Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Astra IIIb: First Impressions
    From: Frank Reed
    Date: 2014 Mar 11, 19:05 -0700

    Sean, you wrote:
    "As for the index error, I was very careful to read the off arc number correctly, subtracting the indicated minutes value from 60."

    Well, so much for that theory! :) Since you're doing that part right, there may be something else going on. It certainly looks like you've got a net systematic error remaining, and the IC is the most likely culprit. Then again, the apparent systematic error in a set of only five observations could be random chance in a moderately noisy set of observations.

    And you added:
    "I have since attempted to adjust the index error out. I will be taking some more sights soon to see if that improves my results a little. "

    Of course, once you adjust, it changes everything. So you should at least expect a different systematic error. As for adjusting it out, as you know (I am sure), there's no strong reason to eliminate it. But many people do prefer to keep it under one minute of arc. Both for practical observations and also for teaching purposes, it's nice to be able to read the angle and then be done with it. It saves a step when you're not interested in those fractions of a minute of arc.

    I've describe many methods over the years for getting a better IC. Among that various options, the best I've found is simple magnification. Set your sextant on its side on a table pointed at a distant sharply-defined, vertical mark, like a radio tower or a mast. Then remove the standard sextant telescope. Place a small spotting scope (something with a magnification in the range from 25x to 40x) in line with the normal position of the sextant. Then align the direct and reflected images of the distant vertical mark as usual. You should find that you can get the IC within +/-0.1' over and over again.

    You wrote:
    "And finally, regarding the use of an exclamation point as both decimal and minute indicator: I had never seen this until I came here"

    I'm not surprised. I do remember some relative newcomer asking some NavList regular about those "odd exclamation marks" within the past year or two. Maybe that was you. There's jargon that's part of the culture --that we need for practical reasons, and then there are just weird old habits. I contend that the exclamation marks fall in the latter category.

    -FER

    ----------------------------------------------------------------
    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
    ----------------------------------------------------------------

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site