Sextants, navigation and such

My main interest is to talk about use of such archaic (?) tools. Despite my shallow understanding and no experience, we might smoke out some skilled persons here.

First understand that latitude is how far you are from equator, that being circle of earth’s daily rotation. Longitude is how far you are ‘around’ the sphere away from arbitrary zero line perpendicular to latitude. After not much dispute, zero line was set to Greenwich UK. Longitude is also time, see below.

These things mostly matter(ed) for ships at sea. On land, just walk into a bar and ask where you are. At least one person might know.

At sea, lacking bars, determinations of location were DIY. People have been setting out in boats since we don’t know, and lacking maps and location-knowing, many found themselves wherever, or as fish food, or other brave (sorta pointless) end games. Knowing locations better, at sea, was at least an economic proposition.

Duff mariners apparently toodled about for thousands of years, collectively. About AD 1730, with global maps having become useful, folks got cranking on determination of latitude. Knowledge of where ‘things’ ought to be in sky (ephemeris; it is a book), vs. one’s location and a vague knowledge of time, those together provide brave sailors their latitudes. Lacking only a gadget to determine astro-objects’ angles above horizon.

We retreat to about 200 BC to consider astrolabe. High tech then, I guess, the version 1 latitude finder. Not very good, and supported by a not-very-good ephemeris. But, y’know, sailors gotta sail. They became fish food, as often as not.

AD 1730 thing was sextant, a nice machine. Nowadays one can buy a crap reproduction of this seminal navigational version 2 device for ~$50. Sextant allows one to find a very accurate angle of sky-things to horizon. With training and ephemeris book in hand, nail your latitude even with an inaccurate clock.

But of course, sailors wanted longitude as well, which was totally tied to more accurate clocks. Several books I don’t link examined their development. I am, transparently, goading some readers here to engage this topic.

Looking at the sky with gadgets supported by accurate clocks to know where one is had about a 2-century run. Current and future technologies will never again have 2-century runs. Earth’s oceans are now plied by vessels knowing their positions at 10-meter scales or better. At very least this is version 3 of knowing ‘where am I?’.

 

John Harrison@3. Oh yes.