Extrapolating from today's sunshine figures in Cambridgeshire we
would appear to be on course for the dullest winter on record.

Jack

Jack ) wrote:
Extrapolating from today's sunshine figures in Cambridgeshire we
would appear to be on course for the dullest winter on record.

Jack



An old chestnut at this time of year, when do the evenings start to get
lighter. I know it's before the winter solstice.

Joe
Wolverhampton
175m asl

"Joe Egginton" wrote in message
...
Jack ) wrote:
Extrapolating from today's sunshine figures in Cambridgeshire we
would appear to be on course for the dullest winter on record.

Jack



An old chestnut at this time of year, when do the evenings start to get
lighter. I know it's before the winter solstice.

A the good old Equation of Time.
Perhaps this will be the year I finally understand it......

From what I recall, the date is considerably before the solstice
perhaps as early as the 12th and conversely the mornings get
darker until into the New Year.

But *please* don't as me to explain it
--
Col

Bolton, Lancashire
160m asl

Col wrote:
"Joe Egginton" wrote in message
...

Jack ) wrote:

Extrapolating from today's sunshine figures in Cambridgeshire we
would appear to be on course for the dullest winter on record.

Jack



An old chestnut at this time of year, when do the evenings start to get
lighter. I know it's before the winter solstice.


A the good old Equation of Time.
Perhaps this will be the year I finally understand it......

From what I recall, the date is considerably before the solstice
perhaps as early as the 12th and conversely the mornings get
darker until into the New Year.

But *please* don't as me to explain it


I think it's something to do with the Earth doesn't spin around the Sun
in a perfect eclipse.

Joe
Wolverhampton
175m asl

On Fri, 1 Dec 2006 18:18:03 -0000, "Col"
wrote:

...
A the good old Equation of Time.
Perhaps this will be the year I finally understand it......
...

Obviously time for my annual post :-)

One of Keppler's Laws says that the area swept out by a body in its
orbit rotating about another is a constant for a given time. In an
elliptical orbit the distance of the orbiting body varies with respect
to the orbited body. For the area swept in a given time to be
constant, the speed of the orbiting body will be greater when its
closer to the orbited body and slower when it's further away.

Because the orbit of the Earth is elliptical, it's orbital speed
varies, but it's rotational speed about its axis is constant. The
effect of this is to skew sunrise, noon and sunset times
with respect to Standard Time. The amount of this skew is called the
Equation of Time and tables are published giving its value throughout
the year. Hence, to labour the point, the Sun is only due south at
noon at the Greenwich Meridian on about four dates in the year. At
other times it can be as much as twenty minutes earlier or later.
However, sunrise and sunset are roughly symmetrical about the time
that the Sun crosses the meridian so that if the Equation of Time on a
particular day is ten minutes then the Sun will cross the meridian ten
minutes after noon and sunrise and sunset will also occur ten minutes
later than if the Equation of Time didn't exist, but not symmetrically
about noon.

After the Winter Solstice logic indicates that sunrise should occur
earlier. However, around the Winter Solstice the Equation of Time is
increasing at a greater rate than sunrise is decreasing. Hence,
sunrise actually increases after the Solstice until early January when
the two rates equalise and after that sunrise moves in the 'right'
direction.

The Equation of Time is zero on or about 15th April, 14th June, 1st
September and 25th December.Only on those days will the Sun cross the
Greenwich Meridian at noon.

Phew!

--
Alan White
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll, Scotland.
Webcam and weather:- http://windycroft.gt-britain.co.uk/weather
Some walks and treks:- http://windycroft.gt-britain.co.uk/walks

"Alan White" On Fri, 1 Dec 2006 18:18:03 -0000, "Col"

wrote:

Obviously time for my annual post :-)

One of Keppler's Laws says that the area swept out by a body in its
orbit rotating about another is a constant for a given time. In an

Okay Alan, I lost you somewhere around Keppler? ;-)

Seriously though, thank you for that explanation...I've filed it for
reference.

Who knows, I could be a hero at the next table-quiz down the pub if they ask
the question...although it might take me to the end of the night to remember
and explain it all!!!


Joe

On Fri, 1 Dec 2006 18:58:19 -0000, "JCW" wrote:

...
Seriously though, thank you for that explanation...I've filed it for
reference.


So have I! It comes up every year.

Who knows, I could be a hero at the next table-quiz down the pub if they ask
the question...although it might take me to the end of the night to remember
and explain it all!!!

Wait until they've had more than you ;-)

--
Alan White
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll, Scotland.
Webcam and weather:- http://windycroft.gt-britain.co.uk/weather
Some walks and treks:- http://windycroft.gt-britain.co.uk/walks

Alan White wrote:

One of Keppler's Laws says that the area swept out by a body in its
orbit rotating about another is a constant for a given time. In an
elliptical orbit the distance of the orbiting body varies with respect
to the orbited body. For the area swept in a given time to be
constant, the speed of the orbiting body will be greater when its
closer to the orbited body and slower when it's further away.

I can remember the joyful suprise at suddenly understanding that during
an OU early Saturday morning broadcast after a damn good party. Everyone
else asleep, me still awake with "Understanding Space & Time" on the
telly... Keppler's equal area one and the one with Einstein on a train (and
in the station as the train swept past) with a light beam and two mirrors...
time dilation made easy!
Whatever happened to those OU programmes?

Les


Because the orbit of the Earth is elliptical, it's orbital speed
varies, but it's rotational speed about its axis is constant. The
effect of this is to skew sunrise, noon and sunset times
with respect to Standard Time. The amount of this skew is called the
Equation of Time and tables are published giving its value throughout
the year. Hence, to labour the point, the Sun is only due south at
noon at the Greenwich Meridian on about four dates in the year. At
other times it can be as much as twenty minutes earlier or later.
However, sunrise and sunset are roughly symmetrical about the time
that the Sun crosses the meridian so that if the Equation of Time on a
particular day is ten minutes then the Sun will cross the meridian ten
minutes after noon and sunrise and sunset will also occur ten minutes
later than if the Equation of Time didn't exist, but not symmetrically
about noon.

After the Winter Solstice logic indicates that sunrise should occur
earlier. However, around the Winter Solstice the Equation of Time is
increasing at a greater rate than sunrise is decreasing. Hence,
sunrise actually increases after the Solstice until early January when
the two rates equalise and after that sunrise moves in the 'right'
direction.

The Equation of Time is zero on or about 15th April, 14th June, 1st
September and 25th December.Only on those days will the Sun cross the
Greenwich Meridian at noon.

Phew!

--
Remove Frontal Lobes to reply direct.


By all means let's be open-minded, but not so open-minded that our
brains drop out. (Richard Dawkins)

http://armsofmorpheus.blogspot.com/

http://www.richarddawkins.net/index.php


Les Hemmings a.a #2251 SA

Les Hemmings wrote:
Whatever happened to those OU programmes?

Les


They were transferred to DVD so students no longer have to stay up late/get up
early/remember to tape them.


--
Gianna

Gianna wrote:
Les Hemmings wrote:
Whatever happened to those OU programmes?

Les


They were transferred to DVD so students no longer have to stay up
late/get up early/remember to tape them.

A loss to all of us then... (

L

--
Remove Frontal Lobes to reply direct.


By all means let's be open-minded, but not so open-minded that our
brains drop out. (Richard Dawkins)

http://armsofmorpheus.blogspot.com/

http://www.richarddawkins.net/index.php


Les Hemmings a.a #2251 SA