Measuring Latitude by Polaris

From the Paper Plate Education Web Site. See http://analyzer.depaul.edu/paperplate/Latitude%20by%20Polaris.htm

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[llamanator3000]

grrr, already know this, what I want is how to adjust for the error since the gp of polaris isn't exactly north

[bbeckwin]

One way to correct of the fact that Polaris is not exactly on the North Celestial Pole is to use the star Kochab, which is the second brightest star of the Little Dipper after Polaris. A straight line from Polaris to Kochab intersects the North Celestial Pole. So to find the exact location of the Pole you can follow this line to a point about 3/4 of a degree from Polaris.

[gamesbok]

For latitudes south of the equator I presume some sort of drilling rig would be required to facilitate observation.

[Mardevscience]

I'm an Earth Science teacher and I always have the hardest time getting the kids to comprehend this. THIS IS AMAZING!!! It covers everything I want them to understand! THANK YOU THANK YOU THANK YOU!

[polarkerr]

Very nice explanation, some need to know how to find Polaris" Great bear etc..)

Thanks

[pmh099]

The Nautical Almanac has a table for that very purpose. Astronomical Almanacs have one too, I believe. You will need to know at least an approximate value for the LHA (local hour angle) of Polaris. This determines how far "above" or "below" the Pole Polaris is located at that moment, and hence the size of the correction.

[interstitialofficial]

Do you have to label every single line with an, "N"?

[llamanator3000]

thank you very much! Not only did you teach me the name of a star that was previously nameless to me, but you've helped me with my bigger goals. If you happen to have any further resources in regards to celestial navigation, and have the time and inclination, please drop me a message, my goal is to be competent in navigation by spring so I'm ready for next year's boating season. You've been more than enough help already, however, and again, thank you very much.

[bbeckwin]

Exactly! It's just as easy to make the correction when Kochab is below Polaris, in which case your latitude would be 39.25 deg if your astrolabe measurement of Polaris was 40 deg. Navigators used so-called nocturnals to measure the correction at any time, not just when Kochab is above or below Polaris.

To see an example of a nocturnal, simply google "Solid Brass Nocturnal." (I tried to include the URL, but I don't think YouTube allows the inclusion of URL's in comments.)

[llamanator3000]

I'm asking this because obviously even the north star rotates around the celestial pole, and if you're saying that the north pole is .75 degrees between polaris and kochab, then when kochab is at it's highest, polaris should be .75 below the actual north right? at which point you can measure polaris and then make your adjustment? at any other time polaris would have moved slightly, if undetectable by the naked eye, and make correcting the error more difficult right? please correct me if wrong

[llamanator3000]

thank you so much. A degree might not seem like much but if you're trying to hit an island while sailing, or avoid shoals, it could mean everything couldn't it? Not that you'd just use latitude from Polaris to navigate, but no reason to be sloppy with anything in this regards.

so when Kochab has culminated would be the best time to check your latitude then? and then say Polaris is 40' your lat would be 40.75'? am I grasping that correctly?