Here's a graph of earliest sunset/latest sunrises for various latitudes...
It is calculated by using the 12 +/- [acos{tan(latitude) .
tan(declination)}]/15 formula corrected to mean tim with the EoT
Best regards
Kevin
<<inline: Eariest:Latest.jpg>>
On 20 Dec 2010, at 14:26, Kevin Karney wrote:
> Dick
> Thanks for that correction. I am sorry I was being so insular and did not
> think it all through.
>
> One is seeing the interplay between two equations :
> 1) sunset/rise being (more or less) = 12 +/- [acos{tan(latitude) .
> tan(declination)}]/15 with declination change rather minimal around the
> solstice
> 2) equation of time changing rapidly around the winter solstice.
>
> There is a third influence - but I think it probably plays an insignificant
> part - the difference between the usually quoted geocentric equation of time
> and its topocentric cousin - which varies the equation of time by up to a
> second dependent on both time of day and latitude.
>
> Best regards
> Kevin
>
> On 20 Dec 2010, at 12:39, [email protected] wrote:
>
>> The date of earliest sunset depends on Latitude and is not
>> always Dec 14. See: http://www.idialstars.com/eass.htm
>>
>>
>>
>>
>>> Dear Colleagues
>>>
>>> In the depths of a freezing Northern winter, there's time to think about
>>> days of special interest. There are six significant solar dates around
>>> this time of the year.
>>>
>>> Three are special and probably known to all...
>>> 21st December - half an hour before midnight - the Winter Soltice
>>> 25th December - not only Christmas day, but one of the four days in the
>>> year when the equation-of-time is zero.
>>> 3rd January - Perihelion when the Earth is closest to the Sun,
>>>
>>> One day is perhaps of interest only to the serious heliochronometer
>>> user...
>>> 23rd December - the day when the equation of time is changing at its
>>> maximum rate of almost 30 secs/day
>>>
>>> Two days are nothing more than obscure, except to the numerically obsessed
>>> - or to those who like strange questions to ask on quiz nights....
>>> 14th December - the day on which the Sun sets earliest in the day
>>> 29th December - the day on which the Sun rises latest in the day
>>> See the graph below. If you wonder why this is so, it is because there are
>>> two effects in play (a) the daily change in sunrise/sunset as a result of
>>> declination change is minimal around the solstice and (b) the effect of
>>> the equation of time with its large eccentricity component as the Sun
>>> races forward towards perihelion.
>>>
>>> p.s. the graphs are for 54 degrees North latitude; the y-axis scale will
>>> change at other latitudes.
>>> p.p.s. dates are UT - so they may vary with your local longitude.
>>>
>>> Have a wonderful Christmas season.
>>>
>>> Kevin Karney
>>>
>>> ---------------------------------------------------
>>> https://lists.uni-koeln.de/mailman/listinfo/sundial
>>>
>>>
>>
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