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    Re: DSLR Venus Lunar
    From: George Huxtable
    Date: 2010 Sep 16, 23:41 +0100

    Peter Hakel wrote-
    
    "I have a Davis Mark 15 with its one telescope and indeed Jupiter was just
    a blob of light, when I looked recently.  It has been my impression,
    however, (from reading about lunars, not shooting them much as of now...)
    that they are best observed with the maximum-magnification telescope
    available."
    
    ================
    
    That's rather a landsman's viewpoint. It would be better to say "the
    maximum magnification telescope appropriate in the circumstances". Which
    depend very much on sea state and size of vessel. It may be impossible to
    keep both targets of a lunar in view with a high-magnification telescope if
    the motion of the vessel is too wild.
    
    James Cook is on record as saying that he would often choose to observe a
    lunar without a telescope at all. He must have had a remarkably sharp eye.
    But it may also reflect on the optical standard of the telescopes of his
    day, the sea-conditions he was accustomed to, and the standard of precision
    in the result that he was prepared to accept.
    
    George.
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: "P H" 
    To: 
    Sent: Thursday, September 16, 2010 7:39 PM
    Subject: [NavList] Re: DSLR Venus Lunar
    
    
    |I have a Davis Mark 15 with its one telescope and indeed Jupiter was just
    a blob
    | of light, when I looked recently.  It has been my impression, however,
    (from
    | reading about lunars, not shooting them much as of now...) that they are
    best
    | observed with the maximum-magnification telescope available. From that I
    | concluded (perhaps incorrectly) that there are sextant telescopes
    available that
    | can sufficiently resolve planetary semidiameters so you can go
    limb-to-limb with
    | the Moon. After all, in lunar calculations we do account for the
    augmentation
    | effect on Moon's semidiameter, which is of the same order of magnitude
    (~0.1')
    | as the planetary semidiameters.  Now for Venus this would be a bit tricky
    since
    | both illuminated limbs would face toward the Sun (i.e. in the same
    direction
    | with Sun below the horizon), but for an outer planet like Jupiter I'd
    think it
    | would work.
    |
    | Can anyone confirm or correct my understanding of this detail?  I am
    pretty sure
    | that in the past Frank and others already commented on this rather
    | extensively...
    |
    |
    | Peter Hakel
    |
    |
    |
    |
    |
    | ________________________________
    | From: George Huxtable 
    | To: NavList@fer3.com
    | Sent: Thu, September 16, 2010 2:28:49 AM
    | Subject: [NavList] Re: DSLR Venus Lunar
    |
    |
    |
    | Meeus was writing for astronomers, who presumably have the sort of
    | telescope that can clearly identify those two radii; and not for the
    likes
    | of us, who in a sextant scope can only view such planets as a displaced
    | blob-of-light.
    |
    | [rest deleted by PH]
    |
    |
    |
    |
    
    
    
    
    

       
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