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: Nocturnals
    From: Keith Lindsay
    Date: 2012 Jan 31, 12:01 -0000
    Wolfgang and Frank, as is common in such debates, the context is as important as the content.  The words in my first posting from "The correction for Polaris's circumpolarity ..... " are exactly from Bedini at page 230.  The context is the measurement of distance.
    A discussion of the mnemonic diagrams giving circumpolarity is found in Bedini at page 512 in the context of navigational instruments.  There is a diagram of an example 'roda'.  ( I understand the word 'regimentos' to apply to a table of the sun's declination.)
    A further discussion of the use of Polaris in finding position is found on page 508.  It does indeed show that Polaris was well understood a hundred and more years earlier than Columbus.   However, that is not the same as saying that it was used to find latitude.  I quote the paragraph that follows on page 508.
    "That there were people in Portugal capable of adapting astronomy to the needs of navigation is shown by early tables, such as the 1339 Almanac of Coimbra.  It seems more likely however, that the initiative in this innovation came from pilots, who would undoubtedly have noticed the difference in altitude of the North Star at Lisbon and in Guinea.  Latitude can be defined by the elevation of the polestar, but the procedures introduced by Portuguese pilots in the 1450s to check distance sailed in a north-south direction between two observation of the polestar have nothing to do with establishing the latitude, which indeed was not then marked on charts.  The difference in angle between the two observations was multiplied by 16 2/3 to give the linear distance in leagues (a figure later changed to 17 1/2, still an underestimate).  Observation was made with the seaman's quadrant, and in the early days of altura navigation, as it was called, it became the practice to mark on the scale the names of the various Capes, islands and landmarks whose star altitudes had been observed.   At the same time, astronomers at home were compiling lists of latitudes, which by 1473 had reached the equator.  It should be emphasised however, that until latitude navigation was introduced after 1485 (when Joao 2's mathematical commission worked out the procedures), altura navigation did not involve the concept of latitude."
    There is an example of a seaman's quadrant with these star altitudes marked upon it in the maritime museum in Barcelona.
    I concur that the claim made for Columbus is surprising but now you will have to debate among yourselves as I will be out of circulation for two months.
    as aye,  Keith
    ----- Original Message -----
    From: Frank Reed
    Sent: Tuesday, January 31, 2012 3:56 AM
    Subject: [NavList] Re: Nocturnals

    Wolfgang, regarding Keith's comment suggesting that the circumpolarity of the North Star was not known before Columbus, you wrote:
    "Well, Bedini was clearly wrong. The circumpolar motion was well known to Portuguese mariners before Columbus."

    I agree. And it's such a strange suggestion that I wonder if there might have been some editing error or mis-translation. Does anyone have access to Bedini's original statement here?

    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

    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