Twilight lengths at different latitudes

On Tue, 9 Oct 2012 17:25:00 -0700 (PDT), Quadibloc
wrote:
That is absolutely right, since the zone of twilight is clearly X
miles wide at the terminator, no matter what your latitude is, ....

....assuming a spherical Earth. On the real Earth, there are small
dependencies of latitude and of solar declination.

On Oct 10, 8:20*am, Martin Brown
wrote:
On 09/10/2012 20:09, oriel36 wrote:









On Oct 9, 5:26 pm, palsing wrote:
On Monday, October 8, 2012 9:54:58 PM UTC-7, oriel36 wrote:
The easiest of all insights to understand is why twilight lengths

diminish towards equatorial latitudes,the obvious reason being that

faster surface speeds passing through the circle of illumination cause

a rapid transition from daylight to darkness at the equator and the

transition becomes longer as the speeds diminish towards the polar

latitudes.

The polar twilight around the equinox is a separate issue as its cause

arises from the orbital behavior of the Earth carrying the polar

coordinate through the circle of illumination at a vastly slower rate

and contemporaries make themselves look ridiculous by appealing to a

'Sun angle' rather than looking at twilight in its daily and separate

seasonal formats.

The nuisance Ra/Dec observers appeal to a blatantly stupid explanation

that doesn't dignify a response as it is the usual stellar circumpolar

celestial sphere and the Sun hitting the horizon at a different angle

whereas common sense *determines surface rotational speeds are the

cause -

http://curious.astro.cornell.edu/que...php?number=121

So,with so many world travelers who can now move quickly from place to

place and who notice the pronounced difference in twilight lengths,it

is time to act like adults and give them a proper explanation using

the daily motion of the planet.

It is just not that simple...

http://www.gandraxa.com/length_of_day.xml

Twilight lengths are the easiest way to understand that the Earth is
round and rotating and in broad brushstrokes - latitudinal speeds
correlate with twilight lengths,the faster the surface speed the
quicker the transition from daylight to darkness as a meridian passes
through the circle of illumination.Of course it takes an astronomer to
convert one rotation in one 24 hour day into the details of 15 degrees
of rotation per hour equating to 1037.5 miles per hour at the equator
hence the shortest twilight occurs at the equator and lengthens as the
rotational speeds diminish towards the poles .

It has absolutely nothing whatsoever to do with puny Ra/Dec ideologies
of 'Sun angles' hitting the horizon .

So,here is an insight that needs processing and later investigations
will come the polar twilight where the polar coordinates act like a
beacon for the orbital behavior of the Earth and especially at the
equinoxes as those coordinates turn through the circle of illumination
in being carried through it by the orbital behavior of the Earth.

I don't expect *many readers of grasping the latter insight presently
but the rotational speeds and twilight lengths as an insight is within
the comprehension of teenagers so the lack of a clear explanation
using surface speeds makes it fairly obvious that there is a lot of
welfare fraud going on out there at the expense of students and the
wider population.

Again,this is a new way to approach twilight lengths in an era of
rapid *travel between latitudes where the experience is fairly
dramatic for people traveling from fairly high latitudes to equatorial
latitudes.There is no process to work this explanation into mainstream
viewing for obvious reasons so the difficulty is not technical as the
explanation is *correct,the difficulty is the lack of a valid
astronomical *institution that can transmit the observation - nothing
more and nothing less.

The length of twilight correlates even better with the altitude of the
sun at local noon transit. You are thicker than two short planks.

--
Regards,
Martin Brown

I assure you,when you travel at 1037.5 miles per hour through the
circle of illumination at the equator as opposed to slower latitudinal
speeds towards the polar coordinates, the effect is a fairly rapid
transition from daylight to darkness but the issue is not convincing
people who can't be convinced but rather pointing out that there is no
process by which this accurate explanation moves from Usenet to
mainstream education,not even this simple correlation.

It is not possible to bundle daily twilight with polar twilight that
occurs at the equinoxes as the causes are separate insofar as the
polar coordinates swing through the circle of illumination due to the
orbital behavior of the planet.Despite appearances,what looks quite
simple rapidly becomes complex and vibrant with a multitude of
different effects and causes making themselves known.

Chant Ra/Dec voodoo all you like,the cause is common sense and
although it does not appeal to empirical welfare cheats who never met
an astronomical insight they didn't destroy or distort,these people
matter little now.'Celestial mechanics' indeed,a lovely little insight
like this one and we have professors here unable to grasp the details
of a round and rotating planet and the local cause of twilight at the
circle of illumination !.

On Tuesday, October 9, 2012 11:34:19 PM UTC-7, oriel36 wrote:


It is a fact that latitudinal surface speeds correlate to twilight

lengths and prove that the Earth is round and rotating with a maximum

speed of 1037.5 miles per hour.

No, that is not a fact at all. The ONLY fact that is relevant is that astronomical twilight is not achieved until the sun is 18 degrees below the horizon, from wherever you happen to be on the surface of the earth, as per its definition.


The ridiculous Ra/Dec explanation using 'Sun angle' descent is from a

community with a lack of sense of solar system scale as individual

objects or the distances between them -

The definition of twilight never mentions the RA/DEC system, which has nothing whatsoever to do with twilight. Astronomical twilight isn't over until the sun is 18 degrees down, pure and simple.


Behind the simple explanation of twilight length using surface speeds

is the orbital twilight at the polar coordinates around the equinoxes

as they are carried around in a circle to the central Sun and why the

old perception of axial precession must be dismissed and move to a

long term orbital trait -



http://en.wikipedia.org/w/index.php?...ion.svg&page=1


Axial precession is only important on a very long 26,000 year scale and never belongs in any conversation about the length of twilight... once again you have used a link that is totally inappropriate as an illustration for the point you are trying to make.


I told you before,the natural tendency of the empiricist is to move

technical details,even simple one like these,into personal insults

becomes a waste of time and energy and you may again get the luxury of

saying whatever you wish without a response from me.

The fact is that you have never actually responded to me. You don't actually answer any questions asked of you. I (we) present facts, you present "intuitive interpretation".

You have repeatedly said that the return of a star does not correspond to the rotation of the Earth, and therefore you have been repeatedly asked what the return of a star means to you, but so far you have never answered this simple and direct question. Why not?

Finally, as per the dictionary, it is YOU who is the empiricist...

em·pir·i·cism (m-pîr-szm)
n.

On Oct 10, 4:46*am, Paul Schlyter wrote:
On Tue, 9 Oct 2012 17:25:00 -0700 (PDT), Quadibloc
wrote:

That is absolutely right, since the zone of twilight is clearly X
miles wide at the terminator, no matter what your latitude is, ....

...assuming a spherical Earth. On the real Earth, there are small
dependencies of latitude and of solar declination.

True. But at least the Earth comes closer to being spherical than a
cow.

John Savard

That is much better

On Oct 10, 5:22*pm, palsing wrote:
On Tuesday, October 9, 2012 11:34:19 PM UTC-7, oriel36 wrote:
It is a fact that *latitudinal surface speeds correlate to twilight

lengths and prove that the Earth is round and rotating with a maximum

speed of 1037.5 miles per hour.

No, that is not a fact at all. The ONLY fact that is relevant is that astronomical twilight is not achieved until the sun is 18 degrees below the horizon, from wherever you happen to be on the surface of the earth, as per its definition.


You are drawing attention to an issue as old as astronomy itself and I
have come to understand what distinguishes you from the geocentric
astronomers who looked out into the celestial arena and made sense of
motions in relation to each other and to the Earth whereas Ra/Dec
observers cannot make the distinction and work off a rotating
celestial sphere with above and below as working principles,something
the geocentric astronomers had long since set aside.

" “And, finally, in what sense, and in reference to what thing is
Earth said to be ‘intermediate?’ For the universe is infinite; now
that which is infinite hath neither beginning nor limit, so it does
not belong to it to possess a middle: for infinity is the deprivation
of limits. But he who makes out Earth to be the middle not of the
universe, but of the world, is ridiculous for his simplicity if he
does not reflect that the ‘world’ itself is liable to the very same
objections: for the universe hath not left a middle place for it also,
but it is borne along without house or home in the boundless vacuum,
towards nothing cognate to itself; perhaps it has found out for itself
some other cause for remaining fixed, and so has stood still, but
certainly not owing to the nature of its position. And it is allowable
for one to conjecture alike with respect to Earth and with respect to
the moon, that by some contrary soul and nature they are [actuated,
the consequence of the diversity being] differences, the former
remaining stationary here, the latter moving along. But apart from
these considerations, see whether a certain important fact has not
escaped their notice. For if whatsoever space, and whatever thing
exists away from the center of Earth, is the ‘above,’ then no part of
Earth is ‘below,’ but Earth herself and the things upon Earth; and, in
a word, everybody standing around or investing the center, become the
‘above;’ whilst ‘below’ is one sole thing, that incorporeal point,
which has the duty of counterbalancing the whole constitution of the
world; if, indeed, the ‘below’ is by its nature opposed to the
‘above.’ And this is not the only absurdity in the argument, but it
also does away with the cause through which all ponderous bodies
gravitate in this direction, and tend downwards: for there is no mark
below towards which they move: for the incorporeal point is not likely
(nor do they pretend it is) to exert so much force as to draw down all
objects to itself, and keep them together around itself. But yet, it
is proved unreasonable, and repugnant to facts, to suppose the ‘above’
of the world to be a whole, but the ‘below’ an incorporeal and
indefinite limit: whereas that course is consistent with reason, to
say, as we do, that the space is large and possessed of width, and is
defined by the ‘above’ and the ‘below’ of locality."

http://thriceholy.net/Texts/Moon.html

In short,the degrees of the Sun below the horizon in other to define
different versions of twilight is quaint but really unproductive and
unhelpful for 21st century readers who can now travel quickly between
latitudes and experience variations in twilight lengths due to surface
rotational speeds.



The ridiculous Ra/Dec explanation using 'Sun angle' descent is from a

community with a lack of sense of solar system scale as individual

objects or the distances between them -

The definition of twilight never mentions the RA/DEC system, which has nothing whatsoever to do with twilight. Astronomical twilight isn't over until the sun is 18 degrees down, pure and simple.


The Ra/Dec system is a homocentric ideology and adrift of all cause
and effect to the extent that something with so much common sense as
the correlation between rotational speeds and twilight lengths
suffering the same dismal dithering.I enjoy the gentleness of twilight
and never require a reader to see it in any different terms but should
they choose to dwell on the cause as a location sweeps through the
circle of illumination,they are not likely to opt for a 'descending
Sun' as opposed to a rotating planet.



Behind the simple explanation of twilight length using surface speeds

is the orbital twilight at the polar coordinates around the equinoxes

as they are carried around in a circle to the central Sun and why the

old perception of axial precession must be dismissed and move to a

long term orbital trait -

http://en.wikipedia.org/w/index.php?...ecession.svg&p....

Axial precession is only important on a very long 26,000 year scale and never belongs in any conversation about the length of twilight... once again you have used a link that is totally inappropriate as an illustration for the point you are trying to make.


Come the equinox,the polar coordinates turn through the circle of
illumination by way of a separate orbital cause hence the old axial
precession perspective is getting in the way of comprehending the
single day/night cycle to the central Sun with the polar coordinates
carried around in a circle that is now occupied with a flawed view of
precession.Kepler's modification of orbital geometries set the
precedent and this is probably a far greater modification that is long
overdue,it is not a boast,it is an observational certainty -

http://www.daviddarling.info/images/...gs_changes.jpg

The Earth behaves just the same way although you feel it is changing
perspectives between Earth and Uranus.The physical consideration of
distance between the planets exclude that possibility and the turning
of the rings and polar coordinates to the central Sun is a local
dynamic trait and not one of changing perspective,I wish you could
understand what I am saying but sometimes that is not possible but at
least thanks for trying.



I told you before,the natural tendency of the empiricist is to move

technical details,even simple one like these,into personal insults

becomes a waste of time and energy and you may again get the luxury of

saying whatever you wish without a response from me.

The fact is that you have never actually responded to me. You don't actually answer any questions asked of you. I (we) present facts, you present "intuitive interpretation".

You have repeatedly said that the return of a star does not correspond to the rotation of the Earth, and therefore you have been repeatedly asked what the return of a star means to you, but so far you have never answered this simple and direct question. Why not?


Simple,stellar circumpolar motion indicates axial orientation and
nothing more in dynamical terms,the daily return of a star as
determined by the 24 hour AM/PM cycle within the 365/366 day calendar
format excludes the possibility of using the observation as a
determination of the Earth's daily and orbital motions.The foundation
of all timekeeping is that the star Sirius does not appear from behind
the glare of the Sun are 4 consecutive years of 365 days but appears
after an additional day after the 4th cycle,this in turn forms the
basis for the averaging of the 24 hour day using the proportion of
`1461 rotations for 4 orbital cycles which in turn is converted into
the Lat/Long system.The Ra/Dec system is merely an outrigger of the AM/
PM and Lat/Long systems and a great convenience for those who know how
to use it properly and its limitations.



Finally, as per the dictionary, it is YOU who is the empiricist...

em·pir·i·cism *(m-pîr-szm)
n.
1. The view that experience, especially of the senses, is the only source of knowledge.

Your problem is that you observe the same things as the rest of us, but come up with different interpretations, which prove to be invalid, and no amount of provided evidence can alter your opinion. Math doesn't lie, and just because YOU don't fully understand the math does NOT mean it isn't true.


My problems are small compared to the student who faces a professor
who talks in terms of the angle of the descending Sun with all the
conviction of a person for whom 'above and below' are working
principles for planetary dynamics and terrestrial effects.It was the
vicious strain of empiricism that sequestered the Ra/Dec system and
turned a useful tool into a weapon.





There are several "real" astronomers hanging out around here and you would be well advised to try to learn some real science before it's too late.

You can't help yourselves with that headache inducing stuff and this
is fine,ultimately all this is getting sorted out here in such a way
that a simple insight weaves its way through so many different topics
and especially the distinction between daily twilight and its
rotational cause from the orbital twilight at the polar coordinates
which has a separate cause.I don't condescend to anyone about
learning,the satisfaction in seeing the distinction between daily and
orbital twilights emerge is enough

On 09/10/2012 05:54, oriel36 wrote:
The easiest of all insights to understand is why twilight lengths
diminish towards equatorial latitudes,the obvious reason being that
faster surface speeds passing through the circle of illumination cause
a rapid transition from daylight to darkness at the equator and the
transition becomes longer as the speeds diminish towards the polar
latitudes.


Your purported 'reason' doesn't explain why twilight length changes
between summer and winter.
Clearly it takes more insight than you're capable of.

On Oct 11, 11:17*pm, OG wrote:
On 09/10/2012 05:54, oriel36 wrote:

The easiest of all insights to understand is why twilight lengths
diminish towards equatorial latitudes,the obvious reason being that
faster surface speeds passing through the circle of illumination cause
a rapid transition from daylight to darkness at the equator and the
transition becomes longer as the speeds diminish towards the polar
latitudes.

Your purported 'reason' doesn't explain why twilight length changes
between summer and winter.

Oh c'mon,we live in the 21st century and there is so much visible data
out there,we have people living and researching at the polar outposts
and it makes so much common sense to distinguish daily twilight and
its cause from polar twilight and its separate cause instead of
trying to bundle twilight lengths between equatorial and polar
latitudes together using a ridiculous 'Sun angle' descent.

It is 5 AM here in the Western isles of Europe and the circle of
illumination is well over a thousand miles away yet in a few hours my
location will sweep through that circle and that lovely light
transition of the dawn event will begin -

http://www.sat24.com/de/?animation=true&ir=false

On an orbital scale,perhaps a magnification enthusiast can tell me
whether the cameras on the Mars vehicle are powerful enough to take a
snapshot of the Earth at various points of its orbit as we do now of
Venus so that we can witness polar dawn and twilight as the polar
coordinates are carried around in a circle by the orbital behavior of
the Earth -

http://www.masil-astro-imaging.com/S...age%20flat.jpg

So,the major modification is clearly distinguishing polar twilight
from daily twilight using two separate causes and different approaches
are welcome as are graphics until actual imaging of the Earth from a
distance over an annual orbit shows something similar to the montage
of photos of Venus .


Clearly it takes more insight than you're capable of.

You know,this is at the developmental stage as part of a greater
study and while twilight lengths react to the daily and orbital
motions of the Earth ,it provides a foundation for looking at how the
tides react to the same dynamics and clearly daily and orbital
components must be separate whereas today everything is bundled in the
equatorial coordinate system and is going nowhere.

Not everyone is going to get the assertion immediately yet some
will,even in glimpses,so it depends on there the individual is coming
from that makes the difference.The appearance for the arguments of
planetary dynamics itself demonstrates a cautious approach* due to
uncertainty and older prejudices and even today there is a dispute
over what constitutes the resolution of retrogrades.The same applies
with twilight lengths as the polar twilight is a distinct event with a
separate cause .


* http://homepages.wmich.edu/~mcgrew/chain.htm

A rough back of the envelope calculation is sufficient to carry the
point specifically related to daily twilight variations and setting
aside the separate polar twilight at the equinox.

At a location of Dublin,Ireland the distance for each degree of
Longitude is around 40 miles for each degree and 4 minutes of clock
time within the AM/PM and Lat/Long systems so that a location sweeps
around at roughly 600 miles per hour and considerably less than the
1037.5 miles per hour at the equator.

http://www.csgnetwork.com/degreelenllavcalc.html

Setting aside atmospheric refraction,at the equinox a location at 55
degrees North covers 7 200 miles from the time it exits the circle of
illumination at dawn and re-enters it at twilight whereas at the
equatorial latitude the distance covered will be close to 12 500
miles.The surface speeds at different latitudes as it passes through
the transition zone between daylight and darkness are experienced at a
surface level as a rapid transition at the equator and a stretching
of dawn and twilight either side of the equator.

The community,such as it is, finds itself in a position where it has
to argue against the correlation between surface speeds indicative of
a round and rotating Earth and variations in twilight at different
latitudes in support of a ridiculous 'Sun angle' descent below the
horizon although it is not clear what they propose the Sun descend
into from above the horizon !.