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: At the centre of time
    From: Frank Reed
    Date: 2009 Oct 24, 19:06 -0700

    Gary, you wrote:
    "Get in a French car and you will see a speedometer marked in kilometers per 
    hour and a tach marked in RPM. Trouble is neither is an SI unit. The proper 
    units should be meters per second and radians per second (there are no hours 
    or minutes in the SI system)."
    
    Good point. 
    
    Speaking of meters per second, has anyone else noticed an annoying tendency 
    among oceanographers to express ocean current speeds in meters per second? 
    Why can't they just use knots like everybody else? :-) And when converting in 
    my head to knots I always find myself stumped for a moment or two trying to 
    remember whether I should divide by two or multiply by two (two knots is very 
    close to one meter per second). 
    
    For angular frequencies, the proper SI unit for a rotation frequency is 
    presumably just "per second" (inverse seconds) rather than "radians per 
    second" since radians (and likewise degrees, minutes, and seconds) are not 
    units at all. They're just number labels like the words "percent" and "a 
    dozen" and "a gross".  I keep myself entertained by thinking about this 
    radians versus percent thing every time I come down the steep slope of the 
    Poconos when driving east on I-80. There are signs for steep highway slopes 
    given as percentages, e.g. "6% grade". How different would it be if it said 
    "0.06 radians grade"? Yes, I do think about these things... Pennsylvania is a 
    boring drive.
    
    You concluded: 
    "If even the French can use non SI units when it makes [sense] to do so then 
    it is OK for the English speaking world to do the same."
    
    Yep, and if French astronomers, who are "vraiment serieux", use parsecs and 
    mega-parsecs for distances when petameters are zettameters are readily 
    available for those scale ranges, then I think we can safely admit that 
    sometimes convenience and convention wins out over purism.
    
    -FER
    PS: Another word that's just a label for a count, much like our "dozen", is 
    the Mayan word "baktun" which is the same as saying "a dozen dozen thousands" 
    with fewer syllables... We're nearing the end of the 12th numbered "baktun" 
    of the Maya calendar. Unfortunately, this one only goes up to 12. The system 
    tops out at 12. So they either need to modify the calendar, or maybe it's the 
    end of the world ;-). And hey, that's another movie connection, but a silly 
    one, so I'll send you to a nice Wikipedian summary of the calendrical issue: 
    http://en.wikipedia.org/wiki/2012_phenomenon
    
    
    
    
    --~--~---------~--~----~------------~-------~--~----~
    NavList message boards: www.fer3.com/arc
    Or post by email to: NavList@fer3.com
    To unsubscribe, email NavList+unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    

       
    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