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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Orion North Arrow
From: Frank Reed
Date: 2022 Jan 13, 16:45 -0800

David Pike, you wrote:
"I’ve just tried it again, and the tail-end of the arrow allowing for the 8 degree’s twist, which is beneficial, still crosses my horizon at 160° true.  If I was made from rubber and could bend over double, my thumb would no doubt cross my horizon behind me at 340°, not much use to the night navigator."

You're doing it wrong :). You've created your own additional step, and it's not needed. At no point have I said that you should trace or extend anything down to the horizon. Try it again with a pencil instead of your thumb and forefinger. Hold the pencil in your first so that it's perpendicular to your extended arm. Aim at the North Arrow: tip on Mintaka (or a little left for added accuracy), eraser end on the tail of the arrow at the Orion nebula. No matter where Orion is in the sky, your pencil now points north, or if you prefer, its eraser points south. And yes, it really is just that simple. That thing you invented (why?) of extending something to to the horizon is un-necessary.

Maybe it would help if you reminded yourself how a 3-dimensional magnetic needle points, which I assume is something that you have looked at previously. If you have a magnetic needle that's free to move in three dimensions, it will float and tilt at some angle relative to the horizontal plane. The up-down tilt angle is known as the magnetic dip, but the projection of the needle onto the horizontal plane --its azimuthal direction-- still points to magnetic north. With the Orion North Arrow, the "pencil" (or other pointer, like your finger in the original instructions) doesn't need any adjustment. It already points very close to true north-south. The up-down tilt is your latitude, and the azimuthal direction is true north-south There's no additional step required to swing it down to the horizon line or whatever it is you're doing that's dropping you near 160° true. That step is your own augmentation, your own bit of roccoco, and it's entirely un-necessary.

Frank Reed

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