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Hi Sherman, Patrick & All, Dec 10, 2008
Thanks as usual Sherman for the interesting post but Patrick, the =
graph does not show why the dates of earliest sunset... don't coincide =
with the solstice it shows how they don't coincide.
I have not looked at this for some years (8 perhaps ?) but the =
fundamental 'cause' of this apparent discrepancy is I think (largely if =
not entirely) due to the practice of expressing sunrise and sunset in =
terms of mean solar days and these depart from actual solar days. =
Consequently the clock (i.e. time expressed in mean solar days) is =
variously ahead of or behind the sun; thus the Analemma.
Yt, DW, Kentville=20
----- Original Message -----=20
From: Patrick Kelly=20
To: naturens@chebucto.ns.ca=20
Sent: Wednesday, December 10, 2008 3:19 PM
Subject: Re: [NatureNS] Earliest Sunset Today
Hi Sherman:
Amazing. That one picture finally showed me why the dates of earliest =
sunset and latest sunrise (and vice versa in the summer) aren't the =
same as solstices. It's because the analemma is tipped. As they say in =
Star Trek: Shaka, his eyes open!
Way to go Sherm!
Patrick
On Dec 10, 2008, at 2:30 PM, Sherman Williams wrote:
For those near 45 degrees north latitude, TODAY marks the EARLIEST =
SUNSET (about 4:34 p.m. here in Avonport). Starting tomorrow the Sun =
begins to set a little later, not by any large amount, but by Dec 31 Sun =
is setting about 11 minutes later than today (4:45 p.m., about the time =
Sun was setting on Nov 17th). Latest sunrise is not until Jan 2nd. =
December 21st is the shortest daylight.
Thinking about this, I created a diagram (using Starry Night =
software) to show Sun's position relative to the horizon at about 4:35 =
p.m. each day through December. It is actually the very southern tip of =
the analemma, when the Sun is near the winter solstice, as it is now.
Diagram at http://web.mac.com/sherm39/iWeb/Site/analemma1.html
or http://web.mac.com/sherm39/iWeb/Site/main_index.html
Sherman
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Patrick Kelly
Director of Computer Facilities
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Faculty of Architecture and Planning
Dalhousie University
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PO Box 1000 Stn Central 5410 Spring Garden Road
Halifax, Nova Scotia B3J 2X4 Halifax, Nova Scotia B3J 2X4
Canada Canada
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Phone:(902) 494-3294 FAX:(902) 423-6672 =
E-mail:patrick.kelly@dal.ca
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<DIV><FONT face=3DArial size=3D2>Hi Sherman, Patrick & =
All, =20
Dec 10,=20
2008</FONT></DIV>
<DIV><FONT face=3DArial size=3D2> Thanks as usual =
Sherman for the=20
interesting post but Patrick, the graph does not show =
<STRONG>why</STRONG> the=20
dates of earliest sunset... don't coincide with the solstice it shows=20
<STRONG>how </STRONG>they don't coincide.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2> I have not looked at =
this for=20
some years (8 perhaps ?) but the fundamental 'cause' of this apparent=20
discrepancy is I think (largely if not entirely) due to the =
practice of=20
expressing sunrise and sunset in terms of mean solar days and these =
depart from=20
actual solar days. Consequently the clock (i.e. time expressed in mean =
solar=20
days) is variously ahead of or behind the sun; thus the =
Analemma.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Yt, DW, Kentville</FONT> </DIV>
<BLOCKQUOTE=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A title=3Dpatrick.kelly@DAL.CA =
href=3D"mailto:patrick.kelly@DAL.CA">Patrick=20
Kelly</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Dnaturens@chebucto.ns.ca=20
href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.ca</A> =
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Wednesday, December 10, =
2008 3:19=20
PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: [NatureNS] =
Earliest Sunset=20
Today</DIV>
<DIV><BR><