Re: Earth rotation
From: OG (owen_at_gwynnefamily.org.uk)
Date: 06/29/04
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Date: Wed, 30 Jun 2004 00:02:26 +0100
"Oriel36" <geraldkelleher@hotmail.com> wrote in message
news:273f8e06.0406260449.6c36d1cd@posting.google.com...
>
> My only enemy is laziness rather than anyone in particular.
Don't be too hard on yourself, I don't think you're lazy ;-)
>I will
> freely bring up and discuss the analemmatic images you use to support
> the false contention that constant axial rotation through 360 degrees
> is 23 hours 56 min 04 sec by way of stellar circumpolar motion and
> more importantly,you include axial tilt as a component in the Equation
> of Time.
Err, No I didn't. What I said was that
"The vertical component of the analemma is a consequence of the axial tilt
of the Earth, the lateral component (making it a figure of eight shape) is
therepresentation of the Equation of Time (resulting from the elliptical
orbit)."
Clearly I separated the two components, either you misunderstood me or you
misrepresent me. I'll be generous and assume the former.
> You brought up the analemma and with only a single exception most of
> the websites trade in the same falsehoods.
>
> http://www.longwoodgardens.org/Sundial/Analemma.html
>
> Of particular interest, in that the original use of the analemma only
> refered to the lenght of shadow cast at noon as the Earth rotates to
> face the Sun directly along its axial longitude coordinates,there is
> no figure 8.
>
Well that's natural given the unequal length of the day. When "Noon" was
defined as the sun crossing the meridian, then the only possible variable is
the length of the shadow. As understanding and measurement improved to give
the 'steady-time clock' of sidereal motion, the lateral component of the
analemma (as expressed in the Equation of Time) could be identified.
>
> "Analemma in ancient writers denotes those sort of sun-dials which
> shew only the height of the sun at noon, every day, by the largeness
> of the shadow of the gnomon....If, then, analemma once referred to an
> instrument which focused on the recording of noon time shadows, the
> transition to an instrument which does the same under the "new"
> definition of the time is an easy one to make."
See above - the ancient writers were using the tools available to them. But
they were unable to use tools that were NOT available to them.
> You are bound to consider the motions of the Earth - axial and orbital
> as two distinct and seperate motions.
>
> 1 - The Earth axial rotation and axial/equatorial orientation as a
> distinct and seperate motion
>
> http://ottawa.rasc.ca/pictures/pdelorme/polaris.jpg
>
> That time lapse image taken against the Polaris star tells you that
> axial and equatorial orientation remains constant throughout an annual
> orbit.
Two points
1- this isn't a time lapse image (in the normal meaning of the phrase)
2 - this shows nothing about orientation throughout the annual orbit as it
is a single long exposure (c. 20 minutes by my reckoning). So I fail to see
its relevance.
>The 'Polaris' stellar circumpolar effect is an illusion
> generated by the Earth's axial rotation and insofar as it is useful in
> gauging constant axial/equatorial orientation,it should NOT be used as
> an indicator for equatorial orientation to the Sun.
Who exactly are you telling this to? And why?
> Let's take a look at the analemma image -
> http://www.wengersundial.com/Analemma/analemma.jpg
>
> You are assuming that the Earth's equatorial orientation to the Sun
> changes but as already stated,equatorial orientation is a property of
> the Earth axial orientation as an independent motion which remains
> constant throughout its annual orbit.
Hang on a minute - the Earth's equatorial orientation _to the Sun_ DOES
change
throughout the year. The axial orientation remains the same, but since the
equator is inclined to the ecliptic, the equatorial orientation to the Sun
is bound to change. How strange that you don't see this.
>The Earth does not tilt towards
> and way from the Sun as an independent motion,what occurs is that the
> Earth's ORBITAL orientation changes over the course of an annual
> orbit.
Don't be ridiculous, the orbital plane is constant. That doesn't change. How
could it?
>
> Clearly stated,the Earth's orbital orientation causes the change in
> seasons rather than any property of the Earth's axial tilt which
> maintains constant orientation.
A strange statement. The Earth's orbital orientation has to be in the plane
of the ecliptic (by definition), since the orbit has to be the plane that
cuts the Earth and Sun throughout the year. This does not change over the
year. The effect of which you speak is due to the inclination between the
constant plane of the orbit (which defines the ecliptic and hence the
position of the Sun) and the constant axis of rotation (which defines the
plane of the equator). The difference between the two planes gives rise to
the change in seasons. You can't say that the effect is due to one plane
rather than the other, since it is due to the angle between the two planes.
> > > The Earth's axis remains orientated,over the course of an annual
> > > orbit,to Polaris.
> >
> > Yup!
> >
> > > Now genius,figure this out.
> > >
> > > If axial orientation is constant and the Earth orbits the Sun,you
> > > conclude that it is the change in the daylight/darkness line as a
> > > property of the Earth's orbital orientation which causes the
> > > hemispherical diiference in seasons (summer in Southern/winter in
> > > northern and visa versa).
> >
> > or vice versa
> >
> > > The following graphic will not show you how the daylight/darkness line
> > > as a property of orbital orientation shifts against the Earth's axis
> > > (which remains constantly orientated to Polaris over an annual orbit)
> > > but you will have to assume it.
> > <links snipped>
> > > You will notice that the daylight/darkness line as a property of
> > > orbital orientation changes in accordance with Kepler's second law
> > > subsequently it is this orbital motion of the Earth,assuming constant
> > > axial rotation, that generates the natural unequal day.
> >
> > Agreed - so glad you agree that the sun-at-noon day is unequal
> >
>
> A geometer phrases it as the rotational asymmetry due to constant
> axial rotation moving through variable orbital motion.
Yes, but do you agree that the sun-at-noon day IS unequal?
> > > Axial tilt or equatorial orientation to the Sun changes the asymmetry
> > > between daylight/darkness however it has absolutely no effect on the
> > > total lenght of a day from noon to noon and the Equation of Time
> > > equalises that variation from one rotation to the next.
> >
> > Agreed - the time between the noon and noon on consecutive days is
nothing
> > to do with axial inclination.
> >
>
> Consecutive rotations to be precise,As axial orientation neither
> accelerates or retards the return of axial longitude coordinates back
> to the Sun/Earth line (noon),the variation can only be due to the
> shift in the orbital orientation to the Sun/Earth line.
You keep going on about the earth's axial orientation. This is irrelevant.
> I have spoken of orbital orientation and thought it was clear enough
> but apparently this looks mysterious to some when it clearly is not.
>
> The arrows in the following image reflect the seperate orbital motion
> of the Earth and the division between equal amounts of daylight and
> darkness as a property of the Earth's orbital orientation to the
> Sun.The behavior of the shift in the division between
> daylight/darkness throughout an annual orbit is in accordance with
> Kepler's second law of planetary motion.
> http://www.mhhe.com/physsci/astronomy/fix/student/images/04f15.jpg
>
> http://www.users.muohio.edu/primacag/images/earth%20from%20space.gif
>
> Even without knowing what caused the unequal lenght of a day as
> measured by one axial rotation through 360 degrees wrt the Sun to the
> next,our astronomical ancestors crafted the 24 hour/360 degree
> longitude system to the assumption that axial rotation is constant via
> the Equation of Time correction.
Unless you have a constant clock, you don't know about the Equation of Time.
The Sun does not provide a constant clock. Therefore the 'astronomical
ancestors' did not have the EoT.
>In the 21st century we can see that it
> is not only the effect of constant axial rotation moving through
> variable orbital motion,but how the orbital orientation changes in
> accordance with Kepler'ssecond law.
>
> > > The analemma or basically what the geocentric motions of the Sun look
> > > like from the perspective of a 24 hour clock is astronomical fraud
> >
> > What do you mean when you say it is a fraud?
> >
>
> Ah,Flamsteed !.
>
> As axial rotation was already assumed to be constant by way of the 24
> hour/360 degrees longitude equivalency and the Equation of Time
> correction,Flamsteed creates a fraud by piggybacking on that existing
> assumption and linking the Earth's rotation directly to stellar
> circumpolar motion.
Let me see, IIUY, you don't claim there is an equable solar clock. However,
you do claim that if the uneven Solar clock is 'corrected' by the Equation
of Time then there is a constant clock. Is this what you mean?
If we can clarify this point then we can continue this thread.
<rest of thread snipped, but I may return to it later>
Just one little question though - did you do the experiment with Cartes de
Ciel?
- Next message: Jack Sarfatti: "Surprising apriori Bohmian HV calculation of 10^-17 cm weak force scale"
- Previous message: Chris L Peterson: "Re: Night Sky Brightness at Sites from DMSP-OLS Satellite Measurements"
- In reply to: Oriel36: "Re: Earth rotation"
- Next in thread: Jonathan Silverlight: "Re: Earth rotation"
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