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: Aldebaran occultation
    From: Brad Morris
    Date: 2017 Mar 5, 22:40 -0500
    Alex

    I note that you provided your position to the nearest 0.1'.  

    Could you return to the spot and get a more precise answer?  With greater numbers of GPS satellites involved in the fix, the error in the fix diminishes.  Long term averaging, if your device provides it, also improves the accuracy.

    I don't know how sensitive the parallax is in the occultation situation but it occurs to me that this could be an additional source of error.

    0.1' = 182.5 meters

    At 40°27.2'N, that's a variation of 139/2 meters in longitude (0.05' in E/W from your meridian)

    In latitude, there is no reduction.

    At the most extreme location, you can still conceivably be
    Sqrt (139^2 +183^2) / 2 = 115 meters from the given position, and still not have to change the last digit.

    That is 40°27.2' N +/- 0.05'  86°58.8'W +/- 0.05'

    It may be worthy of experimentation to adjust the position of observation within those parameters to see the effect of parallax on the occultation.

    Frank has indicated the error due to limb roughness could be as much as 0.3'. (If I have misquoted you Frank, please jump in!)  However, that's limb position non specific.  We would need to know the roughness at the specific limb location, given your observation of Alderbaran and Moon contact.  

    In 1916, when stranded on the ice in the Antarctic night, Worsley and Reginald James rated the chronometers using occultations. In Shackleton's 'South', Appendix 1 Reginald James makes the assertion.   I've always been quite interested in occultations as a result.  Not for probing the shape of the limb, but as a tool for determining longitude or time.  

    Brad

















    On Mar 5, 2017 8:29 PM, "Paul Hirose" <NoReply_Hirose@fer3.com> wrote:

    On 2017-03-05 14:03, I wrote:
    > On 2017-03-04 22:48, Alexandre Eremenko wrote:
    >> The moment of disappearance I timed as March 5, 3:56:48 (GMT)
    >>
    >> 40d27.2'N, 86d55.8'W
    >
    > My Lunar4 program says Aldebaran is .02′ inside the Moon's limb at that
    > time. It puts the occultation 4 seconds earlier.
    
    The USNO MICA program agrees with Lunar4. Topocentric coordinates of
    both bodies from MICA:
    
    267.63519° 61.59173° Moon az, ZD
    267.71641° 61.33040° Aldebaran az, ZD
    
    That equals .27090° separation angle. MICA says semidiameter is 16′
    16.4″, which is .020′ greater than the separation angle.
    
    However, neither program accounts for the irregularities in the Moon's
    limb, which I believe are significant at this precision. My
    computational tools are not accurate enough to find any error in the
    observation by Alex.
    
    


       
    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