NavList:

I didn't realize at the time (many years ago) I made these modifications that the ecliptic, due to the
projection used for the star base, would plot as a circle which makes it much easier to place on the
star base. The radius of the ecliptic is 90° on the declination/latitude scale 
and the center is placed on the
arctic circle at its intersection with the right ascension of the the sun at 
the time of the winter solstice
which is 270° on the star base. To determine where to place the center of the 
ecliptic I placed a straightedge
from 90°   to 270°  and drew a line extending from about 70°
   north to about 30° south. I placed the red disk over it and marked 23.5°
   south. I then set the drawing compass to extend from the pole to the 
equator and swung an arc from 23.5°
   south so that it placed a mark on the line at 66.5° north. Then I used this 
mark as the center to draw the ecliptic,

See:

http://fer3.com/arc/m2.aspx/Star-finder-2102D-further-modification-LaPook-nov-2010-g14300

From: Gary LaPook <garylapook@pacbell.net>
Subject: [NavList] Re: Yet another modified 2102-D star finder
To: NavList@fer3.com
Date: Tuesday, January 8, 2013, 2:07 AM

See http://fer3.com/arc/m2.aspx/Modifications-2102D-LaPook-apr-2009-g7982 http://fer3.com/arc/m2.aspx/Modifications-2102D-LaPook-apr-2009-g7986 gl --- On Tue, 1/8/13, Gary LaPook <garylapook@pacbell.net> wrote: From: Gary LaPook <garylapook@pacbell.net> Subject: [NavList] Re: Yet another modified 2102-D star finder To: NavList@fer3.com Date: Tuesday, January 8, 2013, 12:01 AM Try these too. H.O. 2102-D http://www.fer3.com/arc/imgx/IMG_0148.JPG http://www.fer3.com/arc/imgx/IMG_0151.JPG http://www.fer3.com/arc/imgx/IMG_0153.JPG http://www.fer3.com/arc/imgx/IMG_0154.JPG http://www.fer3.com/arc/imgx/IMG_0159.JPG http://www.fer3.com/arc/imgx/IMG_0160.JPG http://www.fer3.com/arc/imgx/IMG_0161.JPG http://www.fer3.com/arc/imgx/IMG_0162.JPG gl --- On Mon, 1/7/13, John Forrest <londonjf@yahoo.co.uk> wrote: From: John Forrest <londonjf@yahoo.co.uk> Subject: [NavList] Yet another modified 2102-D star finder To: NavList@fer3.com Date: Monday, January 7, 2013, 10:52 PM I'm not sure if I've not re-invented the wheel here, but I've modified a 2102-D to make it easier to use - even if perhaps less accurate - than the instructions in Burch's book. I wanted something where I could track the sky over time and I think I've achieved that. I have to say I was attracted by Byron Franklin's version, but have to treat this as not obtainable. I was trying to see what I could thus do on a 2102-D itself. My approach is to introduce what I term the "Hours Disk" - an extra disk I make by cutting up an OHP slide, with the hours marked every 15 degrees going anticlockwise (for northern hemisphere). The setup task is to put "midnight" at the correct place for the longitude in question - effectively taking GHA(Aries) for UST/GMT midnight on the day in question and subtracting the longitude in degrees. You move the 00 hours marker to point at this calculated value (I call it the ZeroPoint), and then point the arrow on the horizon disk to the appropriate time - you use the degree markings on the base disk to give minutes of time, and if you so desired can easily go to the nearest minute. Unlike the Burch approach, but like the Franklin one, you can track movement by just moving the arrow to the new time - the ZeroPosition is effectively good for a day assuming you are stationary, and even if you are moving, the updates should not be that hard. Unlike Byron's star finder, this approach is not self contained - you need an almanac of sorts. However, I have a simple table I dub the "RoughnReady Almanac" which contains average GHA(Aries) figures for the first day of each month given to the nearest degree, and this seems to work reasonably well. The whole approach is not that accurate, but as far as I can see the 2102-D starfinder is not that accurate to start with nor I assume was it originally supposed to be. I think my results are only good to a few degrees. However, the important bit is that it is fast - while I'd not necessarily claim 2 minutes, it seems similar in time to Byron's. I've written up this approach on http://easystarfinder.blogspot.co.uk. There are some photos there too, as well as a link to the RoughnReady almanac. I'm a rank amateur in this area, but the approach seems valid for me. Comments anyone? Have I missed something obvious? ---------------------------------------------------------------- NavList message boards and member settings: www.fer3.com/NavList Members may optionally receive posts by email. To cancel email delivery, send a message to NoMail[at]fer3.com ----------------------------------------------------------------