[HN Gopher] How to use a watch as a compass
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How to use a watch as a compass
Author : jamesgill
Score : 153 points
Date : 2022-10-19 18:23 UTC (4 hours ago)
(HTM) web link (www.citizenwatch-global.com)
(TXT) w3m dump (www.citizenwatch-global.com)
| frankus wrote:
| Don't forget to subtract an hour if you're on daylight saving
| time.
| tejtm wrote:
| and your offset within your time zone
| quickthrower2 wrote:
| cross reference with a reliable compass too!
| tmtvl wrote:
| Doesn't work quite as well with a digital watch.
| marktolson wrote:
| I hope this is a joke.
| madcaptenor wrote:
| 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...
| quickthrower2 wrote:
| Fun but probably useless as an actual compass for navigation with
| maps which requires higher accuracy.
| [deleted]
| praptak wrote:
| Daylight saving messes this up a bit.
| askvictor wrote:
| Probably not any more than big timezones do.
| ottoflux wrote:
| 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.
| throwaway4837 wrote:
| 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.
| rosywoozlechan wrote:
| Right, if you can see the sun and know the time of the day why
| do you need a watch for this.
| Terr_ wrote:
| 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.
| re wrote:
| It would be fascinating to see a visualization of how the
| accuracy of this method varies given parameters like latitude,
| time of day, time of year.
| quickthrower2 wrote:
| And local/national government politics (aka stuffing around
| with daylight savings and carving out new time zones)
| madcaptenor wrote:
| Don't tempt me, I have real work to do.
| nevster wrote:
| Don't forget to flip it if you're in Australia! Half-way between
| 12 and hour hand is North.
| kije wrote:
| 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!
| soperj wrote:
| You'd be pointing South no? Or is this for the southern
| hemisphere?
| kije wrote:
| 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.
| zmgsabst wrote:
| Doesn't N or S reverse at noon?
|
| 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.
| HillRat wrote:
| 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).
| mckeed wrote:
| 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.
| [deleted]
| ww520 wrote:
| Ah. This is the Boy Scout trick learned when was a kid.
| pwillia7 wrote:
| I'm more impressed with someone using it to determine the favored
| starting line for their yacht race. https://www.citizenwatch-
| global.com/support/exterior/yacht.h...
| Kon-Peki wrote:
| 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.
| xcambar wrote:
| If I know the time and see the sun or shadows, I approximate the
| direction by estimating the course of the sun.
|
| It always works significantly well, meaning I never need it on
| critical situations and the margin of error is bearable.
|
| But I'm mostly surprised not to see someone else comment the
| technique before. Is it not a known technique?
| uoaei wrote:
| 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.
| Nition wrote:
| 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.
| codeflo wrote:
| 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".
| dheera wrote:
| You'd also need a 24-hour watch, as the sun makes a full 360 in
| 24 hours, not 12 hours.
| fiddlerwoaroof wrote:
| This just means you go halfway between the hour hand and the
| 12 marker.
| system2 wrote:
| If I see the sun, why would I need a watch to tell me where south
| is?
| usrusr wrote:
| 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.
| certifiedloud wrote:
| only because you'd need to know what time it is to know where
| south is relative to the sun.
| chasd00 wrote:
| don't you only need to know if the sun is rising or setting?
| or basically if it's morning or not?
| dctoedt wrote:
| An old Boy Scout trick.
| b3morales wrote:
| I had a watch with a bezel like this as a kid, but over the years
| I'd forgotten how this technique worked. A nice refresher!
| politelemon wrote:
| 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
| mckeed wrote:
| 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.
| kqr wrote:
| No. Earth still makes a full rotation in 24 hours, at a fairly
| constant angular velocity.
|
| The only thing that changes during longer days is the height of
| the sun over the horizon, not its angle along the surface of
| the planet.
| TobTobXX wrote:
| 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.
| AdmiralAsshat wrote:
| Is that what the rotating dial on my watch is for?
| askvictor wrote:
| 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.
| tomjakubowski wrote:
| Also for measuring durations.
| Xylakant wrote:
| > Positioning the rotating bezel so that it points south, will
| then allow you to read other approximate compass directions.
| owlninja wrote:
| Likely more for this:
|
| https://www.citizenwatch-global.com/support/exterior/measure...
| est wrote:
| You don't need to remember the method, you can deduce it from two
| simple facts:
|
| 1. In a perfect world, 12 o' clock is where sun at its highest
| peak in the sky, 24 o' clock is where sun below the horizon at
| its lowest.
|
| 2. If your are in northern hemisphere, the sun's trajectory is
| slightly off to the south.
|
| Now try emulate the sun's rotation with your watch's hour hand.
| TheRealPomax wrote:
| The word "deduce" is doing _a lot of heavy lifting_ here.
| vesinisa wrote:
| This trick alone is why I think if daylight saving time is ever
| abandoned we should switch to permanent winter (~natural) time.
| gonzo wrote:
| 1959 edition of the Boy Scout Manual "Time for North"
|
| https://mediafiles.scoutshop.org/m2pdf/BePrepared_Vol_3_No_9...
| bigmattystyles wrote:
| 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.
| mordechai9000 wrote:
| 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."
| psychphysic wrote:
| This is a great trick and with practice you don't even need a
| watch, heck you don't even need an object to cast a shadow.
|
| 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!!
| chrisseaton wrote:
| > 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.
| CSSer wrote:
| Normally an upvote is enough but I just have to say that your
| enthusiasm about this made me smile so wide. This is great.
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