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seb146
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Solstice Questions

Fri May 15, 2020 3:21 am

I know there are other sites I could go to that would probably ask these question but I feel drown out.

I see that Stonehenge in England is live streaming the Summer Solstice. That is great and I will probably watch. How did they know the Solstice was happening when it was in the middle of the night? There are Stonehenge type monuments in the United States calibrated exactly but if the Solstice happens at, say, 0425 local time, how can they use the sun to calibrate these things? I guess this can be expanded to sundials as well.

I guess, because it is all relative, how can anyone know exactly when the Solstice happens when it is dark?
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Jalap
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Re: Solstice Questions

Fri May 15, 2020 7:35 am

seb146 wrote:
I know there are other sites I could go to that would probably ask these question but I feel drown out.

I see that Stonehenge in England is live streaming the Summer Solstice. That is great and I will probably watch. How did they know the Solstice was happening when it was in the middle of the night? There are Stonehenge type monuments in the United States calibrated exactly but if the Solstice happens at, say, 0425 local time, how can they use the sun to calibrate these things? I guess this can be expanded to sundials as well.

I guess, because it is all relative, how can anyone know exactly when the Solstice happens when it is dark?

Hmm, they most likely didn’t know exactly when Solstice happened. All they needed was a calendar. No?
Also, if their calibration was off 1 or 2 days, I doubt they would even have noticed.
 
tommy1808
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Re: Solstice Questions

Fri May 15, 2020 8:15 am

seb146 wrote:
how can anyone know exactly when the Solstice happens when it is dark?


measure the suns hight above the horizon during the day, once it is about a tenth of a degree lower than on maximum for your location you know you have to party tonight.

The concept of "time of day" didn´t really exist before reliable, relatively clocks. But there are plenty of ways to measure time with some precision, but the concept didn´t really compute as in "the solstice is at 4:20 am".
But if you want to track time, manpower isn´t an issue, and you don´t need to do it to the minute.... you can just have people walk around stuff and see how many rounds they make from noon to noon. Should be able to get within a few minutes of the correct time, especially when you train people to do it at a steady pace.

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einsteinboricua
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Re: Solstice Questions

Fri May 15, 2020 12:43 pm

The fact that the solstice is at 2144 UTC this year doesn't mean that it's a set time every year. Next year, it's expected to be at 0332 and the year after at 0914.

And while the point of maximum "solstice" is at that time, the progression of the Sun's path is so slow that whether they do it the day of or the day after it won't make much difference. Today's technology allows the tracking of the Sun's path across the sky and can give you the point of maximum solstice at an exact time. Back then, just noticing longer/shorter days and finding a way to track the Sun's path would have been enough to know when the maximum would be.
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frmrCapCadet
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Re: Solstice Questions

Fri May 15, 2020 1:57 pm

Precision in time in a particular place became critically necessary when railroads came along. Trains may need to meet up, but safety depended upon those meetings to take place as planned. Railroaders were amongst the first to all carry an accurate and precise watch, a pocket watch in fact. I have one which belonged to a 2nd or 3rd level uncle/cousin from the old days. Ships needed accurate time for navigation, but one per ship or so was enough. Trains - everyone needed to know times, probably to a minute or two.
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StarAC17
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Re: Solstice Questions

Fri May 15, 2020 2:06 pm

seb146 wrote:
I know there are other sites I could go to that would probably ask these question but I feel drown out.

I see that Stonehenge in England is live streaming the Summer Solstice. That is great and I will probably watch. How did they know the Solstice was happening when it was in the middle of the night? There are Stonehenge type monuments in the United States calibrated exactly but if the Solstice happens at, say, 0425 local time, how can they use the sun to calibrate these things? I guess this can be expanded to sundials as well.

I guess, because it is all relative, how can anyone know exactly when the Solstice happens when it is dark?


It's noon somewhere on the planet when a solstice happens, also while a solstice can be identified by a specific time by equations and computers now. In ancient days it was more a period of time refering to the sun standing still. In fact the secular celebration of Christmas being on December 25th is when our ancestors first noticed the sun starting to inch up higher 3-4 days after the solstice and they celebrated the daylight coming back. If you were at Stonehenge from June 18th to 25th the light would probably have basically the same phenomenon on the solstice as the sun will rise essentially in the same place (perhaps a degree off)

If you go to timeanddate.com and look at the sunset and sunrise for wherever you live if you look at the change in daylight length from day to day it gets less at less at gradually approaches 0 and then slowly moves in the other direction and the lengthening and shortening of days are the most extreme at the equinoxes in March and September.
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frmrCapCadet
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Re: Solstice Questions

Fri May 15, 2020 2:53 pm

Another odd thing is that while Winter Solstice is about the 22nd of December, the sun rise and sun set are not symmetrical, i.e., sun rises a little later, but sets late enough so that the day is still getting longer (or the other way around). Anyone have a 100 word or less explanation?
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StarAC17
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Re: Solstice Questions

Fri May 15, 2020 3:28 pm

frmrCapCadet wrote:
Another odd thing is that while Winter Solstice is about the 22nd of December, the sun rise and sun set are not symmetrical, i.e., sun rises a little later, but sets late enough so that the day is still getting longer (or the other way around). Anyone have a 100 word or less explanation?


I'll try to explain this the best I can.

In the case of the winter solstice the earliest sunset occurs around December 7th mid latitudes and the latest sunrise about January 3rd or 4th.
In the summer solstice the earliest sunrise in around June 7th and the latest sunset about July 3rd or 4th.

This is because solar noon is not at the same time every day and around both solstices it is getting later relative to the 24 hour clock that we use. A true day is one noon to the next but using our clock it is always 24 hours. This is remarkably precise but not perfect because the orbit of earth is elliptical and due to the axial tilt this can be longer or shorter than 24 hours depending on the time of the year.

https://www.timeanddate.com/astronomy/e ... -time.html
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frmrCapCadet
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Re: Solstice Questions

Fri May 15, 2020 9:07 pm

Star - good explanation, I am not into the complexity of the math involved with ellipses and tilts but can intuit the complexity they entail. Here is a second question. When I look at a quarter moon, intuitively it seems as though a line perpendicular to the line connecting the two horns (and at its midpoint) should point to the sun. Obviously it does not. Someone once told me it was too complicated for him to explain. Can you enlighten me, the sun and moon cannot. LOL
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StarAC17
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Re: Solstice Questions

Fri May 15, 2020 10:02 pm

frmrCapCadet wrote:
Star - good explanation, I am not into the complexity of the math involved with ellipses and tilts but can intuit the complexity they entail. Here is a second question. When I look at a quarter moon, intuitively it seems as though a line perpendicular to the line connecting the two horns (and at its midpoint) should point to the sun. Obviously it does not. Someone once told me it was too complicated for him to explain. Can you enlighten me, the sun and moon cannot. LOL


Are you referring to when a quarter moon and the sun are in the sky at the same time that the half the visible moon does not point at the sun as you see it in the sky? I am going to assume yes and I will explain as best I can without any math.

So the line connecting the two horns is the moon's terminator and in reality it is always a straight line, it appears as curved because you are looking at a sphere and not a disc.

When you look at the moon from your perspective you have to consider your latitude on a globe and the position of the you on earth looking at the moon the observation which is why that line's direction will change from your perspective as the earth rotates throughout the time a quarter moon is above the horizon as will a gibbous moon or a crescent one.

A first quarter moon rises at Noon to sets at midnight and a 3rd quarter moon is the opposite, on average. (An interesting note the first quarter moon is highest in the sky at the spring equinox and the last quarter moon is high at the fall equinox therefore in the sky longer. The new moon is the highest at the summer solstice and the full moon is highest at the winter solstice.)

At the first quarter phases the moon you are looking at the illuminated half pointing in the direction of the sun as seen from space. In the event of the first quarter the moon transits from its lunar morning to afternoon at or around sunset. Lunar morning being in the eastern half of the sky and afternoon being in the western half of the sky. When lunar noon is reached the moon is pointing at the direction of the sunset or sunrise and the terminator is vertical from your perspective and that perpendicular line points west. All of this is opposite for 3rd quarter moon.

If you were to take a series of pictures of a first quarter moon and lined them up you would see that there would be no change to what is illuminated throughout that lunar day. Your perspective changes regardless of where you are on the planet.

I would look at it in from the 3D scale the sun is very big and far away and the illuminated part of the moon always points at the sun.

Here are some links:

https://www.timeanddate.com/astronomy/m ... ation.html

Videos on the moon phases, one easy experiment and one clear explanation.

https://www.youtube.com/watch?v=wz01pTvuMa0 (If you have bored kids, do this with them)

https://www.youtube.com/watch?v=AQ5vty8f9Xc
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frmrCapCadet
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Re: Solstice Questions

Tue May 19, 2020 9:09 pm

Hey Star - thanks. I haven't followed the links yet, but I realize I was thinking flat earth/naive realism (I'm a philosophy major). Your last comment wised me up. The Sun is not behind the earth, the moon is small enough and close enough to be almost behind the earth, not the sun.
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