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    Re: Santa Barbara 2016: Venus sight
    From: Peter Hakel
    Date: 2016 Dec 20, 00:48 +0000
    Stan,

    On this issue I have no comment, since for “Astron” I am just a messenger for “an anonymous benevolent user” who created this spreadsheet; my original spreadsheets do not calculate twilight info.


    Peter Hakel



    From: Stan K <NoReply_StanK@fer3.com>
    To: pmh099---.com
    Sent: Monday, December 19, 2016 10:38 AM
    Subject: [NavList] Re: Santa Barbara 2016: Venus sight

    Peter,

    I've been trying to send this privately, both on and off NavList, but the messages keep getting returned.  I thought you might have changed you address because of the Yahoo hack, but your messages seem to be coming from the same old address.

    Anyway, I have a question about the way Astron defines twilights.  All the definitions of twilight, whether civil or nautical (or astronomical) that I can find involve the sun, rise or set.  Morning twilight starts at the start of AM nautical/civil twilight and ends at sunrise.  Evening twilight starts at sunset and ends at the end of civil/nautical twilight.  Astron seems to define AM twilight as starting from the start of AM nautical twilight and ending at the start of AM civil twilight; PM twilight starts at the end of PM civil twilight and ends at the end of PM nautical twilight.

    If there is a reference that defines twilights this way, please let me know what it is.

    Stan






       
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