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: V corrections?
    From: David Pike
    Date: 2017 Mar 27, 02:25 -0700

    Mike.  Navigational tables can only give values in convenient steps, e.g. hourly or every degree.  If they had to give a value for every second of every day and/or every second of arc, the tables would be a mile thick.  Corrections like d and v are to help fill in the gaps.  For most astral bodies, ie the Sun, stars, and planets, GHA varies at a fairly constant rate, i.e. 15 degrees per minute, so you can use a simple arc to time table to work out GHA for intermediate times.  Because the Moon is a relatively close planet of the Earth, its change in GHA with time isn’t quite so constant, so if you’re using a simple arc to time table, this variation in rate has to be allowed for as an additional correction, hence the v correction.   When using the increments and correction tables (Appendix C in Mary Blewitt) to work out GHA Moon for an intermediate time, first look in the Moon column to get the basic arc to time for the Moon, then enter the last three columns with the v Moon value from the daily page to get the actual v correction to be added to the basic arc to time value.  Because the tabulated basic Moon arc to time value is its lowest possible value, the actual v correction should always be added, so Moon v is always positive.

    The best way to work most of this out is to download the full Nautical Almanac and HO249/AP3270 from the links given by Gary, because the explanations therein not only explain the tables but give worked examples of their use.  Also, having the whole thing in front of you enables you to explore any ‘what ifs’ which might crop up when you read them. As Gary says, some of the corrections made necessary by using the Nautical Almanac can be avoided by using the Air Almanac, which has ten minute rather than hourly values in the daily pages. DaveP

       
    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