thing that was starting, but it hadn't actually started yet.

What we wanted to do was something much more ambitious and actually get a map of the million brightest galaxies on the sky.

The task required measuring the distance, and therefore redshift, for every single one of these galaxies.

Obviously, you need to look at more than one galaxy at a time, so that's the trick.

And if you were a futurist you'd say, "Well, it's the 1990s, we have computers and we have robots."

The folks designing the Sloan, though, decided to take the pragmatic approach and say, well, we actually want this thing to work.

Instead of robots, the ingenious system they came up with required a far more human touch.

And they would have to go round the universe not once, but twice.

It's really doing two maps of the sky.