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: Star locations?
    From: Bill B
    Date: 2014 Sep 16, 16:34 -0400

    On 9/16/2014 2:01 PM, Samuel L wrote:
    > I'm beginning to understand it a little bit assuming that the
    > Constellation of Aries is the general equivalent to the Greenwich
    > meridian. Now if that's the case then I can figure it out.
    >
    > That something is located at/near/on the Vernal equinox might as well be
    > anywhere in the universe to someone that doesn't know what to look for.
    > Here's how I see things- this is September. Spring is a long time ago
    > and also in the future. So it's impossible to locate something at this
    > date based on that time....which I'm sure it's not.
    >
    Explanation from a Dummy:
    
    As a starting point, Frank mentioned "precession." Google that.
    Practically speaking where the north pole points star-wise changes over
    time, with a 26,000 year cycle. Currently Polaris is the pole star in
    the northern hemisphere. The pole does not point directly at it (note it
    has declination greater less than 90 so it circles the pole) but it will
    come closer to the pole (declination decreasing) over the next century
    or so. Then it will drift away. 3,000 years ago it was not our pole star.
    
    In essence the line for the equinox did pass through Aries at some point
    in time thousands of years ago, but due to precession it does not now.
    Back in the day (way back) when the man-made construct of degrees,
    minutes and seconds (sexagesimal system) used for latitude and longitude
    came into being, it did. The First Point of Aries became the landmark
    for SHA and RA, which as others noted is almost as arbitrary as the
    Greenwich meridian. It is, a least, and observable celestial event.
    Greenwich vs Paris? Political event. ;-)
    
    http://en.wikipedia.org/wiki/First_Point_of_Aries
    
    With that landmark, we can locate a star at any given point in time.
    Given other minor variables, the SHA of a star remains almost constant.
    (Look at the star tables, pages 269-273 in the almanac, and you will see
    a slight change in SHA and declination over the year). Much like the
    Sun's GHA, GHA Aries changes widely on a daily basis. Simply put, GHA
    Aries plus SHA star equals GHA star.
    
    You might also notice the almanac gives the SHA of planets in the lower
    right of the left daily pages, then wraps it up neatly with GHA Aries to
    give you an hourly GHA for the planets on the left page. As Jonathan
    pointed out, too much paper to do each star.
    
    AS a beginner I was confused by SHA and RA being given either in time or
    degrees and seemingly moving in opposite directions. (Hours are
    convenient for astronomers.) I'll let you do your homework on that one.
    
    http://en.wikipedia.org/wiki/Right_ascension
    http://en.wikipedia.org/wiki/Hour_angle
    

       
    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