Finding South with a Wristwatch

[Paradox]

I was rereading some old threads and recalled a method for finding South using the sun and an analog wristwatch that I learned many years ago from a source I have forgotten.

Its easy: point the hour hand at the sun, South will be halfway between the hour hand and the "12"



In the example above it is 2:50 in the afternoon (standard time), the hour hand is pointed at the sun. South is found at the angle bisecting 2:50 and 12 or at 1:25 pm.



You must correct for daylight savings time. In the example above it is 9:30 am DST, so the standard time is 8:30 am. Hence 8:30 is pointed at the sun and south is found at 10:15 am.

 

[mahony]

Cool, but I guess I don't really need a watch...I just have to know what time it is, which I can judge from the sun!

 

[MichaelJ]

Neat trick! I assume it only works in a certain latitude range in the northern hemisphere?

 

[Tom Rankin]

Neat trick! I assume it only works in a certain latitude range in the northern hemisphere?

Yeah, try that at the equator! Although, it should work quite well at the North Pole.

 

[mahony]

Hey wait a minute...if you're at the North Pole all directions are South anyway!!!

 

[DougPaul]

An old trick, but it may be difficult for all those young'uns who may never have owned an analog watch.

And if you had a 24hr analog watch, you could save all that nasty bisecting...

It can work close to the equator, but you need to hold the watch parallel to the plane of the sun's apparent movement (parallel to the plane of the equator should be good enough). Aim 3 and 9 at the horizons.

You can reverse the process to tell the time with a compass. Hint--the earth rotates 15 degrees/hour.

But then again, those newbies with their GPSes can determine direction and just read off the time. (And get location as a bonus!)

Doug

 

[DougPaul]

Hey wait a minute...if you're at the North Pole all directions are South anyway!!!

If you know the time and the sun direction, you can determine which south is which. (Ie do you want to go to Greenland or Russia?)

Finding the sun direction can be difficult near the poles due to it being just over the horizon or obscured by haze and clouds. Polar explorers use a sky compass which senses the polarization of scattered light from above to determine the direction of the sun. http://www.gi.alaska.edu/ScienceForum/ASF8/865.html (This is related to photographers' use of polarizing filters to remove haze.)

Magnetic compasses are also not very reliable in the far north--the suffer from very high declination (magnetic north near the North Pole is south toward northern Canada) and can be affected by solar weather (the aurora, etc).

Doug

 

[Paradox]

Dang! That's right. I'll change the photo tonight.

 

[SAR-EMT40]

You must correct for daylight savings time. In the example above it is 9:30 am DST, so the standard time is 10:30 am. Hence 10:30 is pointed at the sun and south is found at 11:15 am.

If its DST wouldn't 9:30am DST need to be corrected to 8:30am EST?

Keith

 

[DougPaul]

Dang! That's right. I'll change the photo tonight.

Just change the text: 11:30 DST -> 10:30 ST and the photo becomes correct.


FWIW, I learned a slightly different version of this technique: point the bisect (between 12 and the hour) at the sun and 12 points south. The angle is the same as your version, but the watch stays at a constant orientation throughout the day.

Doug

 

[forestgnome]

Encyclopedia DougPaulica

Thanks for all that you contribute...mindblowing

happy trails

 

[Little Rickie]

Cool, but I guess I don't really need a watch...I just have to know what time it is, which I can judge from the sun!

Now that's just too simple to have any fun with while on the forum.

 

[J.Dub]

An old trick, but it may be difficult for all those young'uns who may never have owned an analog watch.

In what orientation to the sun should I hold my iPhone...?

 

[Chip]

In what orientation to the sun should I hold my iPhone...?

You need to hold the phone outstretched between your eyes and the sun which will create a long thin shadow behind you. Prior to that you should have constructed a sun dial array. Now note where the shadow lies. Obviously now, knowing the time, you can determine the direction you are facing...

or "there's an app for that."

 

[DougPaul]

An old trick, but it may be difficult for all those young'uns who may never have owned an analog watch.

In what orientation to the sun should I hold my iPhone...?

You mean there is no sundial app?

Doug