[quote=StarSailor;19000]Hi, I’m trying to teach myself celestial navigation. I’m at the stage where I’m trying to familiarise myself with the almanac and have been calculating the position of stars and going out and checking them, but I think I’m making some real dumb error.
Here’s what happened. Tonight I worked out the GHA and dec for Dubhe at 2015. They were about 151deg and 64 deg. (I verified these on the US navy’s online almanac too). So, I go outside and expect Dubhe to be at 151deg. But it’s not. It’s at something like 20deg west of N.
What’s my very basic error here? The GHA is the longitude, right? So the GHA of a star should be where it is on the compass rose, no?
I’m in the UK, btw[/quote]
Using your data, If Dubhe fell STRAIGHT to earth it would hit it’s Ground Point (GP) at Long 151W/Lat 64N, in Alaska. So if you’re looking at Dubhe from England it would look like about 340ish. You seem to have the wrong interpetation of the correct data.
It’s comendable you’re trying to get a holistic understanding of Celestial Navigation, that said, star Idetification/finding isn’t commonly done this way. Checkout a site called quitebay at this link; http://gcaptain.com/maritime/blog/celestial-navigation-101-star-identification/
Also, checkout the use of the Star Finder 2102D. And explore calculating the Azimuth and Altitude for the 57 Navigational Stars and Planets.
(another cool site I found: http://www.smithsofweston.com/NavMike.php