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: Vernal equinox
    From: Bill B
    Date: 2014 Mar 21, 20:20 -0400

    On 3/21/2014 6:06 PM, Peter Hakel wrote:
    > Declination is measured against the celestial equator - are you
    > referring to precession and nutation?  Can you point me to H. Prinz's
    > original postings?
    I can do better than point you. Below is the text. The text is also
    attached as a ms word.doc, and the diagram as a jpeg. Dug them up this
    AM from and old machine. Honestly, there was a term I had to Google at
    the time in an attempt to grasp Herbert's scholarly explanation.
    All said and done, it fell into my "things I didn't know I didn't know"
    sphere of ignorance. :-)
    Oops! You are some 5 minutes early. The correct value is 18:25:33. If
    you compute this from the N.A. you should be able to get the time within
      an accuracy of better than 15 seconds. I don't have a N.A. handy to
    check it out.
    In sync with the equinox related traffic that occurs with a period of
    0.5 tropical years on this list, I posted a diagram showing the apparent
    place of the sun around today's equinox with respect to the two
    fundamental reference frames:
    In the diagram, the ecliptic is blue. The true equator and equinoctial
    colure of date are green. The Sun (painted red) moves currently on a
    parallel of ecliptical latitude of -0.7".
    At 18:25:26 UT the Sun hits the equinoctial colure (i.e. R.A. = 0) at a
    declination of -0.73". At 18:25:33 UT it reaches ecliptical longitude 0.
    This is equinox.. At this point the decl. is 0.62" At 18:26:10 UT the
    sun reaches declination 0, at a longitude of 1.5" and a R.A. of 0.1s.
    All data computed with MICA Vers. 2, U.S.N.O.
    Conceptually, equinox implies that the declination of the sun equals
    zero. Hipparchus supposed this to happen in the equinoctial point, i.e.
    at zero longitude. When it was realized after Newton that the apparent
    Sun does not necessarily have to move through the equinoctial point each
    year, one had to make a decision whether to choose zero longitude or
    zero declination for the definition of equinox. Longitude was more
    How come the Sun has latitude? Hint: The latitude of the Sun is always
    very roughly (give or take 0.2") that of the Moon, divided by 32000.
    Have fun.
    Herbert Prinz


    File: 127334.equinox.doc
    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