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  1. #1
    Aditya Naredi's Avatar
    Aditya Naredi Guest

    Default measured difference in azimuth of Sun?



    Hi everyone,

    A few days back I heard from my hometown in India that people
    observed a 'northern shift' of Sun during sunrise. This happened
    around July 17th (2003). Unbelievable as it seemed, I proceeded to
    measure it myself as follows..

    I calculated the angle the shadow of a vertical body made with
    True North (determined by a compass) at different times and
    different places in Seattle (USA). I compared this angle
    (that Sun makes from true north - called 'azimuth') with the
    calculated angles posted on numerous official and unofficial
    websites, and I found it differing exactly by 15 degrees.

    Here are the results:

    Data:
    Magnetic declination in Seattle (19 degrees East)
    Place Seattle, WA USA (122 20 W, 47 38 N)
    Calculated data taken from the website: http://aa.usno.navy.mil/data/
    (US Navy?)

    I was careful the measurements were taken in a magnetic influence
    free environment.

    Date Time Measured Calculated Difference
    (with True North) (from website)
    ----------------------------------------------------------------
    07/29/03 15:30PM 235 degrees 250 degrees 15 degrees
    07/30/03 10:46AM 124 degrees 140 degrees 16 degrees
    08/01/03 16:40PM 250 degrees 264 degrees 14 degrees


    Obviously the first thing that comes to my mind is that the
    calculations are wrong (wrong caliberation of compass etc), or direction
    of Magnetic Pole changed here in Seattle - but since the same difference
    has been observed in other places too, I don't think that's the
    case.

    Can someone please measure Sun's azimuth at their places and let me
    know if it differs from calculated azimuth or not? If it is, what are
    the possible explanations? If not, what am I doing wrong?

    If these observations are correct, it would be interesting to measure
    measure altitude / azimuth of Polaris. I don't have any instruments
    to do that right now - am working on it.

    Would really appreciate your help.

    Thanks in advance,
    Aditya

  2. #2
    Thomas McDonald's Avatar
    Thomas McDonald Guest

    Default measured difference in azimuth of Sun?


    "Aditya Naredi" <advik@anahada.com> wrote in message
    news:d88c89f2.0308011602.14874e34@posting.google.c om...

    Aditya,

    I think you might call a local observatory or active amateur astronomer
    and ask them if their telescope pointing software is laying their telescopes
    on target.

    If you have a telescope (lowest possible power) or binoculars on a
    relatively steady mount, you can aim it at Polaris and lock it down very
    well. Check it frequently. If Polaris stays in the field of view, the
    world has not tilted. (Remember that Polaris is off-set from true north by
    not quite a degree; some shift in postion might be noticed; but if things
    are as bad as you and your friends in India fear, Polaris would move out of
    the field of view pretty quickly.)

    If you don't have a 'scope, you could fix a long straight-edge to a
    sturdy vertical surface (tree, post, etc.) aimed directly at Polaris. This
    would accomplish the same thing as above.

    You will find that the sky has not, in fact fallen; and that you and
    your friends have made an elementary mistake somewhere.

    Tom McDonald



  3. #3
    Odysseus's Avatar
    Odysseus Guest

    Default measured difference in azimuth of Sun?

    Aditya Naredi wrote:
    [snip]
    The first thing I'd suspect is that the sunrise positions you looked
    up were just the "geometrical" azimuths. Atmospheric refraction and
    other effects not included in such figures can make a very large
    difference to the observed position. Moreover, I imagine that looking
    north-east from Seattle the horizon is pretty mountainous; you might
    do better trying to observe sunsets over the Juan de Fuca Strait.

    --
    Odysseus

  4. #4
    Aditya Naredi's Avatar
    Aditya Naredi Guest

    Default measured difference in azimuth of Sun?

    Thanks for your followups. Please see my comments inlined:

    "dlzc@aol.com \(formerly\)" <dlzc1.cox@net> wrote:

    I know about that, I adjusted 19 degrees for Seattle's magnetic declination to
    get true north from magnetic north.

    Thomas McDonald" <tsmac@wwt.net> wrote

    would definitely try that.

    Odysseus <odysseus1479-at@yahoo-dot.ca> wrote in message

    well, I measured this at different times of the day so its not always sunrise.
    Atmospheric refraction shouldn't affect this at noon (even if it does in small
    degrees, it would affect altitude, not azimuth). This also means that I'm not
    always looking north-east from Seattle (actually its south-west in afternoon).

    Guys I really appreciate your responses. But did any of you actually try to
    measure it yourself? I'm 100% sure, you'll notice this difference too. Could
    you please? That's just 5 minutes out in the Sun!

    Thanks,
    Aditya.

  5. #5
    Paul Schlyter's Avatar
    Paul Schlyter Guest

    Default measured difference in azimuth of Sun?

    In article <d88c89f2.0308011602.14874e34@posting.google.com >,
    Aditya Naredi <advik@anahada.com> wrote:


    Since your discrepancies are very near 15 degrees, I strongly suspect
    an error of precisely 1 hour in time in your computed values. Perhaps
    you forgot to account for Daylight Savings Time? Or perhaps you used
    the wrong time zone? It's hard to tell which, since you don't give enough
    details about your computations.


    I can assure you that Polaris has not shifted azimuth by 15 degrees.
    My country house (where I am right now) is oriented precisely
    in the north-south direction (within a degree or better), and Polaris
    was at its usual direction in the sky last night relative to that
    house. I would immediately have noticed a shift of 15 degrees....

    Also, my sundial in the garden shows correct solar time still. It
    would have been one hour off if there had been a 15 degree shift in
    solar azimuth.

    Finally, a 15-degree shift in solar azimuth would also put the narrow
    zones of total and annular solar eclipses on the Earth's surface 15
    degree off their predicted values, making expeditions to these solar
    eclipses miss their targets -- and that would be BIG NEWS !!!!!

    --
    ----------------------------------------------------------------
    Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
    e-mail: pausch at stockholm dot bostream dot se
    WWW: http://www.stjarnhimlen.se/
    http://home.tiscali.se/pausch/

  6. #6
    Paul Schlyter's Avatar
    Paul Schlyter Guest

    Default measured difference in azimuth of Sun?

    In article <3F2B1DFC.489E5BC1@yahoo-dot.ca>,
    Odysseus <odysseus1479-at@yahoo-dot.ca> wrote:


    He didn't measure this at sunrise - check his data:

    # Data:
    # Magnetic declination in Seattle (19 degrees East)
    # Place Seattle, WA USA (122 20 W, 47 38 N)
    # Calculated data taken from the website: http://aa.usno.navy.mil/data/
    # (US Navy?)
    #
    # I was careful the measurements were taken in a magnetic influence
    # free environment.
    #
    # Date Time Measured Calculated Difference
    # (with True North) (from website)
    # ----------------------------------------------------------------
    # 07/29/03 15:30PM 235 degrees 250 degrees 15 degrees
    # 07/30/03 10:46AM 124 degrees 140 degrees 16 degrees
    # 08/01/03 16:40PM 250 degrees 264 degrees 14 degrees

    The Sun doesn't rise, or set, at 15:30PM, 16:40PM or 10:46AM in July
    at 47 deg N latitude....

    Since his discrepancies are all near 15 degrees, my first guess is
    that he made a "one hour mistake": either forgetting to account
    for Daylight Savings Time, or by mistake choosing the wrong time zone.

    --
    ----------------------------------------------------------------
    Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
    e-mail: pausch at stockholm dot bostream dot se
    WWW: http://www.stjarnhimlen.se/
    http://home.tiscali.se/pausch/

  7. #7
    John Oliver's Avatar
    John Oliver Guest

    Default measured difference in azimuth of Sun?

    Aditya Naredi wrote:

    Go back and look at the Naval Observatory tabulations ... they are
    for Pacific Standard Time, not Pacific Daylight Time ... using
    those tables
    Date PDT Your measure PST USNO Diff (O-c)
    07/29/03 15:30PM 235 degrees 14:30PM 235 deg 0 deg
    07/30/03 10:46AM 124 degrees 09:46AM 121 deg 3 deg
    08/01/03 16:40PM 250 degrees 15:40PM 253 deg -3 deg

    Looks pretty normal to me.


  8. #8
    Aditya Naredi's Avatar
    Aditya Naredi Guest

    Default measured difference in azimuth of Sun?

    pausch@saaf.se (Paul Schlyter) wrote in message news:<bgfro9> >

    you are right, the websites I looked at used PST - not accounting for daylight
    saving time. That explains it.

    Thanks a lot for your help,
    Aditya.

  9. #9
    Odysseus's Avatar
    Odysseus Guest

    Default measured difference in azimuth of Sun?

    Aditya Naredi wrote:
    Sorry, I didn't read your table carefully enough.

    --
    Odysseus

  10. #10
    bwhiting's Avatar
    bwhiting Guest

    Default measured difference in azimuth of Sun?

    Plus, I would think, common sense wise, that if the
    sun had shifted its position in our sky (which means
    a shift in the earth) the Big Boys out at Kitt peak,
    et al...who track the sun all the time, plus the solar
    satellites, something of that nature would have made
    world-wide headlines...by now.
    FWIW,
    Tom W.


 

 

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