NerdGuy Fridays #5: Knots and Lines

Knots of Latitude

I love my proofreader. We've been working together for years and she will chase the most obscure facts right down the rabbit hole with me. She's incredibly hard to stump. But she's learned to sometimes just put in a comment... "I couldn't find this...after 1/2 an hour of looking." I, of course, then send back how I came up with that obscure something and send her plunging right back into the rabbit hole. (No, that's not my evil smile.)
So, she tripped on a fact in my newest book, Miranda Chase #3 Condor. "Polyarny submarine base, three hundred kilometers north of the Arctic Circle." A seemingly simple statement, but a real pain to verify...unless you know how I came up with it.
Here's my explanation back to her:
Per Wikipedia, Russian Shipyard No. 10 (aka Ployarny, where the Red October departs in The Hunt for Red October) lies at a latitude of 69°12’ N versus the Arctic Circle at 66°33’ N, subtract the two to get 159 minutes apart (60 minutes per degree). A minute of latitude = a nautical mile. So 159 minutes = 159 nautical miles = 294 km. Wasn’t that obvious?
For lines of latitude (parallel to the equator) each degree is made of sixty minutes. Each minute is one nautical mile, roughly 6,076 feet.
Fun Game: How far are you from the equator? Find your latitude, then follow this example. The rather curious big red rock in the middle of the Australian Outback (Uluru or Ayer's Rock) is at 25°20' S. (25*60)+20 = 1,520 nautical miles from the equator. (1,726 statute miles or 2,815 km).
Some trick the other way around: Uluru is 64°40' from the South Pole. (64*60)+40 = 3,880 nautical miles.
By the way, this only works when traveling north or south. Lines of longitude don't work that way at all. They're a mile (nautical) apart at the equator, but touching just as they reach the poles.  However, if you're looking at a map marked with latitude (like a good hiking map), a minute along the vertical can be used to then measure a mile at any angle on the rest of the map. Just remember it's a pretty long mile if you're used to hiking in statute (5,280') miles rather than nautical ones (6,076').

The Arctic Knot

The Arctic Circle lies at 66°33'48.0" N (read as 66 degrees 33 minutes 48.0 seconds [60 seconds per minute, just like time). Except that's only where it lies at present.
The Arctic Circle isn't some specific distance from the Equator. Rather it is the line above which the sun never sets on the Summer Solstice and never rises on the Winter Solstice. Same effect just upside down at the Antarctic Circle. (That's a tease to Holly Harper, my structural specialist in the Miranda Chase thrillers. She from Oz (Australia), and they hate the phrase "Down Under." Hi, Holly.)
So, as the axis of the Earth tilts its way through a slow (41,000 year slow) precession (no, the North Star is not always the North Star which I'll nerd out on some other time), the Earth changes its angle to the sun. As it does, the Arctic (and Antarctic) Circles move. Right now, it's moving north. So, to be more precise to my proofreader and any far future readers, Polyarny is becoming 15m closer to the Arctic Circle every year. In just 66.67 years (at current rate of shift), it will be another kilometer closer to the Arctic Circle.

Bonus knots

Bonus Fun Fact: marine and air speed is almost entirely in knots (nautical miles). Why the holdover? One, probably because the US is the final stick-in-the-mud country in the world to still use the English measurement system. Second, to change everything at once, worldwide, so that someone isn't suddenly traveling in miles vs. knots vs. kilometers and colliding with each other, is an unimaginable task!
In fact, air traffic flight levels globally are still in 1,000s of feet for that same reason. Flight Level 250 = 25,000 feet everywhere in the world.
Bonus Thought: Ever wonder where the phrase "A mile a minute" comes from. Well, every resource I can find points to the 19th-century's belief that to travel 60mph was lethal to body and soul (the first we've proven many times on our highways and I wouldn't dismiss the latter too lightly). But it's a really useful measure that goes back to the 15th century.