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: Dropping leap seconds and the impact on celestial navigation
    From: Fred Hebard
    Date: 2011 Sep 12, 10:15 -0400

    Frank,
    
    I know what you are saying is correct, but it is deliberately misleading, in my opinion.
    
    Fred
    
    On Sun, Sep 11, 2011 at 11:31 PM, Frank Reed  wrote:
    > Fred, you wrote:
    > "I believe you're exaggerating with statistics comparing the suns' position at 
    > noon EDT to noon time in Philadelphia, PA."
    > 
    > Where's the exaggeration? It's a simple fact: for 65% of the year, states 
    from Maine to Indiana keep time that would correspond to mean solar time at 
    60 degrees longitude (the fraction of the year was 57.5% before 2007). On any 
    of those 238 days out of the year, when a clock in Pennsylvania or Ohio or 
    most of Michigan or Indiana reads 12:00 noon, the Sun is over the 60 degree 
    meridian of longitude well out into the Atlantic (actually due to the 
    equation of time for the period in question, it varies from about 58.5 to 
    about 64.0 degrees longitude).
    > 
    > Consider Columbus, Georgia. Most people think of Georgia as an eastern state 
    because it's on the Atlantic coast. But as originally drawn, most of Georgia 
    should be in the Central Time Zone. Instead it's all in the Eastern Time 
    Zone. At 85 degrees west longitude, Columbus, GA is ten degrees of longitude 
    or forty minutes in time away from the normal center-line of the Eastern time 
    zone. Since it's on EDT (equivalent to AST) for 65% of the year, the Sun does 
    not reach the meridian in Columbus, GA until 1:40 in the afternoon, on 
    average. Clocks are "disconnected" from Sun time by 1h 40m (ranging from 1h 
    35m to 1h 45m during the spring and summer but decreasing to 1h 24m around 
    November 1, and then of course for the four months when DST is not used it 
    ranges from 24m to 39m). When the clocks in Columbus read 12:00, it is never 
    local apparent noon on any day of the year.
    > 
    > You added:
    > 
    > 
    > "The proper comparison is noon EST, which goes to 75W, within a few miles of Philadelphia, PA."
    > 
    > That's the proper comparison for less than 35% of the year as the rules 
    stand today. For MOST of the year (238 days), the eastern states and eastern 
    midwest states of the USA keep Atlantic Standard Time. We LABEL it Eastern 
    Daylight Time for various reasons, but that changes nothing: EDT=AST.
    > 
    > -FER
    > 
    > ----------------------------------------------------------------
    > NavList message boards and member settings: www.fer3.com/NavList
    > Members may optionally receive posts by email.
    > To cancel email delivery, send a message to NoMail[at]fer3.com
    > ----------------------------------------------------------------
    > 
    > 
    > 
    > 
    > -- 
    > Keeping up with the grind
    
    
    
    
    

       
    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