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star motions

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  • Diana K Rosenberg
    Fixed star motions answered Posted by: Arthyr awc99@mindspring.com kaldu4you Date: Fri Sep 1, 2006 11:11 am (PDT) Arthyr sent: In my opinion we use
    Message 1 of 2 , Sep 1, 2006
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      star motions

      Fixed star motions answered
          Posted by: "Arthyr" awc99@... kaldu4you
          Date: Fri Sep 1, 2006 11:11 am (PDT)

      Arthyr sent:

      In my opinion we use precessional motion of one degreee every 72 years. . .
      just looking for confirmation. . .
      ===============================================
      Precession is 0 deg 0 min 50.23 secs a year

      Rule of thumb, 5 minutes of a degree every 6 years

      1 full degree every 71.67 years (72 is fine as an average)

      As for stars' proper motion, it is extremely slow and each star has its
      own - there's no "average"

      Last May, I sent an inquiry to Mark Pottenger on behalf of a friend who
      was trying to figure out celestial motions - here's what he wrote about
      precession:

      What is moving in precession is the Earth.

      If Earth was perfectly upright in its orbit, the ecliptic and equator would be the same great circle and the ecliptic pole and the equatorial pole would be the same.

      Since the Earth is tilted from that perfect upright position (currently about 23.5 degrees, varying over time from 22 to 24), the equatorial pole precesses around the ecliptic pole and the equator moves around the ecliptic.

      Stars do not move with respect to the ecliptic except for the very small effect of Proper Motion, which is only significant for the closest stars.

      Mark Pottenger
      ====================
      Love, Diana

    • Arthyr
      Thank you Diana, Are you all right with all that rain? At 10:25 PM 9/1/2006 -0400, you wrote: Fixed star motions answered     Posted by: Arthyr
      Message 2 of 2 , Sep 1, 2006
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        Thank you Diana,

        Are you all right with all that rain?

        At 10:25 PM 9/1/2006 -0400, you wrote:

        Fixed star motions answered

            Posted by: "Arthyr" awc99@... kaldu4you
            Date: Fri Sep 1, 2006 11:11 am (PDT)

        Arthyr sent:

        In my opinion we use precessional motion of one degreee every 72 years. . .
        just looking for confirmation. . .
        ===============================================
        Precession is 0 deg 0 min 50.23 secs a year

        Rule of thumb, 5 minutes of a degree every 6 years

        1 full degree every 71.67 years (72 is fine as an average)

        As for stars' proper motion, it is extremely slow and each star has its
        own - there's no "average"

        Last May, I sent an inquiry to Mark Pottenger on behalf of a friend who
        was trying to figure out celestial motions - here's what he wrote about
        precession:

        What is moving in precession is the Earth.

        If Earth was perfectly upright in its orbit, the ecliptic and equator would be the same great circle and the ecliptic pole and the equatorial pole would be the same.

        Since the Earth is tilted from that perfect upright position (currently about 23.5 degrees, varying over time from 22 to 24), the equatorial pole precesses around the ecliptic pole and the equator moves around the ecliptic.

        Stars do not move with respect to the ecliptic except for the very small effect of Proper Motion, which is only significant for the closest stars.

        Mark Pottenger
        ====================
        Love, Diana

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