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: Short Term Proper Motion
    From: Paul Hirose
    Date: 2019 Mar 12, 20:42 -0700

    On 2019-03-11 20:01, Bill Bertrand wrote:
    >    -- The j1991.25 Dec value is listed (it differs ~3x10^-5) degrees for the 9 year difference
    
    Here are Bellatrix data from the original (1997) Hipparcos catalog and
    the 2007 re-reduction. Values are RA, dec, parallax (mas), RA PM
    (mas/yr), dec PM at J1991.25. The RA and dec I have converted to
    sexagesimal at sufficient precision. Note that RA proper motion is great
    circle units, not coordinate units. I.e., the unit is the same size as
    the declination proper motion.
    
    081.28278416 +06.34973451 13.42 -8.75 -13.28 (1997)
    (05 25 07.868 +06 20 59.05)
    
    081.28278339 +06.34973457 12.92 -8.11 -12.88 (2007)
    (05 25 07.868 +06 20 59.05)
    
    I don't see those coordinates in the supposed Hipparcos data you quoted.
    Where are they?
    
    In addition, the "RA/Dec (on date)" aren't meaningful without knowledge
    of the basis of the coordinates — the stuff I mentioned in the previous
    message, such as astrometric place vs. apparent place and ICRS vs. true
    equator and equinox. Until you resolve that question, it's futile to
    compare those values to yours.
    
    Roger thinks they may be apparent place, but if so, they aren't very
    accurate — about 7 arc seconds from my computation with respect to the
    true equator and equinox.
    

       
    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