[NatureNS] why aren't the days getting longer

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Date: Sat, 27 Dec 2014 14:21:54 -0400
From: Burkhard Plache <burkhardplache@gmail.com>
To: naturens@chebucto.ns.ca
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You are (I am guessing) making assumptions regarding the
definitions of the coordinates (here: latitude) that are incorrect.
The altitude is measured / calculated from local horizontal,
which differs from the angle when connecting the 45 degree point
to the center of the ellipsoid.
If you make an over-ellipsed sketch (e.g., North-South being
half of East-West) the discrepancy should become clear.
Keep in mind, though, that e.g., 45 degree latitude in the
ellipsoid coordinate system is *not* obtained by drawing a 45
degree line from the center of the ellipsoid. On the ellipsoid,
45 degree latitude is where the local vertical stands at a 45 degree
angle versus the equator plane (or versus the rotational axis).

Calculations in ellipsoid coordinates are unfortunately not
'closed formula' but require numerical approximations.

Burkhard


On Sat, Dec 27, 2014 at 11:02 AM, David & Alison Webster
<dwebster@glinx.com> wrote:
> Hi All,                                Dec 27, 2014
>    As an exercise in reasoning I attempted to calculate winter minimum
> altitude of the sun at solar noon for two locations Kings County (Lat of
> 44o44' given) and Halifax (Lat of 44o39' given).
>
>    With the earth sliced in two along the meridian, minimum altitude (Min),
> if my reasoning is correct, should  be equal to
>  Min = 90 -(Lat+23o26')
>    But for Kings Co. I get Min = 21.83o lower than given of 21.9o by 0.07o
> and for
> Halifax I get Min = 21.92o lower than given of 22.0o by 0.08o.
>    Is this discrepancy due the the earth not being quite spherical or
> something else ?
> Yt, Dw, Kentville
> ----- Original Message ----- From: "Burkhard Plache"
> <burkhardplache@gmail.com>
> To: <naturens@chebucto.ns.ca>
> Sent: Thursday, December 25, 2014 1:31 PM
> Subject: Re: [NatureNS] why aren't the days getting longer
>
>
>> Tabulated sunrise / sunset times are given at:
>> http://www.timeanddate.com/sun/canada/halifax
>>
>> And indeed, the days *are* getting longer.
>>
>> Burkhard
>>
>>
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