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: Sine curve to approximate declination
    From: Trevor Kenchington
    Date: 2004 May 19, 21:13 +0000

    Frank Reed wrote:
    > A big part of this error results from the fact that the ecliptic only
    > looks like a sine curve. It's not a bad approximation, but the real
    > curve has "broader shoulders" than a sine curve. It's easy to see this
    > by imagining what the ecliptic would look like if the Earth's axis were
    > tilted, say, 80 degrees instead of 23.45.
    It may be easy for you to visualize that but I'm afraid I can't see it.
    I can visualize how things would be if the Earth's axis lay in the plane
    of the ecliptic (i.e. a 90 degree tilt), since that reduces to 2D
    geometry. But in that most extreme case, and assuming a perfectly
    circular orbit, I think declination would change linearly from solstice
    to equinox and vice versa -- meaning that the curve would have "narrower
    shoulders" than a sine curve.
    Can you explain how you see the "broader shoulders"? Or does the
    explanation lie in the departure from circularity of Earth's orbit?
    Trevor Kenchington
    Trevor J. Kenchington PhD                         Gadus{at}iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

    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