Will Oxley

And then we use a device called a sextant, which essentially measures angles.

In the olden days, they were called a quadrant and it has a series of mirrors and essentially the mirrors are split in half.

And what you're trying to do is through one half, you're looking at the horizon and then the other half of the mirror, you're trying to have the heavenly body that you're looking at.

And the idea is that you bring that heavenly body down to the horizon and

And you measure the angle.

And so by knowing the angle from that body to the horizon, and then a number of other mathematical calculations, you can determine that you're somewhere on a big circle, somewhere on the earth.

And of course, that circle is so large that for the purposes of navigation, you can turn that circle into a straight line.

So when you take a site, you know, you're somewhere on some straight line, somewhere on the planet.

Yeah.

And so going back to the days of Captain Cook, they would take sites and get what was known as a noon site.

And that was when the sun was at its highest point.

And the benefit of a noon site was that that meant that the sun was either directly to the north or to the south of you, depending on where you were.

And so when you drew that line, it was in fact a line of latitude.

So that meant that you knew where you were in a north-south context.

Yes.

Well, it seems ridiculous now when we deal in centimetres with GPS, but back then one degree meant an error of one nautical mile, nearly 2000 metres.

So when you're bouncing up and down and you're trying to sight upon a very small star, for example, it's incredibly difficult and you're trying to

get the angle correctly.

And the other thing that you need to do is that you need to have the time exactly right.

So you're juggling a piece of paper and a pen and the time and the angle.