Welcome to the NavList Message Boards.


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

Compose Your Message

Add Images & Files
    Re: Data reduction request
    From: Frank Reed
    Date: 2013 Nov 18, 16:36 -0800

    Richard Gaarden, you wrote:
    "I recorded three solar altitudes today. They are:
    66 41 53 Lower Limb {at} 15 13 37 GMT
    65 49 41 Lower Limb {at} 15 24 18 GMT
    64 23 21 Lower Limb {at} 15 39 36 GMT"

    Ok, so as I recall, you're in western Pennsylvania and that seems to match the coordinates you've given (but see below). If it's around 15 hours GMT, that makes it about 10:00 in the morning EST. Your "solar altitudes" are larger than 60 degrees and decreasing. These are presumably zenith distances (instead of altitudes), which is, I think, consistent with your statement that these observations were made with a theodolite.

    For the first observation, subtracting from 90°, I get 23°18.1' for the altitude of the Sun LL. Then I subtract 2.3' for refraction and add 16.2' for semi-diameter (ignoring solar parallax for now), which should then be comparable with the predicted Hc at the time of the sight. The result is 23°32.0'. But the predicted Hc for your location (from the USNO calculator page here: http://aa.usno.navy.mil/data/docs/celnavtable.php) is 23°35.2'. For the second observation, the corrected altitude is 24°24.3' while the predicted Hc is 24°30.3'. For the third altitude, the corrected altitude is 25°50.7' and the predicted is 24°40.6'. I could be wrong, and maybe I have mis-interpreted your input numbers, but those look like fairly substantial errors: -3',-6',+10'.

    By the way, you gave your latitude as "41 50 285"? I presume that's 41°50'28" What's the third number with three digits? It won't change the outcome much.


    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

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

    (please, no nicknames or handles)
    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 Settings

    Posting Code:

    Custom Index

    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