Re: Astronomical Quiz

From: S.Efimov (efim@aphi.kz)
Date: Wed Apr 20 2005 - 02:43:35 EDT

  • Next message: Fco. Javier Iruretagoyena: "Alldat.tle"

    English is not my native languige, and maybe I don't understand Jeff's
    hypothesis, but I reformulate it as following:
    Is there a point at the celestial sphere that never pass local zenith at
    darkness?
    My answer is No. If you are living at latitude teta (for example, at 10
    North), then you will observe at zenith stars with Dec=teta. Let's watching
    up at local midnights. Then during a year you will observe (if sky always
    clear, of course) ALL poins with this Dec, i.e. with all RA from 0 to 24h.
    Due to the Earth movement around the Sun every midnight the RA of zenith
    point will differ (from the same in the previous midnight) by about 4
    minutes, and this process is continuous.
    There is a special case for places where sometimes it is not dark at
    midnight, i.e. for high latitudes, but, I suppose, a long winter night
    darkness compensate this lack.
    
    Sergey Yefimov, Astronomer.
    Alma-Ata, Kazakhstan.
    
    ----- Original Message -----
    From: "Jeff Umbarger" <jumbarger2000@yahoo.com>
    To: "Tim Rogers" <timrogers@charter.net>; <SeeSat-L@satobs.org>
    Sent: Wednesday, April 20, 2005 11:03 AM
    Subject: Re: Astronomical Quiz
    
    
    > No, if I specified a point in the celestial sphere
    > (let's say RA 12h and Dec +10.0, then you could only
    > stand on 10.0N latitude to have the celestial point go
    > overhead. Let me clarify with a "bad" example: If the
    > point in the stellar field is where Sirus is (RA:
    > 6.75hr Dec.:-17.75deg) then you would have to stand on
    > 17.75 South latitude and wait until 6.75hr RA was
    > directly above (zenith). This will happen at slightly
    > different times throughout the year - sometimes in
    > darkness and sometimes in light. But there is one
    > point in the stellar field that is always over it's
    > corresponding point on earth (that is, a zenith to) in
    > light (that is, with the sun less than 6 degrees below
    > the horizon) for that point on earth. Where is the
    > point in the sky (not on earth!)?
    >
    > - Jeff
    >
    > --- Tim Rogers <timrogers@charter.net> wrote:
    >
    > > Just for clarification, would this be true for any
    > > location on the planet?
    > > When you say "when observed from directly below on
    > > the earth's surface," do
    > > you mean *just* below the earth's surface
    > > (centimeters or inches?)
    > >
    > > Tim Rogers
    > > Sugar Hill, GA  USA
    >
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