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Messages - Bobby Shafto

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1101
How can you post this:
Correction: The equinox does have to start at Solar Noon at some point on earth, but not necessarily your point on earth.

And then later ask this?
How then, does that reconcile with the 24 Hour Solar Day?

Solar Noon is always somewhere on earth. It will be somewhere on the point of the Equinox.  The Solar Day is based on the sun rotation around the earth - 24 hours per rotation.

How do you explain the incompatibility between Solar Day and the Number of Solar Days in a Solar Year? Where does the extra time come from?
The answer is in your correction.

1102
Correction: The equinox does have to start at Solar Noon at some point on earth, but not necessarily your point on earth.
Good edit. Does this mean you understand now where the extra time comes from?

1103
Bobby, can you provide a source on the equinox not being a point, "but a meridian"? Everything I have seen says that it is a point.
I understand how my word choice might be confusing. I just didn't want you to think that solar noon happens on a point the way equinox does.

Equinox is a point on the equator, and it's solar noon for all points along that meridian that intersects with the equator at that point. It might have been unnecessary for me to make that parenthetical but I was trying to keep clear how solar noon and equinox are related.

The difficulty I'm having is conveying to you that solar noon and equinox are the same point over the earth from equinox to equinox, 1 solar year apart. The equinox moves westward toward a new meridian where it's solar noon when the sun crosses the ecliptic (equator). It's solar noon for all of the points along that meridian but the sun is only directly overhead on the point on the equator.

1104
IT IS ALWAYS SOLAR NOON SOMEWHERE. This has nothing to do with sidereal anything.

It is always Solar Noon somewhere. Correct. But start the clock on the September Equinox point where it is 12PM Solar Noon and it will end on ~6PM after one year. Why doesn't it stop at 12PM if you are in the same position on the earth's orbit around the sun?
Because at that same location (not a point, but a meridian) at the 365th solar noon, the equinox is still ~6 hours away. The earth isn't going to stop its rotating to wait. The earth keeps turning as that meridian where the solar year began (almost) a year ago sees its local solar noon pass without the solar year ending. A little under 90° of longitude to the west, the equinox occurs and it's at that meridian's solar noon that the solar year is complete.

A little less than 90° of latitude equates a little less than a quarter of a rotation, a little less than a quarter of a day (0.24), or a little less than 6 hours.

I posted this a few hours ago.
Quote
It might help Tom to distinguish it that way.

Looking up times for the next two autumnal equinoxes, 2018 occurs 01:53 UTC on Sep 23. A year later, in 2019, it occurs 07:41 UTC.

Estimating using 15° of longitude per (solar) hour, that means that in 2018, solar noon at the time of autumnal equinox will be somewhere near 150°E meridian. But in 2019, solar noon at the time of autumnal equinox will be somewhere near the 70°E meridian. 

The 365th solar noon will have passed those on the 150° meridian because the earth hasn't reached the autumnal equinox yet. It will take another 5 hrs and 48 mins to get there. Meanwhile, the earth will keep rotating with respect to the sun and the solar noon line will keep moving west for that amount of time until...equinox.

(My meridians might be off. I'm sure there's a calculator that can figure what longitude the sun is at given UTC, but I don't have a link handy. The point ought to be made, though.)

1105
It's not a red herring. The Solar Time hour is identical to the time in our clocks and watches, and a Solar Day is 24 Solar Time hours. It relates to the sun over one day:
When "mean solar time" and "equation of time" have zero to do with understanding the "extra" 0.24 hours that you say are confounding, invoking them is a red herring. 

Those concepts matter insofar as why 0.24 hours isn't exact or why the exact value differs from year to year.

Forget that because it's not germane to comprehending the presence of the "extra time." You're either tying yourself in knots trying conflate concepts, or you're doing it intentionally to preserve a conclusion you've become invested in. I can't tell which. I want to believe you're making a sincere effort.

1106

Refer to my Equation of Time post for more on the meaning of "mean".
Red herring, Tom. Or, if not intentionally a distraction, then misunderstanding of these concepts. That's a different variance aspect (and minor compared to the 0.24 solar day shift in equinox) that you can ignore while searching for understanding the why of that 0.24 day or ~6 hr "extra time." You're off on tangents with that and precession influences.

Do you honestly want to understand? Or are you vested in debating because you are sure you've found a flaw? I'm trying to avoid debate. You act like you're trying to educate me so that I can come to your conclusion that what you're educating me about is flawed.

If you don't know why what you're referring me to is a red herring, then don't lecture me as if we're debating. I chose to engage to help you understand and resolve the conundrum you think you've identified. If you're committed to that and can't fathom that you're conflating concepts, I'm wasting my time.

1107
They are in sync. Just not by a whole number. Every 356.24 solar days per 1 solar year. That "extra time" of 0.24 solar day is the ~6 hours that is the sync.

What's the problem?

My read of your id of "the problem" is the ~6 hours as if that means solar day and solar year are not in sync. But there's no reason for synchronization to be exactly 365 solar days to 1 solar year.

Equinox to same equinox takes more time than 365 solar days. The same aspect of the earth doesn't face the sun from vernal equinox to next vernal equinox. 

1108
What?

I've long since moved past sidereal day reference frame.

1109
Solar noon is a local phenomenon. The length of the solar day is global.

It is always solar noon somewhere, so the equinox happens at solar noon for someone, just not the same person/meridian every year.

Does this help?
It might help Tom to distinguish it that way.

Looking up times for the next two autumnal equinoxes, 2018 occurs 01:53 UTC on Sep 23. A year later, in 2019, it occurs 07:41 UTC.

Estimating using 15° of longitude per (solar) hour, that means that in 2018, solar noon at the time of autumnal equinox will be somewhere near 150°E meridian. But in 2019, solar noon at the time of autumnal equinox will be somewhere near the 70°E meridian. 

The 365th solar noon will have passed those on the 150° meridian because the earth hasn't reached the autumnal equinox yet. It will take another 5 hrs and 48 mins to get there. Meanwhile, the earth will keep rotating with respect to the sun and the solar noon line will keep moving west for that amount of time until...equinox.

(My meridians might be off. I'm sure there's a calculator that can figure what longitude the sun is at given UTC, but I don't have a link handy. The point ought to be made, though.)

1110
I'm pretty sure that's it, especially since you keep referring us back to your recap. You seem to believe that the solar year can only start at solar noon. If we haven't reached the equinox by the time of the 365th solar noon, then there must be a problem because the subsequent solar year can't start except at solar noon. In other words, if you start the clock with both orbit and rotation synchronized, you think he's new cycle of the orbit must start synchronized with the rotation.

That's a fallacy.

If I'm restating your position incorrectly, tell me; in which case my question surfaces again as to why you think solar year and solar day must be synchronized in a whole number ratio. If the earth's rotation and the earth's orbit of the sun were toothed gears with a ratio of 365:1, then yeah. I'd consider it a problem if they weren't in sync after 1 cycle of the orbital gear.

But there's not. They are "synced" to a ratio of ~365.24:1 though. There's no reason I know of why that ratio exists, but they are. So at the end of 1 orbital cycle, the rotation gear will have turned a fraction more than it would have in a 365:1 ratio system.

1111
Read through the Recap post please.

After 1 Solar Year starting on the September Equinox the earth will return to the same place on the Earth-Sun orbit. The 24 Hour Solar Clock will not be in sync. This is a problem. The Sun did not change position in the Earth-Sun system. If the start point were Solar Noon, we can't have Solar Noon now + ~6 hours at the end point.
I can read it a million times and it still restates the error.

Solar year and the solar day clock not being in sync is not a problem.
If the start point of the solar year is solar noon, we CAN (and will) have the end point of that solar year ~6 hours after the last solar noon. The new solar year start point is then ~6 hours after solar noon and after another solar year, THAT endp point will be ~12 hours after the last solar noon, and so on. What you seem to want is for each new solar year to be able to start at solar noon. But that's not possible. The timing of equinox (which is how we mark the start and end of the solar year for reasons of ease of measurement) is not synchronized with the timing of solar noon (which is also an indexing convention related to ease of measurement.)

Solar days and solar years not being in sync is not the problem you think it is.
Solar year is vernal equinox to vernal equinox (or autumnal if you prefer), measuring 1 orbital cycle.
Solar day is solar noon to solar noon (or some other indexing point of the solar day if you prefer, measuring 1 rotational cycle.
There is no reason for them to be synchronized. There's no reason to believe it's a problem if they are not.
I would actually be quite fascinated by the situation if they were.

1112

You say "The earth has rotated past solar noon by the time equinox arrives."

Solar Time is based on the sun moving over the earth along a local celestial meridian. If the earth has rotated past Solar Noon after a Solar Year, then the Solar Noon has as well. The Solar Day does not fit into the Solar Year.
If by "doesn't fit" you mean there can't be a fractional solar day in a solar year, you're absolutely right. But if you do accept that a fraction of a solar day is possible, then it does "fit." 365.24 solar days fit into a solar year. The "extra time" is what makes it "fit."

Now, can you provide some "explanation...why the earth's rotation relative to the sun (solar day) must be synchronized to the orbit around the sun (solar year), without any fractional variance," else it "doesn't fit?"

1113

I have also shown with the Recap post at the top that the Solar Day must be connected to the Solar Year.


This is the crux of the issue, right here. There's no hope of resolution if we don't understand why the "solar day must be connected to the solar year" in the whole integer way you expect, or if you don't understand that the relationship is fractional.

Without that being resolved, this is a merry-go-round.
I'm getting off, unless I see an explanation from Tom why the earth's rotation relative to the sun (solar day) must be synchronized to the orbit around the sun (solar year), without any fractional variance.

1114

I have also shown with the Recap post at the top that the Solar Day must be connected to the Solar Year.


This is the crux of the issue, right here. There's no hope of resolution if we don't understand why the "solar day must be connected to the solar year" in the whole integer way you expect, or if you don't understand that the relationship is fractional.

Without that being resolved, this is a merry-go-round.

1115
Solar Noon is based on a 24 hour Solar Day. After 364.24 days Solar Noon should have moved ~6 Hours. The geometry of the scene when the earth returns to the September Equinox point shows that Solar Noon is not in that place.
Assuming solar noon was the start of the solar year, after 364.24 solar days, the last solar noon would have happened ~6 hours before the equinox. Thus, at equinox, solar noon is past. Solar noon didn't change. It still came and went as predicted.  The return to equinox after one solar year will not line up with solar noon, as you apparently expect it to. That's not the "geometry of the scene." The earth has rotated past solar noon by the time equinox arrives.

1116
I said that it can't be arbitrarily connected. Read the post again. This indicates that you are not really absorbing this content.
I wasn't addressing what you said about your own thoughts. I was addressing how you were mis-characterizing the explanations provided to you in your recap.

1117
Solar Noon can't change...Why doesn't Solar Noon move?
You started with "solar noon can't change" and then ended asking "why doesn't solar noon move?"

Solar noon is one moment out of a solar day. Solar noon doesn't care about the equinox or where the earth is in its orbit or how the ecliptic plane is oriented. As long as the earth is spinning, solar noon will come around again and again, as will any other demarcation point in the solar day. 

Even if the earth didn't orbit the sun at all but somehow just hung above the sun in one spot, you'd still have solar days if the earth is rotating making the sun appear to rise to a solar noon.

Solar noon can't change? Sure. As long as your clock is tied to the sun and the rotation of earth is constant, solar noon will be solar noon always. When the sun is at its highest elevation.

But if you tie your clock to, say, the stars? Then solar noon isn't always at the same time. It's still solar noon, but it's happening at a different sidereal time each day.

Right? But we're talking about a solar day clock, so yeah. Solar noon is constant.

So, why doesn't it move then if the solar year doesn't "match?" Why should it? Why would you expect it to? The solar year is not based on the rotation of the earth. It's based on the orbit of the earth around the sun. It's a different cyclical motion: one "inside" of the other.

They match up and are relateable fractionally, but you can have orbit without rotation and rotation without orbit (well, at least temporarily). In the sun/earth case, we have 365 and a fraction rotations for every orbit. This fraction won't change the timing of solar noon. But it will change how we relate the marking of the new solar year to the timing of a solar day.

You've got to remember your reference frames and understand the relationships between them, else you will create conundrums that don't really exist.

1118
Are you saying that the Astronomy Department at the University of Nebraska-Lincoln got Round Earth Astronomy wrong, and that you know better than them?

Their simulation is clearly showing that Solar Time is related to the Equinoxes and Solstices of the year. It is not arbitrary. The sun needs to return to its same position above the earth after 1 year.

Think of that animation like this animation of a flat earth model.
https://imgur.com/r/educationalgifs/D7aOXVA

Should I use that animation to work out things like azimuth of the sun at sunset from San Diego at the equinox?
http://oi66.tinypic.com/213iz6f.jpg
And if the azimuth of the sun is not what that animation predicts, should I reject the flat earth model?

I read you elsewhere tell someone that animation (or others like it) are visualizations. They convey the concept, but aren't intended to be accurate.

Same with that simple animation you showed that isn't synchronized to any actual time, can't be used for predicting or comparing to actual truth data (time/date) and doesn't even bother to illustrate the very aspect of the "extra time" that you are interested in. But that's because it's just a visualization. A fancy cartoon to help explain the relationship of sidereal days with solar days.

Unfortunately, it's reinforced a notion that a solar day (solar noon) must line up always with the solar year (equinox) or else something's wrong with the globe/solar model. If you are sincere in wanting to find resolution to what you see as a problem with solar noon in round earth theory, you need to break through that incorrect concept that "The sun needs to return to its same position above the earth after 1 year."

1119
The geometry of the scene shows you wrong. The time of Solar Noon when the earth returns to its position of the September Equinox can't be Solar Noon + 5+ Solar Hours. The sun and earth is in the same geometric position on the orbit. Solar Noon can't change.
Until you can discard yourself of that incorrect premise, attempting to work through it with you is bound to be fruitless.

It's disappointing that that UNL animated illustration seems to have cemented your misunderstanding. That same Astronomy Department also has published this page on the Web. Maybe it will help you get over the rigid insistence that a starting marker to the solar day must line up with the starting marker to the solar year and the end of 1 solar year.
http://astro.unl.edu/naap/motion3/sidereal_synodic.html


1120
That's not the answer to the question. That is the question I am asking. The Solar Day and the Solar Year that is based on the Equinox do not match up.
They don't match up as a whole number.  So what? I don't understand why you expect them to, especially after having it repeatedly explained why they don't.

1 solar year = 365.24 solar days.
The equinox is about 0.24 solar days later each year because they "don't match up" without the fraction. They match up well with the fraction.

We're all telling you why that is, but you keep claiming that's a problem or a question.

Furthermore, the equinox only moves at a rate measured in eons.

https://www.britannica.com/science/precession-of-the-equinoxes

Quote
Precession of the equinoxes, motion of the equinoxes along the ecliptic (the plane of Earth's orbit) caused by the cyclic precession of Earth's axis of rotation. ... Such a motion is called precession and consists of a cyclic wobbling in the orientation of Earth's axis of rotation with a period of 25,772 years.
I tried to tell you that that's a different influence on the motion, and it's much more marginal, so don't worry about it for trying to comprehend this other, much larger (relatively) variance that is the focus of your question.

Until the solar year/solar day relationship is understood, the precession affect will just add to the confusion. And it's way down in the weeds, astronomically, for the short time reference periods we've been focusing on.


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