OK, I don’t exactly know the right terminology, so here’s the question: Why does the winter solstice, being the shortest day of the year, not have both the earliest sunset and latest sunrise of the year?
According to the US Naval Observatory Sunrise/Sunset table , the earliest sunset of the year occurs around December 9th, but the latest sunrise of the year occurs around January 4th. (This is for coordinates E142:23, N44:55, GMT -9).
My flawed layman’s math tells me that the sun’s shadow across the earth makes a parabola of daylight. Parabolas are symmetrical. Therefore, the solstice should have both the latest sunrise and earliest sunset, and then every day before or after would have an equally changed sunrise and sunset. But this is definitely not the case.
Please take this as a cry for help in understanding basic 3-D geometry. I have never been good at understanding the prorated volume of an abraded frenulum or whatever it is you mathemeticians call problems of this type.
I’ll post the answer furnished by a well know astronomet to the sunrise/sunset after others have an opportunity to supply the answer. The equation of time is NOT the answer.
You forgot to start a new thread on another question in the same theread you hijacked this topic from. Namely:
I started a thread on a question I wanted answered from a different thread. If you have a question you want answered, you’re free to start your own.
Oddly enough, I think the question I’m asking is actually a question that you originally raised on that very thread…
I brought your question into this new thread… so what’s your complaint?
Lastly, a “hijack” is when you jump on someone’s topic and use it to talk about unrelated topics. I started this topic specifically to avoid hijacking the other guy’s thread.
This should answer your questions. Parabolas have nothing to do with it!
After you read the link, just as a little educational exercise, make it a point to start noticing when the Sun hits the north/south meridian where you live. This is easy for me because I work in downtown Chicago where the streets are laid out on a perfect north/south and east/west grid. Chicago is two degrees east of the central line of the Central Time Zone (90 degrees West), so “average” high noon is 11:52 a.m. The “equation of time” means that high noon comes between 16 minutes early and 14 minutes late, or between 11:36 a.m. and 12:06 p.m.
I always go to lunch around 11:45. And, depending on time of year, the Sun will either be just east of the North/South streets, or directly on the meridian, or just west. (In summer, of course, it’s shifted by an hour.) I notice little stuff like that. I’m weird that way.
The answer is this. You could define “one day” to be the amount of time between when the sun is at its peak on one day, to its peak on the next day. If the Earth went around the Sun in a perfectly circular path, this would be simple. But the path isn’t circular, it’s an ellipse. When we’re closer, generally in the winter in the northern hemisphere, the Sun’s position moves a little farther each day than in the summer, shifting “local noon” earlier or later than you would expect it. So we define the day as the average of all the days in the year, and some are a little longer and some are a little shorter.
I thought that this explanation was abbreviated the “equation of time,” but maybe I’m wrong.
The middle of the daylight period shifts throughout the year; this is pretty much the main reason for DST-type clock adjustments; it’s down to the tilt of the Earth’s axis - it isn’t exactly parallel to the day/night terminator (which is exactly perpendicular to the rays of the sun) - in spring, the northern hemisphere is ‘leaning’ toward the terminator, so locations further north (on the same longitude) experience sunrise and sunset earlier than locations further south - dawn gets earlier quicker than sunset gets later.
In autumn, the northern hemisphere is ‘leaning’ away from the terminator, so locations further north (on the same longitude) experience sunrise and sunset later than locations further south - sunset gets earlier quicker than dawn gets later.
Umm . . . No, it isn’t. The Equation of Time does not provide the motivation for Daylight Savings Time.
That’s how the axial tilt drives the change in seasons. The axial tilt is also partly responsible for the Equation of Time (the other factor is the Earth’s elliptical orbit), but in a different way.
Memo to mods and admins: This question comes up, as regularly as the seasons, with each solstice. A complete explanation of the Equation of Time and how it changes in the course of a year, and how those changes interract with latitude to drive the earliest and latest sunrises and sunsets, would require an essay of a couple thousand words. This would be a good subject for an SDSAB report.
Thanks for answering my question, FreddyThePig. If NASA says it’s due to the equation of time, I’m gonna have to go with the equation of time, PinGear’s comment notwithstanding.
It will help you visualize the what the combination of Earth’s axial tilt and eccentricity does to the apparent placement of the Sun in the sky for the same time every day, for the year…and how they end up as the “Equation of Time” analemmas that end up on globes.
PinGear, either you have an explanation or you don’t. Others have provided good explanations. If you have your own explanation, you’re welcome to share it. If you don’t, please stop dancing around the issue or responding to questions with questions. Thanks.
Then why did you bring up which hemisphere was tilted toward the Sun at which time of year? The effect of axial tilt on the Equation of Time, which drives the asymmetry in sunrises and sunsets, is the same in both hemispheres at both solstices.