That works the best close to noon, but I don’t think that works so well at around dawn or dusk.
Latitude also matters. The closer it is to the arctic or antarctic circle, the iffier that gets.
This isn’t a trick so much as just how the sun and the earth defines the plane of the ecliptic and how we experience it because of Earth’s rotation.
There are some interesting things that can be done with starlight navigation. The Polynesans, for example, might navigate by latitude based on how far up Sirius is in the sky, or using the little dipper (and Polaris) in the Northern Hemisphere as a clock.
Starlight navigation is incredible. I was in the marines with a helicopter pilot who had a second set of wings on his uniform, an odd pair I'd never seen. Turns out he was a starlight navigator on C-130s before becoming an officer and getting his pilot's wings. He used to wear the starlight navigator ABOVE the pilot wings, which I always thought was incredible. The training and skills you need to get this set of wings is quite an undertaking.
I can navigate with a map and compass, but you're using terrain to help you locate yourself on the map. Being able to do it in the expanse of the ocean or the air, with only the stars is pretty amazing.
The concept of celestial navigation is actually pretty simple. Actually doing it requires physical skill.
The general idea is this. Take for example the star Altair, at any given instant it is directly above exactly one spot on Earth. If you were at that spot and measured it's elevation above the horizon, it would be 90 degrees. That point is called the "Geographic Position (GP)". So, if you were at some unknown location and measured Altair to be 45 degrees, you would know you were 45 degrees from Altair's GP, and all of the points satisfying that can be plotted as a circle on a map. Repeat that for another star and you end up with two circles that intersects at two points. You could repeat with a third star, but in practice you have a rough idea of where you should be, and you choose stars that produce a large enough circle that you can disregard one of the two points. And taking that "in practice" one step further, the diameters of the circles are so large, you really just need to draw part of the circle as a straight line, and that lets you plot in a small enough area that map distortions are of no significance (unless your very close to the poles). There's a standard form called a "VP-OS" which makes the process a lot easier. A video showing how to do it is [1].
To determine the GP of a star (or planet) you need an ephemeris of some sort, there's software to do it, but a copy of the Nautical Almanac provides enough information to make the process simple enough to do with paper and pencil.
Actually measuring the elevation of a star on a moving, bobbing ship is where the real skill comes in. At the equator, being off by one degree means your result will be off by about 60 miles. Skilled navigators can fix their position within a few hundred feet!
Leave it to hacker news comments to summarize something I thought was black magic into paragraph that I completely understand. Not sure I could replicate it but it makes sense to me now.
So, this has been around a lot longer than we had accurate star charts that actually understood the motion of planets and stars, right? Do you have any summary of how these charts that describe where a certain star is above on the earth on a specific day came from before we understood the motions of the stars?
I'm not too familiar with the ancient history of it, but it requires an accurate clock. There's a good book called "Longitude" that goes over the development of the clock that could be used at sea. But, before then, it was well known that you could measure the altitude of Polaris to get your latitude, so ships would sail to the latitude they wanted, then turn East or West.
We've had accurate star charts for a long time, Hipparcus had made accurate enough measurements to detect the Earth's slow 26,000 year wobble called precession. The key piece missing for navigation was a clock.
I assume that doing this technique with a computer and a camera could achieve really good accuracy - you really just need a zoomed image showing the horizon and some stars in a few directions, and by averaging across hundreds of stars you ought to be able to achieve perhaps 1/100th of a pixel of precision, which works out to 1.8 meters of position accuracy. Modern tech can see stars even in daylight too.
I wonder why that technique isn't used instead of GPS - back in the 70's before GPS was deployed, it surely must have been an attractive option.
Even today, in warzones with GPS blocked, it seems like a good option.
Uncertainty in atmospheric refraction limits exactly how accurate you can get. Celestial Navigation books say it's better to make several measurements of the same star than to measure a bunch of different ones.
From what I understand, some land surveyors often still use a sun sighting to determine true North.
GPS has the advantage of working when it's cloudy, or when the sky is blocked by trees or buildings. And a GPS receiver is pretty cheap, durable, compact, and foolproof compared to a telescope and camera system which will have to be recalibrated regularly.
On land, it can be hard to very accurately measure the horizon (mountains etc).
However you can use a similar technique by using a weight on a string to make a perfectly vertical line, and seeing the alignment between stars and that.
Something I only learned recently: Boeing 747's had a sextant port, for use in navigation. This is only one of several aircraft variants (including military aircraft) which used sextant navigation.
They do, you may also find this [1] interesting, it doesn't cover the starlight navigation system but the 19,000 piece Advanced Inertial Reference Sphere (AIRS)
Why does it work worse in higher latitudes and closer to dawn and dusk?
The shadow of the tip of the stick will always move in a straight line from east to west right?
At high latitudes I could imagine the shadow gets so long that finding the tip might become hard.
Around dawn and dusk, what is the problem? Does the shadow become too faint? Does the shadow move to slow to give a big difference in position?
At dawn and dusk, aka twilight, the sun is below the horizon. So you only get indirect illumination. Contrast is terrible, and shadows will be diffuse. The direction should still be mostly right, but you will be hard pressed to define the end of the shadow.
The position of the sun can be a bit weird depending on the season the further away from the equator you are. Especially in the periods where the sun never rises above the horizon. Other than that I don't know exactly what problems you might have. The midnight sun perhaps flips the direction?
Oh boy, I got sucked into those shorts real hard. How the hack (heck) does he guess the card those people on the street seemingly all by themselves picked?
It’s a rabbit hole but you can find some of the tricks online - you either do slight of hand, control the card picked (a force), or you control the card once in the deck.
Combining them and being really good at it is what makes it “what”!
The shadow is always going to be opposite of the sun, so it does not provide any extra info which the sun doesn't already give you.
In order to estimate the current time ("it's about 5 o'clock") using the position of the sun/a shadow - you need to know the cardinal directions. So, only if you already know where north is, you can tell the time from the shadow.
In order to estimate the cardinal directions from the position of the sun/a shadow - you need to know what time it is. So only if you know the time, you can tell where north is from the sun/shadow. And to know the time you need a watch or something similar?
But if you can deduce both time AND cardinal directions just using the sun/shadow and no other information... yeah, I have to agree, that seems like witchcraft!
> In order to estimate the current time ("it's about 5 o'clock") using the position of the sun/a shadow - you need to know the cardinal directions
On this planet the sun is always moving from East to West. And assuming you suddenly didn't wake up on the other side of the planet you know if you are in Northern or Southern hemisphere.
So if you are in Northern one, then shadows always point in the North direction, the difference between marks on the ground show you the sun direction (E-W).
More so, in the morning shadows point to NW, in the evening to NE, so you can have a vague estimate even without waiting.
> And to know the time you need a watch or something similar?
You don't need the time per se, you need to know what sufficient time passed, it's just hard to make a precise line with a sticks. But if you have something long and thin then you can make a line in a couple of minutes.
Just take a sheet of paper, anything sticky (even a pencil, just make it stay vertical), mark the shadow, browse Reddi^W HN for a couple of minutes, mark the new shadow, make a line.
We just don't notice it, but Sun is hurling through the skies with astonishing speed.
PS I can guess the current time with ~1-1.5h accuracy just looking through the window to see how the buildings are lit by the sun. Works only from my windows, of course.
The shadow measures not just the horizontal angle change of the sun, but also the vertical angle change of the sun.
A very common way to measure time is to reference the horizontal angle change w.r.t. noon.
In that case you need two moments where you measure the horizontal angle.
Where, for the first moment, you need to measure two vertical angles (probably more) and deduce that the sun has reached its highest point.
In this witchcraft, you still measure two vertical angles and two horizontal angles. You just split up when you take the vertical angles.
It's because the actual true statement is that the sun is in the East at 6 o'clock in the morning and in the West at 6 o'clock in the evening, and of course, if the sun rises at 3 or 9 (and perhaps you've got a timezone that's more than half an hour off of 'local sun time' and one more hour shift caused by daylights savings time) then it makes quite a difference.
But if you would have an analog watch with a 24-hour dial tuned to your local sun time, then you should be able to effectively treat it as a compass everywhere, also way up north.
> The sun is over there, a shadow would be that way, it's about 5 o'clock. That must be north!
That works for example if you have a path and you're trying to find out which way goes north and which south, but a watch can give you an actual quantifiable bearing that is actionable if you have no other ground orientation.
Or, if you’re in the Pacific Northwest and mistake the diffuse daylight for direct sunshine, you’ve probably started tracking crow movements by accident.
Isn't this incorrect? If it's summer, south of the Tropic of Cancer, the stick should be North of the line. It's the Tropic of Cancer where the sun is overhead, not at the equator. Or did I understand basic astrophysics wrong.
Similarly, in the winters, I'd imagine North of the Tropic of Capricorn would play the role of the Tropic of Cancer.
I have a wonderful book called the “Rudge Book of the Road” from the 1920s that’s full of stuff like this.
It was written as a companion for Rudge-Whitworth motorcycles and tells you how to determine direction of travel by looking at trees among other things.
Exactly. It depends on where you are and your concept of time.
In my long distance cycle touring days in places I had not been before, in open terrain, I knew what time it was and where north was just by where the glowy thing was in the sky. I had no need for a compass or watch, I was used to the movement of the glowy thing and it never moved unpredictably on a day to day basis. For a second opinion I could consult the current status of my sunburn and what hurt the most. For a third opinion I found surrounding flora was easy enough to read.
At night, under clear skies, it was the same story, the heavens always moved predictably to me, my in built 'star nav' worked great, I never overshot my destination or ended up going in the wrong direction.
This is all well and good, however, this innate ability can easily be defeated in a city. I am not sure maps helped, over reliance on such 'technology' rather than intuition has led me to head off in completely the wrong direction, often with two or three corrections needed.
I have a Rudge bicycle from the 1990's, a rebranded Raleigh import, notable for being an early foldable mountain bike.
Speaking of antiques, remember Scribd? There is your "Rudge Book Of The Road" there to download. Auction sites have the original for sale, 1927 vintage possible for a small fee.
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”.
> 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...
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.
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…
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.
I love this trick. You can also do this using your hands if you know roughly what time it is.
For example, if it's sunny out, place your arm in your shadow, parallel to the ground. Keep it there. This arm represents the current time (say, 10 O'clock).
Look at your shadow and point your other arm out, parallel to the ground, and adjust it until the arm's shadow points at "12 O'clock" relative to your first arm (in your shadow).
Clap your hands together, and you're pointing north!
Imagine (for simplicity) that we have 6a to 6p with solar noon at 12p.
Then if I put my right arm in my shadow at 6am and my other arm 180 degrees from it, then I’ll be facing South. If I do the same thing at 11 am, I form a big wedge with my right arm on the NW side, again facing South.
But at noon that changes: the sun is directly South from me, so my right arm is North and my other arm is in the same spot, so I turn around to face North.
From there, my right arm is on the NE side, and my left arm makes a widening wedge as I face North — until at 6pm, I’m standing with my right arm facing East and my left arm opposite it, facing North.
It doesn't work at 6:00 unless you know which way to face. At 11am you should have a small wedge, and your left arm should be in the shadow, in order to not point both arms straight behind you. At 1pm your right arm will be in the shadow for the same reason, so you're still facing north.
At sunrise or sunset, it's pretty obvious which way east or west is. At least to a first approximation.
For a second approximation you'll want to interpolate between the equinox and solstice and use that to approximate an allowance for the ~24 degree tilt of earths rotation axis.
That second approximation error is there for all times that are not midday, but reduce to zero as you approach midday.
A third approximation might be to allow to the offset between your local timezone and solar midday. Where I am (Sydney) we are fairly close to the middle of the +10 and +11 timezone boundaries, so solar noon is within a few minutes of timezones noon. Perth on the other hand is way out to the west of it's timezone, so solar noon there is almost 25 minutes off from timezone noon. So "watch north" in Perth will be about 7.5 degrees off "true north".
Yes -- the article doesn't explain this, but in the morning you use the clockwise side of the hour hand to find south, and in the afternoon the counter-clockwise side (IIRC).
Compare it to the parent article and you'll see what I mean. If you are the center of the watch and you put your hand in your shadow, it will face the direction opposite of the hour hand in the article. If you adjust your other hand to face 12 O'clock relative to that hand, it would be at 6 O'clock if you're going by the article. So the direction is flipped. When you clap your hands together, you'll be facing North instead of South.
Southern Hemisphere version: Instead of pointing the hour hand at the sun, point the twelve o'clock at the sun. North is approximately half way between the hour hand and the 12.
Meh. If you know the trick exists, you can derive it from first principles, which for some people (me included) is a much easier "trick" than accurately remembering the exact steps/process for something like this.
Maybe there's a important semantic difference between derive and deduce? But I totally agree with the grandparent poster.
Very impressive reaction from the guy in the video, but I don't think he's using this to tell the heading. It looks like he also has a compass on his watch band as you can see at 1:03.
And the angle they point up is (very roughly) the inverse of the latitude. A dish near the equator (0 degrees latitude) points 90 degrees up, a dish near the pole (~80 degrees latitude) points 0 degrees up (tangent line), a dish halfway between there and the equator points about 45 degrees up, and so forth.
That's true for dishes where the feed horn/antenna is inline with the dish axis. A lot of smaller satellite dishes nowadays use off-axis feeds. But you can do a bit of mental geometry to adjust.
Assuming they're communicating with a geostationary sat of course - and the vast majority of sats these days just aren't (Starlink constellation being an obvious example of thousands).
Even the quote from the wikipedia article [1] is dubious:
> Weather satellites are also placed in this orbit for real-time monitoring and data collection
as many weather and climate satellites are on near earth polar precession orbits to rapidly scan (obit time between one and two hours) a full circle about the planet for a full picture.
That's a good point. Still, the use of a fixed parabolic reflector dish involves aiming it at something, which would ordinarily be a point in the sky where there is a particular satellite, hence a geostationary orbit.
For other applications where the satellite move around, I wouldn't expect the antenna to be a parabolic dish. It looks like Starlink's isn't, although their original one is more curved than I'd have expected.
Maybe I'll modify this advice in the future and say "the curved satellite dishes that aim at a point in the sky are pointing south".
Of course what you describe is the main way people navigate by the sun, when the margin of error is bearable. In more extreme situations where precision is needed, decimating the margin of error is pretty important, especially when used in conjunction with a map or known landmarks.
Isn't this just using the sun as a compass? You could easily just look at the position of the sun knowing what time it is, or use your hand and make a sun-dial. I believe the watch is only there to tell us the time and cross reference that with the sun's position.
Yeah, the strategy only really involves (A) knowing the current time and (B) a protractor or a good sense of angles.
Or in word-algorithm form:
1. When the sun rises that's usually at 6AM in the East, at 12AM noon it's usually towards the South, and when it sets that's usually 6PM in the west. (Valid for northern hemisphere only.)
2. Use the current time to linearly interpolate between those three values.
3. Once you know the heading of the sun, you can figure out which way is north.
Essentially this means approximating the bearing of the sun X hours after midnight the sun as 15X degrees. This works better the closer to the poles you are and the closer to the winter solstice it is - see for example https://possiblywrong.wordpress.com/2012/01/25/using-a-watch...
I learned this from Gallipoli (1981 Peter Weir movie about WW1). In the movie they get totally screwed by this trick when it turns out it’s overcast.
Tangent, that movie is great, the synthesizer music is odd but to me it works and the whole movie is beautiful.
My parents showed me that movie when I was maybe 9 or 10 and getting that boyish fascination with war (amongst a few other war movies like Das Boot). I didn’t understand the colonial subtext of the movie, which made it that much more impactful. It has absolutely stuck with me, both in terms of the absolute insanity of warfare, but also just how life in general can be a complete tragedy.
I've been to-and-fro across much of North America for much of my life. I have never encountered a situation where it was especially challenging to orient to the cardinal directions in a few minutes using a few basic clues; how trees and plants orient, satellite dishes, how houses are oriented, the stars, the time of year and the subsequent location of the sun, how streets are planned, named & numbered. Even a cursory glance at a map can help you identify major terrain features that can help you orient.
Have never had to resort to these methods of using a watch or a magnetized needle, because waking up in in the middle of a mysterious jungle is a pretty rare event ;)
>I've been to-and-fro across much of North America for much of my life. I have never encountered a situation where it was especially challenging to orient to the cardinal directions...
This is one thing I always find quite odd on American TV / Films.
People [eg. police pursuing someone] will inevtiably say something like "He's turned north onto 21st St." or "He's heading east on 12th street". I always wonder how they know the compass direction. I don't think many people in Britain would express directions like this, using compass points, or even know which direction was which.
Do US streets have the cardinal directions on the roadsigns, or are you all issued with built-in compasses at birth?
> Do US streets have the cardinal directions on the roadsigns, or are you all issued with built-in compasses at birth?
A lot of cities have somewhat gridlike street patterns, and those are often roughly oriented to the cardinal directions, so in those places, people will use them that way. (This is especially true in cities that are relatively flat and were mostly settled by colonists after the mid-19th century. Look at a map of Pierre, SD, Denver, CO, or Wichita, KS.)
Even when it's not north-south, people will still do this. In Manhattan, for example, the streets are actually offset by 29°, but people will still say "east" or "west" to mean "towards the Hudson/East River", respectively.
But also, the dialogue in cop dramas is always going to be forced and artificial, so I wouldn't read too much into that anyway.
It's a shame really that most watches are 12 hour time. With a 24 hour clock (with noon at the top/midnight at the bottom) the hour hand tracks the Sun and North is at 12. And it's obvious enough that you don't even need to remember how it works.
In the Southern Hemisphere you need a clock that goes anti-clockwise (or you can mentally flip it).
This is a very cool use for a watch. You can use any watch, but some watches, like the Seiko Alpinist, even have a rotating bezel with the compass points. This makes it a lot easier to find the other directions. One thing the article forgot to mention, is that the trick works only for standard time. If you are on daylight savings time, the direction will be off.
Depends: are you the kind of person who considers it a good idea to be aware of uncertainty? You'll be perfectly happy with "I'm on the northern hemisphere, it's afternoon, so south must be somewhere left of the sun".
But if you are the kind of person who like to lose themselves in point-something percentage point deltas in small (or unknown) sample size market research, go on, pat yourself on the shoulder for building that makeshift shadow observatory, it will make you happy even if you don't really know where exactly you are relative to the center and natural bounds of you time zone.
This is a great trick, but they leave out the rest. At least give people a link to learn how to use a compass and map together. I suppose walking in a general direction is good, but learning how to read a map, orient, triangulate your position, take a bearing, then travel that direction is a super valuable skill if you're ever in a situation that you actually need to know how to use your watch as a compass.
It's nice that the explanation starts with this disclaimer:
> Keep in mind that these determinations are approximate as there is some discrepancy at different latitudes and in different seasons.
But it doesn't explain that this only works on the northern hemisphere, and in summer only if you're well above the tropics. Near the equator, this isn't going to work at all, and on the southern hemisphere, everything needs to be reversed.
It's a cool trick, but I think just understanding the relationship between the earth and the sun is easier and more universally applicable.
This is a good way to get a general idea, but unless your local solar noon happens to coincide with noon on your watch, it's going to be off. For instance, solar noon at my current location is around 2:00 pm.
As long as the sun is out, it's a good way to stay oriented and keep to a general heading. It works well when combined with local features and topography. So you can say something like "I'll keep heading more or less south until I see the river, then I know I can follow it upstream to the bridge and intersect the road back to my car."
Wouldn't this be messed up on longer days, like in summer when the sun rises at about 4 AM and sets at 9PM? Or similarly, winter when the days are really short
No, fo the same reasons sun dials still work: The sun rises at a slightly different point on the horizon. The trick even works north of the polar circle where there may be 24h days, as the sun is always in another direction.
The sun moves around, whether it is above or below the horizon, so the trick works regardless of length of time the sun happens to be above the horizon.
Yes, at 6:00 you have to know which side to put north and south, and from 6pm-6am it will be North instead of South between the hour hand and 12. If you know the sun rises in the east, though, you can account for that and the trick can still be helpful.
Something I was just wondering about recently: If the earth's magnetic field (and other similar "passive" global effects) can be sensed enough to move a compass needle, can it be used to power low-energy devices?
Like could we ever have always-on displays (like 0.00001 FPS, 10x10 pixels or whatever) or whatnot that are powered by the planetary magnetic field?
Sadly it's not enough to have a force; it needs to produce a motion (to perform work). Think of the analogy with a ball feeling gravity at the top of a hill: it has the potential to release energy but it remains unrealised until it starts rolling downhill. Once in motion energy can generated, say by coupling it to a dynamo, but once the ball is at rest at the bottom then even though it still feels gravitational attraction there is no power output.
You can do this (crudely but effective enough) with a any watch if you take a second to make a simple sundial. Rotate it with the stick (or whatever) until the shadow reflects the actual time and you’re pointing North (in the Northern hemisphere). It helps to be familiar with the angle range of how time is broken up in the day on a sundial but it works.
There are usually going to be too many other factors at play to use this to your advantage at the start, but occasionally you’ll see someone start a race on a completely different tack than the rest of the field and go on to finish far ahead of everyone else.
Edit - to be clear, almost everyone figures out and starts on the favored tack - you don’t really need a sailing watch to do this. In races with heats or starting groups, you have to do this 10-15 minutes before your start, because once the starting sequences begin you don’t get near the start line until it’s your groups turn. So the advantage comes from recognizing and adjusting to any wind shifts that may have happened in the few minutes before your race.
It's a different application, and there are no trees or terrain on the ocean. The sunstone reveals the position of the Sun when the sky is overcast, and from the position of the Sun one can not only determine direction, but also time of day. If there is a way to use a compass to tell the time of day and the position of the Sun when the sky is overcast, I'd love to learn it.
As I understand, a sextant can be used with a nautical chart, a compass and an accurate time keeper to find position, as long as a horizon can be found and you have an idea of your latitude. While a cool viking discovery, they aren’t really practically useful.
> Well the OP is about using a watch to find North.
False, or at the very least this description is incomplete. OP concerns using a watch and, critically, the position of the Sun to determine cardinal directions. If the Sun can't be located, the exercise is pointless.
> As I understand, a sextant can be used with a nautical chart, a compass and an accurate time keeper to find position,
A sextant is used to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation. If the sky is overcast, a sextant is useless. Earth's skies are cloudy, and at any time 67% of the Earth's surface is typically covered by clouds, and this is especially true over the oceans where less than 10% is entirely clear of clouds.[1] But in the case of having a sextant, nautical chart and a time keeper, under overcast skys, the sunstone can replace the compass and permit the function of the sextant, and one would still be able to find position under overcast skies that would be impossible without the sunstone and with a compass.
> as long as a horizon can be found
This is not a given as weather rarely cooperates. Fog is a common occurrence on the ocean, and it will conceal the horizon.
> and you have an idea of your latitude.
I'm pretty sure those 4 items are all that is necessary to determine latitude.
> While a cool viking discovery, they aren’t really practically useful.
As explained above, on the ocean, cloud cover ordinarily obstructs the position of the Sun. So a sunstone is practical under common conditions on the ocean of skies obscured by cloud cover.
This reminds me of my father showing me as a kid: if I hold my watch exactly in this position in relation to the sun, and look at it from this exact angle, I can tell exactly what time it is.
For SCUBA diving, it is to tell you how long you've been underwater for, so you can determine (among other things) your nitrogen saturation. I'm not sure if the original design was specifically for that purpose, but every (dial-based) diving watch has such a ring.
>I'm not sure if the original design was specifically for that
The rotating dial (I'd rather call it bezel) literally has NSEW and degrees on it, it can't be original for counting time in diving.. Or maybe you're talking about different types of dial here?
The sun is over there, a shadow would be that way, it's about 5 o'clock. That must be north!
What I've always thought of as witchcraft is this.
Jab a stick in the ground, mark the end of the shadow. Come back some time later say 15-30mins. Mark the new end of the shadow.
Draw a line between marks and that is an east-west line!
In the Northern hemisphere the stick is south of that line, in the southern hemisphere it's North!
What!!