Finding north with a wristwatch, having trouble.

[user24]

Hey guys,

I've been trying to practice finding north using an analogue watch.

It's now 10PM (9PM UTC) and I'm pointing the hour hand at the sunset. Bisecting the angle between the hour and 12 gives me a line that runs between 10:30 and 3:30.

Everything I've read tells me that north will be at the end of the line that's furthest from 12. The only problem is that that's not right. The north/south line is spot on, but north is actually at the 10.30 end not the 3.30 end.

What am I doing wrong?

 

[ScoobySnacks]

First point, 10:30 is not opposite 3:30 on a clock dial. Run a line through 3:30 to the centre, carry it on the other side and you go through the other side at 9:30. If it's at 10:30 then the other side will be 4:30. For the line to pass through the middle there has to be 6 hours between the two times.

I've managed to confuse myself now with the orientation.

The North point is the point bisecting the arc between the hour hand and the 12, in a clockwise direction. Start at the hour hand and count round half way to the 12 o'clock. So if the time is 2100 (9pm) then your N point is at 10:30, as you've found.

The South point is the opposite point, obviously, so start at the 12 o'clock and work clockwise half way to the hour hand and you will find south.

Out of interest, the same works in the southern hemisphere, but you have to point the 12 at the sun.

Hope that kind of makes sense?

 

[user24]

First point, 10:30 is not opposite 3:30 on a clock dial. Run a line through 3:30 to the centre, carry it on the other side and you go through the other side at 9:30. If it's at 10:30 then the other side will be 4:30. For the line to pass through the middle there has to be 6 hours between the two times.

Whoops, I meant 4.30

Now, the North point is always half way between the 12 and the hour hand, in a clockwise direction, so starting from the midday point, go half way to the hour hand and that's your North point.

That would still put north at 4.30 not 10.30 though. I must be doing something stupid but I just can't work this out. I'll revisit it tomorrow when I can get a better look at where the sun is, I might have mis-sighted it.

 

[ScoobySnacks]

Sorry user, I got myself muddled up, I've edited the post so it should make sense now!

 

[user24]

That makes a lot more sense! So clockwise from the hour, half way to 12 is north. That's spot on

Cheers mate!

 

[user24]

Hang on, this can't be right. That means if you check it at 9PM and again at 9AM, north will be in a different place.

You must have to adjust the method based on whether it's morning or afternoon?

I mean obviously if it's morning you can say "well, the sun's in the east" and work out north from there, but it seems like there's a lot of incorrect info on the interwebs about the technique. Lots of sites just say "half way between hour and 12 is north".

 

[Golb]

Don't forget about the light saving time. You are living in a

UTC/GMT +1 hour time zone, thus you need to make a bisection between 1 and the hour, pointing the hourhand to the sun. This bisection is pointing south. The opposite site is north (obvious )

If you are living (like me) in an UTC/GMT +2 hour time you need to make the bisection between 2 and the hour hand. At 2 o'clock (1 o'clock for you) the sun will be exactly in the south. ​

 

[Golb]

The sun will be in a different place, not the north

 

[Golb]

Hang on, this can't be right. That means if you check it at 9PM and again at 9AM, north will be in a different place.

the sun will be in a different place, not the north ;-)

 

[user24]

Don't forget about the light saving time.

Yep, I'm accounting for that Good to keep in mind though.

the sun will be in a different place, not the north ;-)

Yes, the sun will be in a different place, but the hour hand won't be, so I'll make the bisection and end up thinking north's in a different place.

Here's a diagram illustrating my problem

If you apply the method in the morning and at the same time in the evening, your arrow will point in the opposite direction. In this diagram, the P.M. reading is correct, with the sun in the west, but the A.M. reading is incorrect, even though the exact same method is used at both times.

I can't reach any conclusion other than that 90% of the information on the web about this method is wrong.

There are a few ways I can see to correct for this:

1) Remember that the sun rises in the east and sets in the west and apply some common sense to the reading (perhaps only really applicable in morning and evening though.)

2) Adjust the method so you bisect the angle to create a north/south line, and in the morning north will be at the end of the line that is furthest from 12, while in the afternoon north will be at the end of the line closest to 12.

3) Adjust the method so you bisect the angle to create a north/south line, and in the morning count anti-clockwise from the hour until you reach the line to find north, and in the afternoon count clockwise until you reach the line.

4) Keep the method the same (count clockwise from the hour to the end of the line) and remember that in the morning that's south and in the evening it's north.

5) Or as Golb says below, remember that before noon North is to the left of the hour hand, after noon it's to the right of the hour hand.

 

[Golb]

You're right. Just checked the SAS survival handbook and in there they speak about the north-south-line. So they don't say what's North or south.
But you know what time it is, so before noon, south is on the right of the sun and in the afternoon south is on the left of the sun.

 

[user24]

You're right. Just checked the SAS survival handbook

I would have checked it myself but I'm moving house so it's packed

 

[ged]

TBH the wrist-watch method sucks. If you want to understand stuff like this a lot better, read this:

http://www.starpath.com/catalog/books/1830.htm

It's far and away the best book on navigation that I've ever read, and I've read shelves full.

The book is primarily aimed at marine navigation. Some of the techniques are a little unusual. Some will be looking for more precision than you'd probably need on land, they might use equipment you probably wouldn't have with you on land, and they might take more time than you'd want to take if you're on land, but much of the information is valuable anywhere, not just at sea, if only because of the insight and understanding that the author brings to the subject. He explains things very well, with some especially good diagrams. I've used some of the ideas to stay safe in some tricky situations on land using no navigational equipment at all -- just my senses.

After you've spent a few quality hours with this book you'll probably find yourself looking for navigational clues all the time, and wanting to use your watch to tell you your longitude to the nearest second.

That's about 61 feet in Northampton.

 

[user24]

Thanks ged, that looks like a good read. I'll put it on the list I do enjoy navigation, maps and map reading etc.

Yeah the wristwatch method does look a bit naff, but it's mentioned in a good number of places and I wanted to put it to the test a bit. One day I'll try to navigate using only that method to really put it to the test.

 

[forestwalker]

It also only works perfectly four times a year, an only if you have the correct *local* time (i.e. not the right time-zone, but the time of your exact location). The "wobbles" of the earth. But for finding a rought N-S line it works ok if you use it correctly.

And thanks Ged, now I have to buy *another* book. Looks interesting.

 

[santaman2000]

You're right. Just checked the SAS survival handbook and in there they speak about the north-south-line. So they don't say what's North or south.
But you know what time it is, so before noon, south is on the right of the sun and in the afternoon south is on the left of the sun.

They don't mention more than the N/S line because being written for the military, they may be operating in either the northern or the southern hemisphere where north would be reversed.

 

[Perrari]

Just tried this 7pm tonight, Point the hour hand to the sun & bisect the angle between the hour hand and 12 on your watch in a clockwise direction to get your North South line and it works fine. As the sun moves from East to West you should be able to say which is North & which is South. It was within a few degrees to the compass.

 

[ged]

Just tried this 7pm tonight, Point the hour hand to the sun & bisect the angle between the hour hand and 12 on your watch in a clockwise direction to get your North South line and it works fine. As the sun moves from East to West you should be able to say which is North & which is South. It was within a few degrees to the compass.

You were lucky today.

The value for the "Equation of Time" is around three minutes in late May. If you'd done the same thing on Valentine's day, it would be a quarter of an hour.

http://en.wikipedia.org/wiki/Equation_of_time
http://www.wsanford.com/~wsanford/exo/sundials/equation_of_time.html

This is one reason why the wrist-watch method sucks. It's all in that book I mentioned earlier.

 

[chilealan]

How accurate do you need to be? The sun rises in the East and sets in the west. So at 22.30 it is towards the west so stand with the Sun to your left and Guess where Nort is. At 12 noon stand with the sun behind you. which way are you looking. I will leave readers to work out the 6am situation. Again it depends how accurate you need to be.

 

[ged]

How accurate do you need to be? The sun rises in the East and sets in the west.

Well it does that on two days of the year, that is at the equinoxes.

Again it depends how accurate you need to be.

And your latitude.

Not only do you need to know how how accurate you need to be, but you need to know how accurate are your approximations, and where and when they can be used. The wrist watch method and the sunrise/sunset directions are approximations, and much of the time not good ones. There are parts of the world where at times they are of no use at all. In the arctic circles, at some times of the year the sun neither rises nor sets. Either it just goes around you all day, or you don't see it at all. In the tropics, the midday sun never strays far from overhead. Inbetween the tropics and the arctic circles, things can get intersting. It's all in the book.