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  1. #21
    acridiniumester@googlemail.com's Avatar
    acridiniumester@googlemail.com Guest

    Default Shadow of sundial a straight line on equinox day?



    On 31 Mar, 21:49, oriel36 <kelleher.ger...@gmail.com> wrote:
    If you want to do this properly buy a globe of the Earth with the
    correct axial tilt. Put a light or a candle in the centre of a table.
    Point the north pole of the globe at your point representing Polaris
    and, maintaiing this orientation move the globe round the candle. You
    will note that you don't have to have any complicated extra orbital
    motion to explain the seasons since it will be obvious that the Earth
    rotates about it's tilted (with respect to the orbital plane) axis
    which maintains its orientation with Polaris - or to put it another
    way the "Celestial Sphere".
    If you can't understand this there is something wrong with your brain

  2. #22
    starman's Avatar
    starman Guest

    Default Shadow of sundial a straight line on equinox day?

    oriel36 wrote:

    Wow, it looks like you have finally been able to explain it in a way
    that most everyone else here has understood all along. Now the big
    question for you is, do you know why the rotational axis of the earth
    (broomstick) remains fixed to the same distant point in space while the
    earth orbits the sun? I have a feeling this is going to open a whole new
    can of worms.

  3. #23
    canopus56@yahoo.com's Avatar
    canopus56@yahoo.com Guest

    Default Shadow of sundial a straight line on equinox day?

    On Mar 28, 7:19 pm, br...@lunabase.org (Brian Tung) wrote:

    Thanks for the correction, Brian. I meant to say hyperbola and not
    parabola. - Kurt

  4. #24
    canopus56@yahoo.com's Avatar
    canopus56@yahoo.com Guest

    Default Shadow of sundial a straight line on equinox day?

    On Mar 30, 7:30 am, Peter Lewis <kingkon...@gmail.com> wrote:

    A basketball with markers taped to the poles and a flashlight at more
    than 10 meters works.

    There the NASA JPL Space Simulator may be of help:

    http://space.jpl.nasa.gov/

    For 2009, the equinoxes and solstices are at:

    2009
    Equinoxes Mar 20 11 44 Sept 22 21 18
    Solstices June 21 05 45 Dec 21 17 47

    Use March 20, 2009 at 11:44 UT in the simulator. Look at the Earth
    from above and from "The Sun". Compare the position of the Earth as
    seen from the Sun. The Sun will appear to be directly over the
    equator. http://en.wikipedia.org/wiki/Equator

    Because the Sun has no visual parallax when viewed from the Earth, the
    rays of the Sun appear to be parallel, no matter whether you are look
    at the Sun from a high latitude or from the equator. That's why the
    Sun traces a visual straight line for all gnonoms.

    Try running the simulator at other times of the year. You'll see that
    the Sun does not appear to be directly over the equator. That's when
    the Sun's shadow traces a hyperbola. Think in terms of conics - a
    plane intersecting a sphere.

    - Kurt

  5. #25
    dkelvey@hotmail.com's Avatar
    dkelvey@hotmail.com Guest

    Default Shadow of sundial a straight line on equinox day?

    On Mar 31, 7:02 am, Peter Lewis <kingkon...@gmail.com> wrote:

    Hi
    I thought I might add a little here. At the equinox, the suns shadow
    would
    follow the line of latitude where the person is located. For most any
    location
    that wasn't near the poles, this would seem to be a straight line,
    although,
    as drawn on the suface of the earth, it would curve, as all latitude
    lines
    do. If one had a truly flat board, not one that followed the Earth
    curvature,
    it would cast a straight line.
    Dwight

  6. #26
    palsing's Avatar
    palsing Guest

    Default Shadow of sundial a straight line on equinox day?

    On Mar 28, 11:50 pm, oriel36 <kelleher.ger...@gmail.com> wrote


    What a monstrous ego you have, to state that not one of the great
    scientific minds of these times understands the basic dynamics of the
    seasons, whereas you yourself know them perfectly. You are simply
    delusional.

    You are certainly correct when you lament the fact that it will be
    more difficult than you thought to find even one person who thinks the
    way you do...

  7. #27
    starman's Avatar
    starman Guest

    Default Shadow of sundial a straight line on equinox day?

    oriel36 wrote:


    It is you who does not understand the *fundamental* cause of the seasons
    if you can not explain why the earth's rotational axis remains fixed in
    space towards the star Polaris while it (the earth) orbits the sun. If
    you don't know the answer, it shouldn't take you more than a minute or
    two to Google it. But of course the 'real' astronomers all ready know
    the answer without having to look it up.

  8. #28
    starman's Avatar
    starman Guest

    Default Shadow of sundial a straight line on equinox day?

    Golden California Girls wrote:


    I don't have to look it up. I've known about both of those phenomena
    since I was a teenager. I didn't want to add more confusion to his
    existent confusion. One step at a time.

    Whoops, I'm feeding another troll.

  9. #29
    starman's Avatar
    starman Guest

    Default Shadow of sundial a straight line on equinox day?

    > On Apr 1, 8:16 pm, starman <star...@bluesky.net> wrote:

    Let's forget about the global warming issue until you first give a
    satisfactory answer to the pending question in this thread. You are
    basing your understanding of the relationship between the inclination
    (tilt) of the earth's rotational axis in relation to it's orbital plane
    (around the sun), on imaging and other observations, which is fine.
    However I'm asking you to explain the underlying principle of physics
    which causes the observed behavior of the planets such as Uranus, which
    you like to use as an example. Specifically, why does the earth's
    rotational axis remain fixed to the same point in space, like your
    broomstick analogy, while the earth orbits the sun? Or to put the
    question in the negative, why *doesn't* the axis of the earth's rotation
    always point *towards* the sun during it's annual orbit? If this were
    true, it would be like the broomstick always pointing towards the basket
    in the center of the room while the student walks around it. I think you
    will agree that this is not the case but why? It might be helpful if you
    do some research on a child's toy which is often used as an
    instructional aid in a high school physics class. Hint: The name begins
    with the letter 'G'.

  10. #30
    starman's Avatar
    starman Guest

    Default Shadow of sundial a straight line on equinox day?

    oriel36 wrote:


    My only intention was to get you to do a little research to discover the
    name and principles of the device or educational tool starting with the
    letter 'G' which explains why the rotational axis of the earth remains
    fixed to the same location in space, like your broomstick does in the
    room. Haven't you ever wondered why this is so? I guess you made no
    attempt to do that research. All I'm asking for is the name of that
    device. If you can not provide it, you do not truly understand the
    underlying physical principles which govern the behavior of any rotating
    body, whether it be a planet or just a child's toy top. I imagine there
    are more than a few readers here who are waiting to see if you can do
    it. No spoilers please.
    Last chance, what's the word?

 

 
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