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
    Name or NavList Code:
    Email:
       
    Reply
    Distance by Vertical Angle
    From: Frank Reed
    Date: 2020 Oct 6, 11:09 -0700

    There are tables in various navigation manuals that will tell you the distance of a mountain peak or maybe a vessel when you measure the angular height of that portion of it peeking up from behind the horizon. These tables and their explanations have been wrapped in mystery and often confused by long-running errors. In my "Office Hours" session on Sunday, I spent some time on a little presentation trying to explain where the tables and equations originate and also, I hope, demonstrating their reasonable limit.

    I'll start this thread off with a scenario and an image to get you thinking...

    You are "shipwrecked" on an unihabited island paradise in the western Caribbean. You have lots of great books to read (and you haven't yet had that "Twilight Zone" moment where you break your reading glasses). There's lots of fresh water trapped in plastic bottles (trash) washed up in the wrackline. But food is running out. You have just finished roasting the last delicious lizard on the island. The island's cockroach population, formerly kept in check by the lizards, is booming, and paradise is getting pretty annoying. So you scan the horizon for ships, hoping to hitch a ride back to good old civilzation...

    You have a sextant with you with a good 7x scope on it, and on the horizon you spot a three-masted ship. It's a cruise for well-heeled tourists. In fact, you know this vessel! It is the SS Botany Buoy, and you happen to know that the top of its mainmast stands 105 feet above the waterline. With your sextant, you measure the angle from the sea horizon (which is in front of the lower portion of the vessel visually), and you hope to determine how far away it is before you start burning down the last tree on the island for a signal.

    Here is what you see...

    [more in the next message]

    Frank Reed

    File:


    File:


       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Get a NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID 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