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Hey Jim, about that 4.5 degree to the West for magnetic declination. I wonder if thats why when i took my compass out lastnight and set Polaris in its sights, North was pointing off a little towards the West.

If I was bolting my pier down, would I follow what the compass seemed to indicate was North, or Just go by Polaris?

Id be lying If i said i wasnt just a tad bit stumped by the allowing for magnetic declination part.
I think its starting to make sense. I keep seeing Deans compass on his mount with the white line a little bit away from what his compass said was north.

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As you already know, Polaris is pretty close to the axis of the earth's rotation. However, magnetic north points to a location other than the axis of rotation.

Here's a little experiment to help you visualize it: Take and orange and draw a dot about 1cm from the stem at the top. That dot represents magnetic north, while the stem location is true north. Now imagine you are an observer at various locations on the orange. (yeah, you'd have to be really small!) At some locations, the true north and magnetic north locations would line up perfectly and appear the same. At other locations, there would be a larger difference between where your compass pointed and where true north actually is.

Bottom line, I'd go by Polaris because 1) you know true north is 4.5 degrees from magnetic north at your location, and 2) you don't know if your compass is accurate, so your bracket could possibly be off by more than 4.5 degrees.

Nice work on the observatory, by the way. I'm enjoying watching it come together.

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Edited by bdjeep (05/19/08 02:40 PM)

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