nova_robotics (Jun 12, 2021)
Nautical miles are one of the few "trade" units that makes some real common sense.
The generally accepted average* radius of the earth is 3959 miles = 3440 nautical miles.
The average circumference is 2*pi times this value = 21616 nm.
The circumference includes an angle of 360*60 = 21600 arcminutes.
So dividing we have 21616/21600 = 1.0008 nm/arcmin, an extremely convenient result for a navigator working with charts calibrated in angles.
* The earth is an oblate spheroid due to its rotation so the radius is not constant.
Marv's right [as if...lol] about nautical mile, though it's not historically clear how they arrived on that figure with combination of good mathematics and former state of the art instrumentation. But our degrees working in divisible 60's falls right in with all of it.
Side note. Ancient Greeks had no [known] practical use of navigation beyond coastal, sailing from landmark to landmark. But they proved quite accurately Earth was spherical, misshaped or not, and Equator within ~800 miles of actual. It wasn't until fuzzy theology aberration of science manipulated the truth, even support to flat earth nonsense. I digress.
Back on course, All Ahead 2/3rd.
In daily use a nautical mile is rounded to 6000 feet for the best reason of all. It's fastest possible mental calculation of speed and distance, awfully handy when the course of vessels will cross or be head-on, to avert collisions. So plot of voyage could utilize correct distance to figure arrivals, and divert to 6000 if need arise.
Quite similar to when you set alarm clock to wake, allowing morning routine and work commute, and expected arrival time.
At sea, known as 'DR' or Dead Reckoning. Prudent masters verify actual position with prediction AND previous coordinates, often at each half-hour. It shows headway [speed], drift [off course], set [off course by wind and/ or current]. Of three components [Time, Speed, Distance] any two arrive at the answer.
I saw this manifest last weekend, driving south out of Nebraska. We've all chimed in about systems of measurement; which includes something aside from accuracy, that of interpretation. In some ways, Time, Speed, Distance are subjective on their own, perhaps "we're hungry, they close at midnight." "Well, this jalopy only goes 55 mph." "Oh no, it's 60 miles away."
Q. Will you make it? ?...........
A. (what time is it?)
Even better, saw this, should have pulled over for a picture. Many of our highways have travel stops; catering to over-the-road truckers, road-trippers, traveling families on vacation, and single guys hauling machinery...
A sign for the next one said "41 miles; that's 287 dog miles."
Handy, as I was already channeling my inner dog.
Scientifically speaking, unsure 7:1 works on that guy. He's crazy about going along for rides; any chance he bolts through house door, he becomes a concrete statue until car door opens, no way getting him back indoors.
4 or 5 laps around the block will not trick him.
Last edited by Toolmaker51; Jun 8, 2021 at 05:32 PM. Reason: I redirect digression with anecdotes and levity
...we'll learn more by wandering than searching...
Had me a dog. Anytime I would rustle anywhere except to the kitchen or the bedroom, that dog was a statue by the door and facing outside. No ask. No refuse. 100* outside or 0*. If it was time, that dog was ready. Good dog, too. She wouldn't let anything near her car. I offered a ride to a hitchhiker without asking the dog. At the door to the pickup, the hitchhiker wisely declined the ride when he saw all the slobber on the passenger window. She tried to add toothmarks, but she couldn't get her mouth over the glass. Boy was she loud about it. hee-hee
My windows; nose prints out number drools 5:1. A bit oily, so removal a bit harder.
I put off cleanings [advantage of a 4-door] and complain kindheartedly.
Right now, sitting in my easy chair with laptop. He's on floor, head and neck draped over my booted instep.
I'll buy all the window cleaner and paper towels required.
...we'll learn more by wandering than searching...
This thread about the dogs is the first I saw this morning. Just got up. Silly dog knew it was time. I was planning to sleep in a little this morning. She knows the routine, get up, check emails, got for a walk, then get started working.
Right now she is laying beside me, between me and the door. After I write this, we will go for a walk. During the day she "hunts" around the property keeping it clear of anything she does not like around. Geese, crows, buzzards are chased from our air space. Hawks she does not bother. We have no ground hogs or skunks, etc. We do have a couple fox which she tries to catch, fun to watch that, but I do hope she does not catch one of those.
She also loves to ride, "lets got for a ride" or just the word "truck" brings her to attention and she is ready to do. One day, while working outside, she disappeared. I called and called, was getting mad as I had to get going. I had left the door open to the truck, she was in her spot, "smiling" like they do. I figure she was thinking, "stop whistling for me and lets get going." Now when I am working outside, I leave the doors open so she can rest in there when she is done hunting.
Right now she is starting to squirm, looking at me with that "lets get going" face. Funny how well they train us to do what they want!!
Toolmaker51 (Jun 9, 2021)
Back in the day when I was helping to target ICBMs, we would occasionally encounter data expressed in nautical miles and had to convert it so the latter figure is burned into my brain. It's low on my list of things I wish I could forget but it's still there.
For TLAR purposes, a nice round 6000 is good enough.
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