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 <[email protected]> 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 <[email protected]> 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 <[email protected]> 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 >>> >>> [email protected] >>> >>> https://wordpress.clarku.edu/nthompson/ >>> >>> >>> >>> >>> >>> *From:* Friam <[email protected]> *On Behalf Of *Frank Wimberly >>> *Sent:* Tuesday, December 29, 2020 9:27 PM >>> *To:* The Friday Morning Applied Complexity Coffee Group < >>> [email protected]> >>> *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 <[email protected]> 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 >>> >>> [email protected] >>> >>> https://wordpress.clarku.edu/nthompson/ >>> >>> >>> >>> >>> >>> *From:* Friam <[email protected]> *On Behalf Of *Frank Wimberly >>> *Sent:* Tuesday, December 29, 2020 8:48 PM >>> *To:* The Friday Morning Applied Complexity Coffee Group < >>> [email protected]> >>> *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 >>> >>> - .... . -..-. . -. -.. -..-. .. ... -..-. .... . .-. . >>> FRIAM Applied Complexity Group listserv >>> Zoom Fridays 9:30a-12p Mtn GMT-6 bit.ly/virtualfriam >>> un/subscribe http://redfish.com/mailman/listinfo/friam_redfish.com >>> archives: http://friam.471366.n2.nabble.com/ >>> FRIAM-COMIC http://friam-comic.blogspot.com/ >>> >>> - .... . -..-. . -. -.. -..-. .. ... -..-. .... . .-. . >>> FRIAM Applied Complexity Group listserv >>> Zoom Fridays 9:30a-12p Mtn GMT-6 bit.ly/virtualfriam >>> un/subscribe http://redfish.com/mailman/listinfo/friam_redfish.com >>> archives: http://friam.471366.n2.nabble.com/ >>> FRIAM-COMIC http://friam-comic.blogspot.com/ >>> >> >> - .... . -..-. . -. -.. -..-. .. ... -..-. .... . .-. . >> FRIAM Applied Complexity Group listserv >> Zoom Fridays 9:30a-12p Mtn GMT-6 bit.ly/virtualfriam >> un/subscribe <http://bit.ly/virtualfriamun/subscribe> >> http://redfish.com/mailman/listinfo/friam_redfish.com >> archives: http://friam.471366.n2.nabble.com/ >> FRIAM-COMIC http://friam-comic.blogspot.com/ >> >> - .... . -..-. . -. -.. -..-. .. ... -..-. .... . .-. . >> FRIAM Applied Complexity Group listserv >> Zoom Fridays 9:30a-12p Mtn GMT-6 bit.ly/virtualfriam >> un/subscribe http://redfish.com/mailman/listinfo/friam_redfish.com >> archives: http://friam.471366.n2.nabble.com/ >> FRIAM-COMIC http://friam-comic.blogspot.com/ >> > - .... . -..-. . -. -.. -..-. .. ... -..-. .... . .-. . > FRIAM Applied Complexity Group listserv > Zoom Fridays 9:30a-12p Mtn GMT-6 bit.ly/virtualfriam > un/subscribe http://redfish.com/mailman/listinfo/friam_redfish.com > archives: http://friam.471366.n2.nabble.com/ > FRIAM-COMIC http://friam-comic.blogspot.com/ >
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