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    Orion North Arrow
    From: Frank Reed
    Date: 2021 Feb 22, 19:52 -0800

    With Orion near the meridian in early evenings this time of year, it's a good time bring up the Orion North Arrow again.

    You point your index finger at Mintaka. You hold your thumb perpendicular to your index finger and aligned with the axis of the arrow. Then your thumb is pointing north and inclined at an angle to the horizontal plane that is equal to your latitude. You can clean things up a bit by using a playing card in place of your fingers. Hold the card out in front of you with the long edge on the "upper" side aimed at Mintaka. You're looking at the card edge-on with the short edge of the card towards you. Turn the card until it's aligned with the axis of the arrow. If precision matters, rotate an extra 8° counter-clockwise since the alignment of the Orion North Arrow isn't perfect. The short edge of the card is now equivalent to your thumb in the original setup: the short edge of the card points north, and it is inclined at an angle relative to your local horizontal plane that is equal to your latitude. Either your thumb or that card edge are aligned exactly the same as the gnomon of a sundial, aiming very nearly at the position of the North Star in the sky. This works anywhere on Earth.

    More description, more images, and some example cases from my post from four years ago:

    Frank Reed
    PS: This is old navigation lore, and you may not have heard of it. But don't take my word for it. Here's British astronaut Tim Peake describing it for a recent BBC talk show:


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