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: Rejecting outliers: was: Kurtosis.
    From: Lars Bergman
    Date: 2011 Jan 2, 14:40 -0800

    I agree with George's analysis of Peter Fogg's data from 2007. Regarding the slope, which George questioned, I have come to the conclusion that 32' in 5 minutes of time seems correct. With the given altitude and latitude and knowing the declination of Canopus to be around 53 degrees south, you'll find the LHA to be around 339d with an azimuth of around 149d. Increasing LHA with 1d15.2' for 5 minutes change of GHA Aries gives an altitude that is 32' greater. I cannot see that Peter's mistake in plotting the slope as 34' instead of 32' makes any difference when it comes to "defining" observation 1 and 3 as outliers. With either slope those observations have the largest distance from the slope line.

    What strikes me is the large "spread" of the observations. If all observations are transposed (don't know if this is the correct term) to a common instant of time, by moving each of them along a line of 32'/5m slope, it is found to be some 13', with #1 the largest and #6 the smallest. This is of course reflected in the standard deviation value as well. It must have been rough conditions (provided the instrument didn't have any loose screws). Thus I would be more suspicious about the "low" altitudes (# 5,6,7,8). Large seas or swells may very well obscure the horizon, making the sights too small, rather than the opposite. So maybe #1 and 3 are the best sights ... But this is of course pure speculations from my side. Anyway, I cannot see that #5 is excellent, 1 and 3 poor and the rest mediocre. I would say that the average value of all sights is the best choise possible, and I would have kept in mind the large spread of the observations when evaluationg the resulting LOP. You don't need to calculate the spread, just look at the numbers: #2 is expected to be some 3' larger than #1, actually is it 4' less; # 3,4,5,6 are nearly flat where you would expect an increase of some 10' between #3 and 6.

    Lars 59N, 18E
    ----------------------------------------------------------------
    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