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As noted, the day with the least total amount of sunlight is day of the sol=
stice. The analemma (which is caused by a combination of two effects: the 2=
3.5=B0 inclination of the Earth's rotation axis and the eccentricity of the=
Earth's orbit) is the reason why the earliest sunset occurs on Dec. 9 and =
the latest sunrise will not be until Jan. 2. (Earth is closest to the Sun o=
n Jan. 4)
The best way to visualise the effect of the analemma is to start off by ima=
gining that there was no effect and that the analemmas's shape was that of =
a vertical pole. The Sun at solar noon (when highest in the sky) would chan=
ge it's altitude by 23.5 x 2 =3D 47=B0 going from the top of the pole on th=
e summer solstice, to the bottom of the pole on the winter solstice.
At a latitude of 45=B0, if you were to hold a vertical pole at arm's length=
then the "up and down" motion of the Sun over a year would be vertical fac=
ing south, but the top would be tipped 45=B0 to the left if you were holdin=
g it looking east, and the top would be tipped 45=B0 to the right if facing=
west. In this fashion, you would see that as you sweep the pole from east =
through south to west, that the sun would rise latest and set earliest on t=
he same day it is above the horizon the least (the day of the solstice).
Now replace the vertical pole with the analemma, which is shaped like a fig=
ure 8. If you do the same east to west sweep, you will see that when the Su=
n is to the right of the lowest position (to the right as you are looking a=
t it), that part of the analemma will touch the western horizon before the =
lowermost point! This the sunset will be earlier that it will be on the sol=
stice. Similarly, after the solstice, the lower left part of the analemma w=
ill rise above horizon after the lowermost point, giving you the latest sun=
rise after the solstice.
Pat
On Dec 23, 2014, at 11:56 AM, David & Alison Webster wrote:
Hi All, Dec 23, 2014
Perhaps the astronomers can put a quantitative edge on this but, in qua=
litative terms, the discrepancy between apparent sun movement and clock mov=
ement is responsible for such apparent irregularities.
The excecutive summary would state that the clock moves ahead on mean t=
ime whereas the sun, being a jolly fellow, is not in the least mean.
If you examine the analemma you will see that from early Sept. to 20 De=
c. the clock is behind the sun but starting about Nov 1, the clock begins t=
o gain on the sun and continues to gain until early Feb. [By Dec 20 the clo=
ck is ahead of the sun. ] Because day length, measured by the clock is of c=
onstant length this must mean that sun day length during this period, when =
the clock gains on the sun, is less than 24 clock hours in length.
This I think arises from our good fortune in the Northern Hemisphere th=
at the earth is nearest the sun about Dec 20.
Yt, DW
----- Original Message -----
From: desolatechair<mailto:desolatechair@gmail.com>
To: naturens<mailto:naturens@chebucto.ns.ca>
Sent: Tuesday, December 23, 2014 8:35 AM
Subject: Re: [NatureNS] why aren't the days getting longer
Andy
There is some rounding at play, but basically sunrise keeps getting later u=
ntil around the 25th. The earliest sunset is around the 17th, and after th=
e 21st it starts getting later but the incremental change is not enough to =
make up for what we continue to lose in the morning. Takes about a week af=
ter the solstice to start making a net gain.
Regards
Jamie
Sent from Samsung Mobile
-------- Original message --------
From: Andy Moir/Christine Callaghan
Date:12-23-2014 8:09 AM (GMT-04:00)
To: NatureNS
Subject: [NatureNS] why aren't the days getting longer
According to the environment canada weather page, we actually got 1
minute less sunlight today than yesterday. I understand about solar
noon (I think), so I'm not really expecting sunrise to be earlier each
day...but the total hours of sunlight should be increasing, not
decreasing, after the solstice, I thought. What up with that? Is it
perhaps some rounding issue with the Environment Canada calculator? I
get the same result (less sunlight time, when I go to the NOAA solar
Calculator)
Thanks.
Andy
(who's always dealing with the big issues in life)
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Dalhousie University
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As noted, the day with the l