🚀 go-pugleaf

"Hugh Williams (London)" wrote:

> Jun 2001 LHR (London, UK)
> Well, I don't understand why the SR times remaining at a certain period
> (from 12/6 to 22/6 ) where it is occurred earlier than the SS times
> indicated (from the period 18/6 to 29/6 ) in the above data.
>

It's due to the fact that the earths orbit about the sun is not perfectly
circular; that apogee (aposol?? I forget) occurs in the northern hemisphere
summer, and therefor the earth is moving slower in its orbit than the yearly
average.  I will leave working out the details as an exercise for the student.

Cheers,
Tim

Tim,

Can you be more specific ? I'll hear from your answer.

Thanks.

Hugh


"Tim Gregg" <timgregg@bestweb.net> ?????
news:3B21A409.85EF72F3@bestweb.net...
>
>
> "Hugh Williams (London)" wrote:
>
> > Jun 2001 LHR (London, UK)
> > Well, I don't understand why the SR times remaining at a certain period
> > (from 12/6 to 22/6 ) where it is occurred earlier than the SS times
> > indicated (from the period 18/6 to 29/6 ) in the above data.
> >
>
> It's due to the fact that the earths orbit about the sun is not perfectly
> circular; that apogee (aposol?? I forget) occurs in the northern
hemisphere
> summer, and therefor the earth is moving slower in its orbit than the
yearly
> average.  I will leave working out the details as an exercise for the
student.
>
> Cheers,
> Tim
>

I was hoping to avoid this since it's far from a simple problem; therefor my
comment about "exercise for the student".

According to Kepplers Laws, a body in orbit about another traces out the same
area per unit time; therefor when it is farther away, near apogee (not the
correct word, apogee is specific to orbits about the earth, but I can't
remember what the correct word is; some help anaybody?) the angle traced out
per unit time is smaller than the average, or what it would be if the orbit
were perfectly circular.  Now, viewed from above in the totally politically
incorrect northern hemishpere-centric view, both the earths rotation and its
orbit about the sun are counter-clockwise.  I will leave it to you to work out
what that would do to the apparent position of the sun in the sky.  Further
complicating the problem, the plane of the earths rotation is set at an angle
of 21� from the plane of the earths orbit, and we are standing on a sphere
approximately halfway up from the equator.  As I said, it's not a simple
problem and would tax practically anybodys powers of visualization.

Possibly for a little help, look for "the equation of time" and discussions of
the corrections which need to be applied to sundials over the course of a year
(that's right, for the same reason that sunrise and sunset times don't progress
evenly, sundials run either fast or slow except for two days a year.)  Good
luck, Mr. Phelps!

"Hugh Williams (London)" wrote:

> Tim,
>
> Can you be more specific ? I'll hear from your answer.
>
> Thanks.
>
> Hugh
>
> "Tim Gregg" <timgregg@bestweb.net> ?????
> news:3B21A409.85EF72F3@bestweb.net...
> >
> >
> > "Hugh Williams (London)" wrote:
> >
> > > Jun 2001 LHR (London, UK)
> > > Well, I don't understand why the SR times remaining at a certain period
> > > (from 12/6 to 22/6 ) where it is occurred earlier than the SS times
> > > indicated (from the period 18/6 to 29/6 ) in the above data.
> > >
> >
> > It's due to the fact that the earths orbit about the sun is not perfectly
> > circular; that apogee (aposol?? I forget) occurs in the northern
> hemisphere
> > summer, and therefor the earth is moving slower in its orbit than the
> yearly
> > average.  I will leave working out the details as an exercise for the
> student.
> >
> > Cheers,
> > Tim
> >