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  •  I'm confused. (1+ / 0-)
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    maizenblue

    If a planet is rotating at a declination(?) of 45% from ours, won't it - as a sphere - occlude its star just as much as if it were 'straight on'?

    Ignorance isn't exactly bliss but some things are better known when they are unknown to start with and pieced together on the way. - WineRev

    by Clem Yeobright on Sun Mar 08, 2009 at 06:39:05 AM PDT

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    •  Hmmm (1+ / 0-)
      Recommended by:
      Clem Yeobright

      not sure what you're asking. For the planet to trnasit the star from our/Kepler's view, the ecliptic only has to cross in front or nearly in front of that star. But that alien ecliptic can be all cock-eyed compared to ours. It could be at right angles or any angle in between to our local ecliptic.

      Read UTI, your free thought forum

      by DarkSyde on Sun Mar 08, 2009 at 06:41:38 AM PDT

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      •  Our eliptic (1+ / 0-)
        Recommended by:
        Clem Yeobright

        was, in the 1960's, explained incorrectly to me in school.

        Early models of our solar system showed the earth "tilting" on its axis every six months, instead of the off center orbit we know to be true.

        If the earth tilted every six months, everything not deeply rooted to the ground would be flung off into space.

        Were we taught a "simplistic" version of our actual orbit for the sake of building a gizmo that had a perpendicular plane, or was it a widespread belief fifty years ago?

        Nothing can now be believed which is seen in a newspaper. Truth itself becomes suspicious by being put into that polluted vehicle. Thomas Jefferson 6/11/1807

        by Patriot4peace on Sun Mar 08, 2009 at 06:47:58 AM PDT

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        •  It was a simplistic explanation (0+ / 0-)

          Earth as a gyrocompass, always pointing (well, over human lifespans) in the same direction as it revolved around the sun, has been understood since the heliocentric model was developed.

          What I think might have happened in some cases is that when this is explained, they use a model globe.  To show the different orientations of the Earth at different times of the year, it's often easier to turn the globe around (thus changing the rotational axis) then it is to change its position relative to the light source which is what really happens.  It can give people the idea the planet is flopping around.

        •  crystal spheres (0+ / 0-)

          For most practical purposes our current model has been fixed since Newton, over 300 years ago. The problem you are talking about, which is that the spinning axis of the Earth would change orientations if the Earth were attached to the Sun by a rigid connection (like the old crystal spheres) came up briefly in the Copernican model before Kepler's work did away with the crustal spheres. It's  called the problem of the 'second and third' motions, and discussed by Kuhn. It's not known whether it bothered Aristarchus, who came up with the same model as Copernicus in about 250 BC.

          I wish we could say nobody teaches such crap anymore.

          •  It really began to bother me (0+ / 0-)

            in Physics class ten years later - when I realized that a trillion tons of planet could not suddenly change direction without losing all of the inhabitants.

            Nothing can now be believed which is seen in a newspaper. Truth itself becomes suspicious by being put into that polluted vehicle. Thomas Jefferson 6/11/1807

            by Patriot4peace on Sun Mar 08, 2009 at 09:11:59 AM PDT

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      •  Didn't mean rotate, of course: 'revolve' (1+ / 0-)
        Recommended by:
        DarkSyde

        But if the planet occludes/transits the star from our perspective (which is every case except the extreme), doesn't it prove its presence equally as well? Or, is there something 'special' about the equator of the star (from our perspective) that transit at or near that 'level' produces a different profile?

        Ignorance isn't exactly bliss but some things are better known when they are unknown to start with and pieced together on the way. - WineRev

        by Clem Yeobright on Sun Mar 08, 2009 at 06:56:45 AM PDT

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        •  If (1+ / 0-)
          Recommended by:
          Clem Yeobright

          the exoplanet orbits its star outside the plane of that star's equator, no matter how far out of the plane it may be, and still crosses in front of the star, yes, Kepler would potentially be able to detect the transit just like any other. In fact, my guess is we would simply infer that's where the plane of the star's equator was, becuase I don't think there's  any other way to tell with present technology anyway, and our theories and observations of existing protoplanetary disks, are disks, precisely because they accrue in a plane at right angles to the star's spin axis. It's an interesting side question as to how much a star's obliquity can change over time afterward. Just off the top of my head, my guess would be the larger the total mass of orbiting planets, the more 'locked in' a star would be to a smaller range of obliquity, but that math sounds fiendish to work out in detail.

          Read UTI, your free thought forum

          by DarkSyde on Sun Mar 08, 2009 at 07:03:34 AM PDT

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          •  one can tell whether (2+ / 0-)
            Recommended by:
            DarkSyde, Clem Yeobright

            an exoplanet orbits in a plane that is
            inclined to the equator of the star if the exoplanet also transits the star. This is
            called the Rossiter-McLaughlin effect and Greg Laughlin explains this nicely at
            oklo.org with respect to weird exoplanet around HD 80606

            H.L. Mencken: "A nation of sheep begets a government of wolves"

            by igneous on Sun Mar 08, 2009 at 07:36:52 AM PDT

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            •  "Equator of the star" (0+ / 0-)

              You are referring, I think, to the equator from our (Kepler's) perspective, NOT the equator defined by the rotation of the body, right?

              I'm still disoriented (can't find that damned East - it was here a minute ago, dammit!)

              1. Is the (apparent) brightness of a star distributed evenly across the disk or does the radiation proceed from within the star and is it therefore directional, so that an area near the (apparent) pole contributes less than does an equal area on the (apparent) equator to the light Kepler captures?
              1. Does a planet with a particular period whose orbit is - from our perspective - offset spend less time in its (apparent) transit than one with the same period that appears to follow the equator? I have to guess yes, since a planet offset by 90 degrees from us will appear to transit not at all, in zero time, one might say, and zero is a quite different value than any other.... [Never mind, I think I've resolved this one.]
              1. Does the effect you describe relate to the relationship of the transit time to the period?

              Thanks!

              Ignorance isn't exactly bliss but some things are better known when they are unknown to start with and pieced together on the way. - WineRev

              by Clem Yeobright on Sun Mar 08, 2009 at 08:53:48 AM PDT

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              •  How does this work? (0+ / 0-)

                An exoplanet (as an inner planet in our system) spends its time - from our perspective - in three states: occluding the star, occluded by the star, and neither occluding nor occluded. Mercury spends much less time in the third state than does Venus, because of Mercury's closer orbit.

                So the key to size and mass would be to determine how much time is spent in each state, and multiple observations permit the estimate of orbit size, no?

                Ignorance isn't exactly bliss but some things are better known when they are unknown to start with and pieced together on the way. - WineRev

                by Clem Yeobright on Sun Mar 08, 2009 at 09:04:53 AM PDT

                [ Parent ]

            •  If (1+ / 0-)
              Recommended by:
              Clem Yeobright

              a star did indeed roll its spin axis significanty after a planet's accretion, might the tidal effects then induced account for orbital migration inferred for some hot jupiters orbting their sun well inside the relative orbit of mercury?

              Read UTI, your free thought forum

              by DarkSyde on Sun Mar 08, 2009 at 08:59:16 AM PDT

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