NavList:

"Why do we still use knots? Pretty obscure- makes almost no sense at all in modern times."
"Ooooh! Don't say that!"

Of course the creators of the metric system back in post-1789 France tried their best to get rid of minutes of arc and hence knots. It would have worked, but practical people objected. Navigators? I don't know of any, but I'm sure some perhaps whispered their concerns ("perhaps whispered" so as to avoid the fate of that H₂O chemist Lavoisier). But apparently it was the astronomers who objected. The "rationalized" metric system would have kept the essence of the nautical mile but replaced it with both a new physical distance and a new angular measure. The new physical distance, the kilometer, survived. The angles, with 100 "grads" in a right angle? No way, except in 1970s-designed electronic calculators for some strange reason. Too much long-established astronomy built around the sexagesimal degree system.

In Tyson's muddled, annoying video (which I only skimmed, so maybe I missed it), he never said that there is a simple, nearly perfect integer relationship between kilometers and nautical miles. It exists because the same principle for defining nautical miles was used to define kilometers. The nautical mile was defined so that there are 90·60 or 5400 from equator to pole while the kilometer was originally defined so that there are 100·100 or 10,000 from equator to pole. There are then 100km in 54 nautical miles almost exactly. Only small modern re-definitions have --very slightly-- spoiled that integer match-up. The creators of the metric system intentionally borrowed the principle of the nautical mile, switching to decimal counting and junking the sexagesimal. Modern navigation, celestial and otherwise would be significantly simpler at the basic arithmetic level, if those revolutionary zealots had succeeded! Incidentally, although it crosses the line and mixes the sexy with the deci, it is also useful to realize that 100km is almost exactly 0.9° along any great circle on the Earth.

The most useful, though, is the basic 54:100 ratio. What's 108 knots? Easy: 200 kph. What's 133 knots? Easy: you ask your internet-connected device, and even without a drop of A.I., it has replied with a perfect answer for two decades (more or less). But if you need to get a quick estimate off the top of your head or "on the back of an envelope", that 54:100 ratio is always available and easy to apply.

Why don't we get rid of nautical miles and minutes of arc in celestial navigation? We can. Easily. The job could be done in under a year, and in my Modern Celestial workshops (next run at Mystic Seaport in late January and online in early February, we do everything with decimal degrees --still degrees, not "grads" but we get most of the arithmetic benefit). Why won't that be adopted more widely? There are many reasons both practical and cultural.

Are we stuck with nautical miles then? Nope. Have a look through NASA mission logs, and you'll find nautical miles in the early era, but replaced by SI units relatively recently. There were some complaints, no doubt, not even whispered since guillotining is out-of-fashion, but in the end consistent SI units have caused no lasting problems.

Who's next? Can aviation get over the nautical mile and knots addiction or is the inertia of the "installed base" simply overwhelming? And what about meteorology? Winds are often listed in both knots and mph (US "statute" miles per hour). When it comes to hurricane force winds, it hardly seems to matter to most people. Is that good, bad, or just "one of those things"?!

And finally a little history to contemplate: when did the expression knots per hour finally disappear in nautical usage? It wasn't always the case that a "knot" was counted exclusively as a speed unit since, after all, navigators with log lines were counting off actual knots in a rope, as the lined paid out. Today, for us raised on modern units, the phrase knots per hour sounds like a blatant mistake (since we know they don't mean acceleration by context). No doubt someone can point to books specifying formal definitions, but when did real practical navigators finally "get the idea"?

Back at the top, I described Tyson's video as "muddled, annoying". He has gotten much worse over the years (he's approaching 70... certainly not old old but it's ths stratosphere in science). He used to focus on interviews and conversations, but when he tries to teach, turning to basic exposition, like in this video, he's all over the map. His prime days are behind him. The Twitter to X upheaval did great damage to his favorite social media platform --he was a huge Twitter user from the early days. And well before the Twitter/Musk/X insanity, he was very nearly ruined by fallout from his questionable behavior with women, especially employees. Although he was professionally "cleared", there is no court that heard his case except the court of public opinion, which either found him probably guilty or just shrugged it off.

Frank Reed