Shortest Day 2006

With the Winter Solstice occuring at 0:22 UT on 22/12/2006 this leaves
me a bit uncertain as to which is the shortest day this year. Is it the
21st or the 22nd?

I used Cartes du Ciel and SkyMap 11 to try to work out which was the
shorter. Cartes du Ciel seems unable to distinguish between the length
of the two dates. SkyMap 11 indicates that the 22nd has 1 second less
daylight and is thus the shortest day. Is this correct?

This also raises the question of what set of circumstances would result
in both days either side of the solstice being of equal length so that
we had two shortest days - to an accuracy of one second.

Cheers - Merry Christmas
Phil Meades

Phil Meades wrote:
With the Winter Solstice occuring at 0:22 UT on 22/12/2006 this leaves
me a bit uncertain as to which is the shortest day this year. Is it the
21st or the 22nd?

I used Cartes du Ciel and SkyMap 11 to try to work out which was the
shorter. Cartes du Ciel seems unable to distinguish between the length
of the two dates. SkyMap 11 indicates that the 22nd has 1 second less
daylight and is thus the shortest day. Is this correct?

This also raises the question of what set of circumstances would result
in both days either side of the solstice being of equal length so that
we had two shortest days - to an accuracy of one second.

Cheers - Merry Christmas
Phil Meades

Logic would say that the 22nd is the shortest period of daylight. I've
had a look at a number of websites, and most can't differentiate.
However the mach.usno.navy.mil web site gives the 22nd for N56 000EW 1
minute shorter which is not completely true, but it does favour the
22nd. Your reading of one second (or less) from SkyMap is probably the
most accurate imho.

John DH

JohnDH wrote:
Phil Meades wrote:
With the Winter Solstice occuring at 0:22 UT on 22/12/2006 this leaves
me a bit uncertain as to which is the shortest day this year. Is it the
21st or the 22nd?

I used Cartes du Ciel and SkyMap 11 to try to work out which was the
shorter. Cartes du Ciel seems unable to distinguish between the length
of the two dates. SkyMap 11 indicates that the 22nd has 1 second less
daylight and is thus the shortest day. Is this correct?

This also raises the question of what set of circumstances would result
in both days either side of the solstice being of equal length so that
we had two shortest days - to an accuracy of one second.

Cheers - Merry Christmas
Phil Meades

Logic would say that the 22nd is the shortest period of daylight. I've
had a look at a number of websites, and most can't differentiate.
However the mach.usno.navy.mil web site gives the 22nd for N56 000EW 1
minute shorter which is not completely true, but it does favour the
22nd. Your reading of one second (or less) from SkyMap is probably the
most accurate imho.

John DH

Just to add

at 60 north it seems to favour the 21st.

The length of a day in astronomy is very specific and refers to the
Total length of a daily cycle which is global occurence .What you are
talking about is daylight/darkness asymmetry and very few people ever
try to make the distinction between the correct astronomical
description and the civil description of longer/shorter days.

The pseudo-dynamic of variable axial tilt was introduced in the late
17th century and falsely applied to the noon Equation of Time
correction which equalises the variations of the Total length of a
day,you can still see the hapless analemma monster to explain the
Equation of Time that way -

http://imagine.gsfc.nasa.gov/docs/as...s/980116c.html

So,you look elsewhere than daylight/darkness for the 'shortest
day',ayt least in astronomical terms.Who knows !, maybe next year
somebody will be able to give you the correct astronomical answer.


Phil Meades wrote:
With the Winter Solstice occuring at 0:22 UT on 22/12/2006 this leaves
me a bit uncertain as to which is the shortest day this year. Is it the
21st or the 22nd?

I used Cartes du Ciel and SkyMap 11 to try to work out which was the
shorter. Cartes du Ciel seems unable to distinguish between the length
of the two dates. SkyMap 11 indicates that the 22nd has 1 second less
daylight and is thus the shortest day. Is this correct?

This also raises the question of what set of circumstances would result
in both days either side of the solstice being of equal length so that
we had two shortest days - to an accuracy of one second.

Cheers - Merry Christmas
Phil Meades

In message . com, Phil
Meades writes
With the Winter Solstice occuring at 0:22 UT on 22/12/2006 this leaves
me a bit uncertain as to which is the shortest day this year. Is it the
21st or the 22nd?

I used Cartes du Ciel and SkyMap 11 to try to work out which was the
shorter. Cartes du Ciel seems unable to distinguish between the length
of the two dates. SkyMap 11 indicates that the 22nd has 1 second less
daylight and is thus the shortest day. Is this correct?

This also raises the question of what set of circumstances would result
in both days either side of the solstice being of equal length so that
we had two shortest days - to an accuracy of one second.

Cheers - Merry Christmas
Phil Meades


2007-12-22 06:12 is the solstice according to

http://www.hermetic.ch/cal_sw/ve/ve.htm

But for length of day it looks like a dead heat for 21st and 22nd for
Edinburgh - two shortest days !

http://www.timeanddate.com/worldclock/astronomy.html

Length of day
Date Sunrise Sunset This day Difference

21 Dec 2006 08:42 15:40 6h 57m 29s - 0m 08s
22 Dec 2006 08:43 15:40 6h 57m 29s - 0m 00s

For a different longitude 6 hours further west , 21st is shorter
since the solstice occurs on the 21st

Brian
--
Brian Howie

In message , Brian Howie
writes

2007-12-22 06:12 is the solstice according to

http://www.hermetic.ch/cal_sw/ve/ve.htm

Oops a year out !

2006-12-22 00:22

Brian
--
Brian Howie

Brian Howie wrote:
In message , Brian Howie
writes

2007-12-22 06:12 is the solstice according to

http://www.hermetic.ch/cal_sw/ve/ve.htm

Oops a year out !

2006-12-22 00:22

Brian
--
Brian Howie

My astronomical timekeeping ancestors observed the length of the daily
cycle using the noon reference and knew it was unequal with each cycle
..They equalised the variations of the total length of a day to a 24
hour standard and allowed one 24 hour day to elapse seamlessly into the
next 24 hour day.This keeps the astronomical principles for the 24 hour
day and the varying length of a day clear from the civil convenience of
lengthening and shortening daylight hours.

Maybe next year there will be genuine astronomers who can take the easy
to understand relationship between the Total length of the natural day
and how it was reduced to the equable 24 hour day,the fact that one 24
hour day elapses seamlessly into the next 24 hour day and then apply
the heliocentric principle which correlates clocks with axial rotation
at precisely 4 minutes for each degree of rotation.

Being a shared timekeeping heritage means that I am only presently the
clearly defined parameters for clocks,astronomy,terrestrial longitudes,
axial rotation as an independent motion ect.There is a cult group of
people who believe in an alterantive means to justify the Earth's
motions but who is going to pay them any attention when their geometry
looks like this -

http://www.opencourse.info/astronomy...phere_anim.gif

These are the people who work off the 'longest/shortest' day in the
most astronomically vulgar terms,at least those who call themselves
astronomers.

Oops indeed !.