[FRIAM] Sunset and Sunrise

Fri Jan 1 14:27:12 EST 2021

Thank you, Roger!

---
Frank C. Wimberly
140 Calle Ojo Feliz,
Santa Fe, NM 87505

505 670-9918
Santa Fe, NM

On Fri, Jan 1, 2021, 11:41 AM Roger Critchlow <rec at elf.org> wrote:

> Steve got most of it.
>
> The short explanation is that days get shorter or longer because of the
> tilt of the earth's axis moves the sun's path north and south.  The sun's
> path follows lines of latitude in the sky, ie arcs parallel to the equator,
> so the arcs are shorter when the sun is on the other side of the equator
> and longer when the sun is on the same side of the equator.  And if you're
> far enough from the equator the arc can become a circle or be entirely
> below the horizon depending on the season.
>
> But note that the sun's latitude changes continuously, so it actually
> traces a helix in latitude screwing its way south to the winter solstice,
> and then screwing its way north to the summer solstice.  Talking of the
> path as parallel to latitude lines amounts to using a fixed latitude for
> the day.  The helical motion makes sunsets a little more wintry than
> sunrises from midsummer to midwinter, and vice versa from midwinter to
> midsummer.
>
> And note that the earth's motion in orbit is fastest around its
> perihelion, January 4, so the speed of the sun through the helix is fastest
> in January and slowest in July.  This makes the time from sunrise to sunset
> a little shorter around the perhihelion.
>
> And finally note that sunrise and sunset occur when the sun is actually
> below the horizon:
>
>> For the special case of sunrise or sunset, the zenith is set to 90.833
>> degrees][ (the approximate correction for atmospheric refraction at sunrise
>> and sunset, and the size of the solar disk), [...]
>
> This makes the time from sunrise to sunset a little longer when the sun's
> path makes a shallower angle with the horizon, ie around the winter
> solstice in north temperate regions.
>
> So, yes, it depends on the tilt of the earth's axis to the ecliptic, on
> the eccentricity of the earth's orbit relative to a circle, and very much
> on where the observer is located on the earth.
>
> My earlier failed explanation derailed because I was trying to make the
> eccentricity correction go in the opposite direction than it does.
>
> -- rec --
>
> On Thu, Dec 31, 2020 at 11:43 PM Steve Smith <sasmyth at swcp.com> wrote:
>
>>
>> and this https://www.timeanddate.com/astronomy/solar-analemma.html
>> provides some visual intuition, but the text doesn't quite lead *me* to a
>> succinct explanation.    I could ramble on speculatively but the main thing
>> I take away from this is that the *axis* of the analemma reflects the tilt
>> of the earth axis relative to our orbit of the sun... and the eccentricity
>> of our orbit yields the sqew of the analemma away from an ellipse.   I
>> suspect these geometric arguments are buried in Roger's albebraic
>> description of same.
>>
>>
>> https://www.herts.ac.uk/about-us/media-centre/news/2020/longest-known-exposure-photograph-ever-captured-using-a-beer-can
>>
>> Science progresses by grad students forgetting what they're doing and
>> leaving their experiments running after they leave school?
>>
>> I was going to explain your rise/set/length paradox, but my explanation
>> got confused in my head.  But you can do it yourself.
>> https://www.esrl.noaa.gov/gmd/grad/solcalc/solareqns.PDF contains the
>> formulae for computing the time of sunrise and sunset given the
>> date, longitude, and latitude.  It's less than two pages of text and
>> they're in Boulder so they even mention Mountain Standard Time at one
>> point.  Hundreds of thousands of years of human worrying about when the sun
>> will rise and when it will set, all boiled down to 11 equations.
>>
>> -- rec --
>>
>>
>> On Wed, Dec 30, 2020 at 12:38 AM <thompnickson2 at gmail.com> wrote:
>>
>>> Yes.  I see.  Nifty. But it repeats the assertion that the tilting of
>>> the earth also has to do with it.  Could it be that the fact that the earth
>>> is not quite a sphere be playing a role, in  which case the tilting on the
>>> axis would make a difference?  Where are all our knowitall nerds when we
>>> need them.  (};-)]
>>>
>>> N
>>>
>>> Nicholas Thompson
>>>
>>> Emeritus Professor of Ethology and Psychology
>>>
>>> Clark University
>>>
>>> ThompNickSon2 at gmail.com
>>>
>>> https://wordpress.clarku.edu/nthompson/
>>>
>>>
>>>
>>>
>>>
>>> *From:* Friam <friam-bounces at redfish.com> *On Behalf Of *Frank Wimberly
>>> *Sent:* Tuesday, December 29, 2020 9:27 PM
>>> *To:* The Friday Morning Applied Complexity Coffee Group <
>>> friam at redfish.com>
>>> *Subject:* Re: [FRIAM] Sunset and Sunrise
>>>
>>>
>>>
>>> Try this one, Nick.  It sounds like what you're saying:
>>>
>>>
>>>
>>> http://wxguys.ssec.wisc.edu/2019/12/16/solarday/
>>>
>>> ---
>>> Frank C. Wimberly
>>> 140 Calle Ojo Feliz,
>>> Santa Fe, NM 87505
>>>
>>> 505 670-9918
>>> Santa Fe, NM
>>>
>>>
>>>
>>> On Tue, Dec 29, 2020, 8:18 PM <thompnickson2 at gmail.com> wrote:
>>>
>>> Frank,
>>>
>>>
>>>
>>> Andl notice another thing.  The sentence is, on its face, nonsense.  The
>>> tilting of the orbit has nothing to do with its elliptical shape.
>>>
>>>
>>>
>>> I have tried to figure out the answer to this question for years and the
>>> only explanation that I have come up with is that during the period from
>>> early December to early January, the days stay roughly the same length but
>>> noon moves.  It has to do with the analemma
>>> <https://www.space.com/3304-earth-closest-sun-dead-winter.html#:~:text=The%20noontime%20position%20of%20the%20Sun%20in%20the,line%20running%20through%20the%20analemma%20is%20the%20meridian.>.
>>> Notice that the day-to-day path of the highest sun is moving parallel to
>>> the horizon and perpendicular to the meridian during that period. If you
>>> think of that moment as “noon”, noon is moving.   But why the analemma?
>>> Your guess is as good as mine.
>>>
>>>
>>>
>>> Have you noticed that the rising full moon is moving rapidly up the
>>> horizon.  By march it will be rising in the NE.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Nicholas Thompson
>>>
>>> Emeritus Professor of Ethology and Psychology
>>>
>>> Clark University
>>>
>>> ThompNickSon2 at gmail.com
>>>
>>> https://wordpress.clarku.edu/nthompson/
>>>
>>>
>>>
>>>
>>>
>>> *From:* Friam <friam-bounces at redfish.com> *On Behalf Of *Frank Wimberly
>>> *Sent:* Tuesday, December 29, 2020 8:48 PM
>>> *To:* The Friday Morning Applied Complexity Coffee Group <
>>> friam at redfish.com>
>>> *Subject:* [FRIAM] Sunset and Sunrise
>>>
>>>
>>>
>>> This topic came up at a recent meeting.  The word "main" makes me wonder
>>> what the other reasons are.
>>>
>>>
>>>
>>> The main reasons for the *earliest* sunset to occur in early December
>>> and the *latest sunrise* to occur in January are the fact that Earth's
>>> axis is tilted (23.5°) and Earth's orbit around the sun is *not* a
>>> perfect circle shape.
>>>
>>>
>>>
>>> --
>>>
>>> Frank Wimberly
>>> 140 Calle Ojo Feliz
>>> Santa Fe, NM 87505
>>> 505 670-9918
>>>
>>>
>>>
>>> Research:  https://www.researchgate.net/profile/Frank_Wimberly2
>>>
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