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Old April 25th 08, 04:12 PM posted to uk.sci.astronomy
oriel36[_2_]
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Posts: 8,478
Default Equation of Time

On Apr 25, 12:47*pm, Les Desser wrote:
I am preparing a presentation on the Equation of Time and have been
trying to find a clear description, preferable with diagrams, of the
adjustment due to obliquity.

The explanation at the National Maritime Museum
http://www.nmm.ac.uk/server/show/conWebDoc.351 only makes sense if you
already know the answer

The best I could find was the page at
http://www.wallingfordclock.talktalk.net/Sidereal%20Time.htm but I
still find it inadequate.

The example of the bus going down the incline is good to show the
slowdown but I cannot find anything appropriate to explain the speeding
up.

Has anyone seen and better presented explanations?
--
Les Desser
(The Reply-to address IS valid)


There is only one accurate explanation of the Equation of Time in
existence and even that is incomplete -

http://www.xs4all.nl/~adcs/Huygens/06/kort-E.html


The Equation of Time creates the 24 hour day out of the natural noon
cycle -

"the Earth...makes an entire revolution in the Ecliptick in 365 days,
5 hours 49 min. or there about, and that those days, reckon'd from
noon to noon, are of different lenghts; as is known to all that are
vers'd in Astronomy. Now between the longest and the shortest of those
days, a day may be taken of such a length, as 365 such days, 5. hours
&c. (the same numbers as before) make up, or are equall to that
revolution: And this is call'd the Equal or Mean day, according to
which the Watches are to be set; and therefore the Hour or Minute
shew'd by the Watches, though they be perfectly Iust and equal, must
needs differ almost continually from those that are shew'd by the
Sun,..But this Difference is regular, and is otherwise call'd the
Aequation," Huygens

The Equation of Time also keeps one of these 24 hour days elapsing
into the next 24 hour day,Monday into Tuesday ect.

When Copernicus discovered that the orbital motion of the Earth around
the central Sun accounted for the observed behavior of the other
planets,it left axial rotation to explain the daily cycle.When axial
rotation was discovered,the timekeeping astronomers applied the
Equation of Time (EOT) principles to terrestrial geometry and
geography,they did not have to assume axial rotation to be constant
but as the EOT facility which keeps the 24 hour day to natural
noon,they exploited this principle which allows axial rotation to be
considered constant as a convenience and not as an observation.It is
tricky the way it all works but the actual astronomical means is
nothing like the fiction of the NMM treatment.

It is absolutely crucial to understand what the Equation of Time
actually represents in terms of axial and orbital
motions,provisionally,it represents a rate of change using natural
noon as a benchmark without going into further details.

Of course most here do not recognise variations in the difference
between natural noon and 24 hour clock noon as the irreducable
complexity of the solar/sidereal fiction requires noon cycles to be
equal,the distance the Earth travels in its orbit must correspond
to .986 degrees/3 min 56 sec in order to conclude that the Earth
rotates through 360 degrees in 23 hours 56 minutes 04 seconds -

http://en.wikipedia.org/wiki/Image:T...3%A9reo.en.png

If you can explain the Equation of Time with the graphic above then
good for you,the fact that it is pure fiction hardly matters to those
who will comfortably give you advice in regards to the Equation of
Time yet still believe the Earth rotates through 360 degrees in 23
hours 56 minutes 04 seconds.Think of it as Piltdown man to the power
of 100 when you get your replies.