Re: Earth rotation

From: Oriel36 (geraldkelleher_at_hotmail.com)
Date: 07/03/04 

Date: 3 Jul 2004 09:27:06 -0700

"OG" <owen@gwynnefamily.org.uk> wrote in message news:<2km32lF43psfU1@uni-berlin.de>...
> "Oriel36" <geraldkelleher@hotmail.com> wrote in message
> news:273f8e06.0407020906.7545f132@posting.google.com...
> > "OG" <owen@gwynnefamily.org.uk> wrote in message
> news:<2keanvF1dqt2U1@uni-berlin.de>...
> > > "Oriel36" <geraldkelleher@hotmail.com> wrote in message
> > > news:273f8e06.0406260449.6c36d1cd@posting.google.com...
> > > >
> > > >
> > > > 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.
> > >
> >
> > I understand that you did not think the whole thing through carefully
> > enough,not so much that I fault you for it is standard thinking for
> > the last 300 years but I assure you that Equatorial orientation as a
> > property of axial rotation is always tangential to axial orientation.
>
> I said "Equatorial orientation _to the Sun_ does change"
> you say "axial orientation is fixed"
>
> What makes you think that the statements are incompatible. I even emphasised
> the "_to the Sun_" sub clause. How did you miss it?
>
> Do you honestly think that the Sun always has the same orentation relative
> to the Earth's equatorial plane?
> I emphasise the sub-clause "relative to the Earth's equatorial plane"
>
> Do you really think that the sun has the same orientation to the equator
> both Summer and Winter? Really?

The Sun is just a reference for the two seperate motions of the Earth
- axial and orbital.Having two distinct motions will generate two
seperate effects.

Equatorial /axial orientation as a property of axial rotation is
constant insofar as equatorial orientation is always 90 degrees off
the Earth's axis.

http://www.punaridge.org/doc/factoids/Navigation/navfig2.jpg

What causes the change in the seasons is constant axial/equatorial
orientation moving through the change is orbital orientation.

http://www.museum.vic.gov.au/scidiscovery/images/mn000779_w150.gif

The Earth really does have seperate motions - constant axial rotation
and variable orbital motion,the interplay between these two motions
acting in tandem generate the unequal lenght of the day for each axial
rotation wrt to the Sun and the variations in seasons.

If you wish to believe that equatorial orientation to the Sun changes
and causes seasonal change then be my guest but I assure you it is a
property of constant axial/equatorial orientation moving through
variable orbital orientation.

The Sun remains a fixed reference for both axial and orbital motions
and the effects they generate -

 1 - For constant axial rotation moving through the longitudinal
change in orbital orientation,this generates the necessity for the
Equation of Time.

http://www.mhhe.com/physsci/astronomy/fix/student/images/04f15.jpg
 
2 - For constant axial/equatorial orientation moving through the
latitudinal change in orbital orientation,this generates the seasonal
change.

I understand the difficulties of getting your head around treating the
Earth's motions seperately,treating independent axial
motion/orientation as one thing and independent orbital
motion/orientation as another,indeed most websites give into the
temptation of indicating axial tilt to the Sun rather than the
accurate description of axial tilt to the change in orbital
orientation.

http://www.mhhe.com/physsci/astronomy/fix/student/images/04f15.jpg

The astronomers in the 17th century,in their eagerness to reduce
celestial motion to axial longitude coordinates basically wiped out
all reference to orbital motion. The so-called analemma is just
another feature of the celestial sphere or the astronomical step
backwards to an odd mixture or geocentrism and heliocentrism where it
is perceived that the Earth is rotating constantly to what they would
have known as the 'fixed stars'.

http://chemphys.phys.boun.edu.tr/~semiz/universe/near/02ext/star-trails-ex.jpg

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