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    Re: JPL ephemeresis and Nautical Almanac - speed of light question
    From: Mike Mayer
    Date: 2018 Apr 3, 07:24 -0500



    You are correct. Once you know the locations of earth and the object in question you compensate for the time the light takes to travel from the object to earth. I’m familiar with the Meeus book (Astronomical Algorithms by Jean Meeus) and it is in Chapter 33 on page 224. He calls it “light time”.





    From: NavList@fer3.com <NavList@fer3.com> On Behalf Of Rafal O.
    Sent: Tuesday, April 3, 2018 3:31 AM
    To: mwmayer{at}tds.net
    Subject: [NavList] JPL ephemeresis and Nautical Almanac - speed of light question



        I am thinking more and more about writing my own program that generates Nautial Almanac entries for a given date. I want to use JPL ephemeresis (still trying to figure out how to extract these data, I should read Fortran code I think). Nevertheless, I have a question, maybe naive. Namely, let us calculate position of i.e. Earth and Sun at a given time moment t. We can calculate declination and GHA but the obeserver will not see it at this moment of time but raher 8m20s later (due to time needed to reach light ray emited by Sun). I think that the same occures for all other celestial bodies. The reflected / emited light and time needed to reach the observer should be taken into account. Am I correct?

    Best regards,

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