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: Longitude by lunars during solar eclipse
    From: Peter Hakel
    Date: 2015 May 9, 20:08 +0000
    Hello Piero,

    I finally had some time to look into this and I don’t understand the following detail: the Sun and Moon semidiameters are both about quarter of a degree, so if the disks overlap their center-to-center distance cannot exceed (roughly) half a degree. How did you come up with a whole degree of centered lunar distance? Also, during a solar eclipse the near-limb distance is in fact negative.

    I’m also not sure how you used the lunar_distance.xls spreadsheet because it does not calculate longitude - it calculates Universal Time for checking or resetting one’s chronometer. If I wanted to extract longitude with available Navigation Spreadsheets, I would use the other lunar-distance spreadsheet, ld_prec.xls, in which I’d have to manually iterate on the longitude input (all other inputs are known) until the topocentric distance matches the observation (i.e., an exercise in modeling the Moon’s parallax effect). Such a result, however, would not have the highest accuracy, because this particular spreadsheet does not account for refraction.

    Peter Hakel

    Sent: Tuesday, April 21, 2015 12:36 PM
    Subject: [NavList] Re: Longitude by lunars during solar eclipse

    Hi Frank ,
    actually I used the excel file lunar_distance.xls as mentioned in the attached manual [*], after usual corrections due to T and pressure. My data :
    date = 3/20/2015 , 9h 2' GMT ; T=14° , p = 1021.4 mb ; elevation = 18. m ; sun low-limb ( sextant measurement ) = 38.° . GHA and declination from your nautical almanac . As the moon covered a large upper portion of the sun I assumed a lunar distance ( center to center ) of 1° .
    Since the excel wants far limb or near limb lunar distance I put in input , as near limb , 30' . Anyway I point out that "Easy lunars" ( in your web ) writes "This method is also prone to error when the lunar distance itself is below 15 degrees" .
    Thanks a lot for your helping .
    [*note from FER: the "attached manual" mentioned above was from Peter Hakel's navigation spreadsheets. Since it was irrelevant to this question and also carries a copyright notice, I have removed it]

    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