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Comment by codeflo | Hacker News Reader

From some of the comments, I’m not sure people fully get this. It’s basically doing a geometric construction of the sun’s path across the sky, using the distance between the hour hand and the 12 on the watch face as one of the input angles in the calculation. That’s quick (important because you have to repeat it while you’re marching) and easy to remember (also important because you might need it in a situation without access to Wikipedia). Under the assumption that the sun rises at 06:00 in the exact East and sets at 18:00 in the exact West, the construction is almost perfect. Of course, that’s never exactly true in real life, but still a lot more accurate than “well I know the sun is roughly South”.

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> That’s quick (important because you have to repeat it while you’re marching) and easy to remember (also important because you might need it in a situation without access to Wikipedia).

I was taught this as a child, which was very accessible, felt incredibly magical yet made total sense, and super empowering.

I grew up in an hilly area with lots of forest, where intuitively orienting yourself can be hard in itself, doubly so consistently over even a short walk.

However imperfect, this technique allows one to consistently and unambiguously orient themselves via an absolute measurement subject to an error margin but impervious to error accumulation, and, when lost, not end up exhausting themselves to death by walking in circles.

Knowing that (plus orienting myself with stars at night, and a couple of other safety+emergency tricks) is probably why my parents allowed me to roam around freely by myself without anything like a cell phone (at the time they were at best an oddity that you saw in Hollywood movies), even at a very young age!

Most parents these day would probably pass out at mere the idea of a lone 12yo taking on a hike by themselves in such a way. For me it resulted in the complete vanishing of the fear of being lost; instead exploring by "getting lost" became the most thrilling activity ever.

Australian checking in. for the second time this week I'm commenting that your US/Northern Hemisphere sun goes THE WRONG WAY for my internal navigation instincts...

The sun is currently about NNE as I write this.

Their moon is upside down too

And stars are wrong too ;)

Not just wrong, they are totally different stars. Good luck finding the Big Dipper down under!

Maybe because I've seen northern hemisphere sky for 40+ years, the southern hemisphere sky is much more interesting to me. Just seeing Large/Small Magellanic clouds and realizing those are the closest galaxies to the Milky Way. Seeing Alpha/Beta Centauri and knowing those are the closest stars to our Sol. Just kind of different cool

On the other hand, having a Pole Star is a great idea. It’s not _that_ hard to construct south out of the Southern Cross, but a star (close enough to) on the pole is smart…

  >Good luck finding the Big Dipper down under!

Good luck finding it in Britain. It's called "The Plough" here.

A rose by any other name is still a rose. Pretty sure a Brit said that.

Their sun too

I’m not from the US, and neither is the sun, of course. I do believe that the “clockwise” direction was established to match the direction of the shadow movement on a sundial in the Northern hemisphere. It’s not just maps, even clocks are Eurocentric. :)

However, the construction is easy to adapt to counterclockwise sun movement in the Southern hemisphere by flipping everything around: point the 12 (!) towards the sun and take half of the angle from the 12 to the hour hand. This angle points North.

At around noon, when the Sun reaches the zenith (at least of you are not in the polar regions), it would be South in the Northern Hemisphere and North in the Southern Hemisphere. At that point, east-west axis is easier to establish. Doing this other than noon is going to get more distortions, based upon time of year and latitude. It’ll probably be reasonably accurate if someone is in the equatorial belt.

The equinoxes are the times when that east-west is going to be east west.

Thinking about this, this is probably how the clock and the sextant lets people navigate on the open ocean during the age of sail.

You've got the ideas right, but a few technical corrections :) (unless I get them wrong as well!)

> At around noon, when the Sun reaches the zenith

The sun approaches zenith, but unless you're at specific places and times of year (under the tropics, at specific time of year for each latitude), it doesn't really reach zenith. At its peak, I believe the Sun is towards Earths orbital pole[1], which is offset from the geographic north/south pole, although those directions coincide at solstice.

> Doing this other than noon is going to get more distortions,

Indeed, the sun approximately describes a circle around the north/south celestial pole at 360 degrees per day, or 15 degrees per hour. Near the equator the circle tends to be larger and follow direct east-west discussed earlier (in particular at those times when it reaches zenith, that near equinox in tropical regions, i.e. less than Earth's inclination latitude). This can be accounted for if you know your latitude and day of year. (I'd love to dive into the math of this)

> Thinking about this, this is probably how the clock and the sextant lets people navigate on the open ocean during the age of sail.

Indeed, very fascinating to me :) If you take measurements very precisely, you can approximate both your bearing and latitude position very well. If you have an accurate clock you can also infer your longitude, i.e. a celestial based GPS!

I don’t think it is exactly zenith at exactly 12 noon, though now that you mentioned it, I remember that the apps I use shows it might shift as much as +/- 30 mins where I am at. Playing with the app (Sun Seeker), I can see what you mean by different places and times of the year as it relates to clock time and zenith.

On the note about the age of sail, I remember that accurate maritime clocks revolutionized and enabled sailing, and colonization. Though at the time, I was mystified by how the sextant and clock would get location.

Two of my hobbies are permaculture and astrology, so I spent a lot of time observing the path of the sun as it relates to my location on earth.

You'd also need a 24-hour watch, as the sun makes a full 360 in 24 hours, not 12 hours.

This just means you go halfway between the hour hand and the 12 marker.

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