Angle of Incidence

[Robust]

I want to cut the end of a piece of lumber at an angle coincident with that which is projected by shadow when the sun is at a specific distance on the diurnal arc relevant to magnetic North. I read some time ago of a method but forgot. Your help, please.

[C1ay]

I want to cut the end of a piece of lumber at an angle coincident with that which is projected by shadow when the sun is at a specific distance on the diurnal arc relevant to magnetic North. I read some time ago of a method but forgot. Your help, please.

There are many sources on the web to find how to calculate the solar azimuth, just google that phrase. Likely none will account for the magnetic deviation since it is always changing and is different from one longitude to the next. You can google that phrase as well to find magnetic deviation maps for your area.

 

FWIW, your angle will be coincident for now but not for the duration of time since the magnetic poles are on the move.

[Robust]

Clay, I know the azimuth and time of its occurrence. There is a simple and accuraste way to transpose that information to the angle that I want to cut my piece of lumber. That is what I'm after.

 

They wrote a song about it: "The Shadow of Your Smile" - or something like that....

[Qfwfq]

Cast a shadow when the sun is right there and tie a string to use as a reference for the cutting. :xx:

[C1ay]

Cast a shadow when the sun is right there and tie a string to use as a reference for the cutting. :xx:

BUt how does one cast a shadow relevant to the magnetic poles?

[Qfwfq]

Honest, I hadn't notice Robust said magnetic north!!!!!! :xx:

 

:xx:

[Robust]

Cast a shadow when the sun is right there and tie a string to use as a reference for the cutting. :)

 

Yes, Qf, that's the principle it seems. I'll keep looking for the original article and keep monkeying with it in the meantime.

[C1ay]

Yes, Qf, that's the principle it seems. I'll keep looking for the original article and keep monkeying with it in the meantime.

You do realize that such a shadow would be cast realtive to true north or true south, not relative to magnetic north as you inquired? In some locations the difference between true north and magnetic north can be greater than 50°. Here's a global chart.