Equinox twilight

The reason why people experience a rapid descent into darkness at the
equatorial latitudes and a longer twilight towards the polar latitudes
is, of course,due to the diminishing speeds from a maximum at the
equator so that a location there passes through the circle of
illumination more quickly there than at latitudes further North or
South.No reasonable person needs convincing much less an experienced
astronomer but these times are not normal circumstances and the
hideous explanation is based on the 'steepness' of the angle of the
descending Sun rather than the sensible explanation for why twilight
varies with latitude based on the geometry of a rotating sphere and
latitudinal speeds.

The seasonal variations in twilight reflect the changing angle between
the rotational orientation of the planet and the fixed circle of
illumination brought about by the way the planet turns once to the
central Sun as a component to its orbital motion,although is requires
a more complicated explanation using the polar coordinates to act like
a beacon for the orbital component,it is the only proper way to
proceed.

I see the enthusiasm of the 'oldtimers' has waned yet again,the
spectacular entrance back into the forum and then very little by way
of comment.The forum and the topics discussed have changed so much
over the years and this topic is quite an important astronomical one
for many reasons at not least that it gets rid of these 'steepness'
explanations and replaces them with a genuine one.In this day and age
to see a 'steepness' explanation is disappointing -



"When the sun sets due west – as it does on the day of an equinox –
the sun hits the horizon at the steepest possible angle, which hastens
the duration of sunset. Although the sunset duration varies by
latitude, the equinox sun sets in about 2 and 3/4 minutes at 40
degrees latitude (Denver, Philadelphia)."

http://earthsky.org/tonight/fastest-...d-equinox-time

On Thursday, September 20, 2012 9:03:21 AM UTC-7, oriel36 wrote:
The reason why people experience a rapid descent into darkness at the

equatorial latitudes and a longer twilight towards the polar latitudes

is, of course,due to the diminishing speeds from a maximum at the

equator so that a location there passes through the circle of

illumination more quickly there than at latitudes further North or

South.No reasonable person needs convincing much less an experienced

astronomer but these times are not normal circumstances and the

hideous explanation is based on the 'steepness' of the angle of the

descending Sun rather than the sensible explanation for why twilight

varies with latitude based on the geometry of a rotating sphere and

latitudinal speeds.



The seasonal variations in twilight reflect the changing angle between

the rotational orientation of the planet and the fixed circle of

illumination brought about by the way the planet turns once to the

central Sun as a component to its orbital motion,although is requires

a more complicated explanation using the polar coordinates to act like

a beacon for the orbital component,it is the only proper way to

proceed.



I see the enthusiasm of the 'oldtimers' has waned yet again,the

spectacular entrance back into the forum and then very little by way

of comment.The forum and the topics discussed have changed so much

over the years and this topic is quite an important astronomical one

for many reasons at not least that it gets rid of these 'steepness'

explanations and replaces them with a genuine one.In this day and age

to see a 'steepness' explanation is disappointing -







"When the sun sets due west – as it does on the day of an equinox –

the sun hits the horizon at the steepest possible angle, which hastens

the duration of sunset. Although the sunset duration varies by

latitude, the equinox sun sets in about 2 and 3/4 minutes at 40

degrees latitude (Denver, Philadelphia)."



http://earthsky.org/tonight/fastest-...d-equinox-time

http://tinyurl.com/bunpb3u

On Sep 20, 5:12*pm, palsing wrote:
On Thursday, September 20, 2012 9:03:21 AM UTC-7, oriel36 wrote:
The reason why people experience a rapid descent into darkness at the

equatorial latitudes and a longer twilight towards the polar latitudes

is, of course,due to the diminishing speeds from a maximum at the

equator so that a location there passes through the circle of

illumination more quickly there than at latitudes further North or

South.No reasonable person needs convincing much less an experienced

astronomer but these times *are not normal circumstances and the

hideous explanation is based on the 'steepness' of the angle of the

descending Sun rather than the sensible explanation for why twilight

varies with latitude *based on the geometry of a rotating sphere and

latitudinal speeds.

The seasonal variations in twilight reflect the changing angle between

the rotational orientation of the planet and the *fixed circle of

illumination brought about by the way the planet turns once to the

central Sun as a component to its orbital motion,although is requires

a more complicated explanation using the polar coordinates to act like

a beacon for the orbital component,it is the only proper way to

proceed.

I see the enthusiasm of the 'oldtimers' has waned yet again,the

spectacular entrance back into the forum and then very little by way

of comment.The forum and the topics discussed have changed so much

over the years and this topic is quite an important astronomical one

for many reasons at not least that it gets rid of these 'steepness'

explanations and replaces them with a genuine one.In this day and age

to see a 'steepness' explanation is disappointing -

"When the sun sets due west – as it does on the day of an equinox –

the sun hits the horizon at the steepest possible angle, which hastens

the duration of sunset. Although the sunset duration varies by

latitude, the equinox sun sets in about 2 and 3/4 minutes at 40

degrees latitude (Denver, Philadelphia)."

http://earthsky.org/tonight/fastest-...d-equinox-time

http://tinyurl.com/bunpb3u

Sometimes people learn from natural behaviors,in this case you are
mobbing which serves no purpose and none of the species that come
under the irritating mobbing tactic respond and with good reason,you
naturally don't understand why but it is,after,wasted energy to
respond,nothing more or less.If all you can do is answer with a quote
designed to diminish a human being then so be it,you have plenty of
company here.

http://en.wikipedia.org/wiki/Mobbing_(animal_behavior)

So,for those of higher human capabilities,and I am not condescending
to anyone despite appearances,there is the chance to correlate
twilight lengths with different latitudinal speeds as a daily event
and then separately,the variations in length of twilight as an
seasonal event or indeed the spectacular twilight now happening North
of the Arctic circle as the polar coordinates turn through the circle
of illumination and into polar darkness.

Watching the Sun rise the other morning above the horizon in an area
dotted with 5200 year old equinox markers is just one of those
privileges as an astronomer,a type of kinship that doesn't make this
world a lonely place and while the observation of the Sun rising can
be just as loved as the actual daily dynamic that causes it,we have to
allow the details of planetary dynamics also and especially the
specifics such as why twilight variations correlate with latitudinal
speeds rather than trying to mix everything up with the Sun's
'steepness' of descent.

This is the 21st century and I wish readers would treat it as such.

No offence to those who define the Equinox in Ra/Dec celestial sphere
terms of the Sun crossing a imaginary celestial equator using the
calendar system as a foundation,the actual dynamic behind the equinox
is far more satisfying as it turns the North and South Pole rotational
coordinates to a position that are at right angles to the central Sun.

I have no objections whatsoever to the astrophotographers and their
calendar based Ra/Dec perspective however I do believe people can do
much better and adopt a more 21st century approach to this great
astronomical and global event and the symmetry between daylight and
darkness,at least up to a point.The serious business of discussing
the Earth's equatorial climate is founded on a better perspective and
this new approach is based on using the polar coordinates as a beacon
for a single annual rotation to the central Sun where the North and
South poles turn to the central Sun rather than the older variable
'tilt' explanation.

Again,people can do much better for themselves and for the future
community whether they are interested adults or students,after 500
years with an awkward explanation,we can now use planetary comparisons
to arrive at more streamlined conclusions for global climate and
latitudinal temperature fluctuations known to us as the seasons.