Explained: Flat Earth Theory: Why don’t our clocks have to change by 12 hours in 6 months?

Alec Riz

New Member
When researching Flat Earth Theory there is 1 claim that I am finding puzzlingly hard to debunk.

If the earth is spinning around its own axis, and orbiting around the sun, at a regular speed then, why don't we have to change our clocks by a full 12 hours every 6 months to account for the fact that we are on opposite sides of the sun.

For example - 2pm on Summer Solstice should be middle of the day which follows that if we are on the opposite side of the sun with both orbit and spin of the earth being consistent then 2pm on Winter solstice should be the middle of the night, but in actuality we only need to adjust our clocks by one hour.

Is there an obvious reason for this that I am missing??

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Mick West

Staff member
Because the daily difference caused by the orbit around the sun is included in the 24 hours.

Belfrey

Senior Member.
For example - 2pm on Summer Solstice should be middle of the day which follows that if we are on the opposite side of the sun with both orbit and spin of the earth being consistent then 2pm on Winter solstice should be the middle of the night, but in actuality we only need to adjust our clocks by one hour.
We actually don't need to adjust our clocks at all. Solar noon is still solar noon. Daylight savings time doesn't correct the time to match solar noon, it offsets our time by an hour for reasons having nothing to do with "correction." https://en.wikipedia.org/wiki/Daylight_saving_time

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Hevach

Senior Member.
We actually do have to. We just built it into the units of measurement so the clock does it for us.

There's two types of day.

A Siderial day is the time it takes a point on the Earth to traverse an arbitrary point at infinity (we use the First Point of Ares for this, but realistically we could chose any point we desire for the same result), and is always 23:56:04.1.

A Solar day (the one we're familiar with in day to day life) is the time it takes a point on the Earth to traverse the location of the sun, and averages 24:00:00, but because orbital speed is not constant actually varies by almost 30 seconds either way.

Now, if we were to set a clock by Siderial time, then we would have to readjust it every day to keep noon aligned with the sun, because the sun is no longer at the same celestial coordinates the clock was aligned to yesterday.

However, because that progression is very similar every day, with a maximum variation of only a minute, we can select units of measuring time that actually build the average adjustment into the clock every day and live with the 30 second back-and-forth drift of noon (which aligns with seasonal changes and is so vastly smaller than seasonal changes anyway that it doesn't matter).

Now, technically, that's not what we did. We chose our units a long time ago based on the Solar day to begin with, and never gave a second thought to the Sideral day. A number of civilizations knew the Siderial day was a thing, but actually using it or tracking it is of minimal use to a civilization without astronomical instruments of a precision that didn't exist until the 19th Century.

Trailblazer

Moderator
Staff member
Exactly what @Hevach said. The difference between a sidereal day and a solar day is approximately 3 minutes 56 seconds, or 236 seconds.

Six months as measured by us on Earth is 182.5 solar days (ignoring leap years), so our clocks are actually lagging the sidereal day by:

236 seconds/day x 182.5 days = 43070 seconds, or 11 hours 57 minutes 50 seconds.

So, after six months, we have already automatically adjusted our clocks by almost exactly 12 hours.

Edit: I was pondering why this didn't add up to exactly 12 hours, and it's because the Earth actually rotates 366 times on its axis during the year, not 365 times. (It's actually 366.2425 times.) We count 365 days, because the Earth's orbit means that the sun has (from our viewpoint) also circled the globe in the opposite direction, cancelling out one day.

If you multiply the exact time difference (solar day minus sidereal day) of 235.9084 seconds by 366.2425 days, you get exactly 86,400 seconds or 1 day.

There's a good explanation here

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Alec Riz

New Member
Thanks for the answer! I knew there must be a simple explanation.

arkantuspc

New Member
Exactly what @Hevach said. The difference between a sidereal day and a solar day is approximately 3 minutes 56 seconds, or 236 seconds.

Six months as measured by us on Earth is 182.5 solar days (ignoring leap years), so our clocks are actually lagging the sidereal day by:

236 seconds/day x 182.5 days = 43070 seconds, or 11 hours 57 minutes 50 seconds.

So, after six months, we have already automatically adjusted our clocks by almost exactly 12 hours.

Edit: I was pondering why this didn't add up to exactly 12 hours, and it's because the Earth actually rotates 366 times on its axis during the year, not 365 times. (It's actually 366.2425 times.) We count 365 days, because the Earth's orbit means that the sun has (from our viewpoint) also circled the globe in the opposite direction, cancelling out one day.

If you multiply the exact time difference (solar day minus sidereal day) of 235.9084 seconds by 366.2425 days, you get exactly 86,400 seconds or 1 day.

There's a good explanation here

This just make sense if you think in a 6 months base. If you think in a 3 and 9 month then the math doesn't work.

I mean... After 3 months there will be a delay

236 seconds/day x 91,25 days = 21535 seconds, or 5 hours 58 minutes.

For example:

Avon Park, Florida

January 2016 - 1st

Sunrise: 7:16am
Sunset: 5:42pm

March 1st

Sunrise: 6:50am >>>> here sun position should be almost ahead us (7:16 am + 6 hr = 01:16pm) or completely dark (7:16am - 6 hr = 1:16 a.m)
Sunset: 6:26pm <<<<

June 1st

Sunrise: 6:31am >>> "ok", 12 hours diference
Sunset: 8:17pm

Sep 1st

Sunrise: 7:05am > Again, not ok.
Sunset: 7:47pm

dec 1st

Sunrise: 6:59am > back to point one
Sunset: 5:31pm

So, I'm not sure this is a solved problem.

Mick West

Staff member
So, I'm not sure this is a solved problem.

You seem to be adding the adjustment to the solar days (which are 24 hours long), when it's actually the adjustment you add to convert a sidereal time (just earth's axial rotation) to solar time (axial plus solar orbital).

Z.W. Wolf

Senior Member.
It's not clear to me what your reasoning is. First, you're making a mistake by looking at sunrise and sunset as there is a confounding variable - the axial tilt. You should be looking at solar noon versus the stars at the meridian. In other words the time at which the sun hits the meridian versus when a certain point on the celestial sphere hits the meridian. They aren't in phase. The stars and sun move at a different speed across the sky.

So tell me: Does the sun lag behind the celestial sphere or does the celestial sphere lag behind the sun?

This is the basis of astrology, by the way. The sun is "in" different constellations during the year. And more importantly to an amateur astronomer, there are different constellations up during the night. Summer here in the northern hemisphere is when we get Scorpius and Sagittarius up in the middle of the night. (important to me anyway because that's the direction toward the center of our galaxy and rich in interesting stuff.) But we can't see Scorpius or Sagittarius at all in December. Why?

It's best to picture the physical cause of this. It's simply because there are two movements: The earth orbiting the sun and the earth rotating on its axis. If you fixed a ball on a bicycle tire and spun the tire around once, the ball would also make one rotation on its axis. The "orbit" of the ball adds one rotation of the ball.

But the earth is not fixed on a rim. And it does not do the equivalent: one side of the earth does not eternally face the sun. The earth has a second motion. It's rotation. Is this important?

So tell me... picture it yourself... does the earth's orbit in one sidereal year add one rotation of the earth or take one away, or do nothing?

This is so much more understandable if you do a physical demonstration for yourself rather than just trying to picture it.

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Hama Neggs

Senior Member.

Solar noon takes longer to come around each day due to Earth's orbit. A sidereal day is shorter than a solar day.

Hofnarr

Member
This question got me stumbeling once. Took me a while to picture whats going on, but the answer is plain simple and already stated here: our 24hour day is already linked to the sun and earths orbit around it. took me a while..
[...]

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Gundersen

Senior Member.
This YT clip from Vsauce talks about sideral day, solar day, analemma and equation of time. Jump to 5:30.

I was just going to post that, saw it the other day, really informative.

Trailblazer

Moderator
Staff member
This just make sense if you think in a 6 months base. If you think in a 3 and 9 month then the math doesn't work...
I'm not quite sure what you are doing with your calculations. Sunrise and sunset times are given in solar time, so the adjustment due to the Earth's progression around its orbit is already factored in. Sunrise gets earlier and sunset gets later in summer compared to winter, but this is nothing to do with sidereal time vs solar time. Noon is still noon, and sunrise and sunset vary roughly symmetrically either side of noon.

The original question asked why a given clock time, say 2pm, isn't in the middle of the night for part of the year when we are on the "other side" of the orbit. The answer is simply that we use solar time to run our clocks, and solar time is defined so that it keeps in step with yhe Earth's rotation relative to the sun, not relative to the stars.

If we set our clocks to sidereal time, rather than solar time, then we would find that after 3 months the sun was overhead at 6pm rather than noon. After 6 months it would be overhead at midnight. After 9 months it would be overhead at 6am. And after 12 months it would be overhead at noon again. (And, incidentally, we would find that approximately 366.24 days had passed between solstices, not 365.24!)

John T. Banewicz

New Member
My observation: Earth rotates 365.2425 solar, or calendar days a year about its axis plus 1 sidereal, or orbital day about the sun. A solar day uses the sun, or observer at the center of orbit as its reference point; a sidereal day a star, or distant observer reference point. These are two different frames of reference. It's like observing a horse race from the center of the oval track as opposed to the bleachers. The observer at the center (sun) only sees one side of the horses and concludes that they are rotating about the center of the track but not their axis. The guy in the bleachers (star) watching the same race sees all four sides and concludes that the horses are indeed rotating about their axis while orbiting the track. The distant observer must subtract one rotation per orbit to determine the actual number of axial rotations: 365.2425 solar calendar days / year vs. 366.2425 sidereal days.

An axis is an imaginary axle. A real axle is always attached to something: either the center of orbit (sun) or something external to its orbit. If attached to the center (sun) by gravity, a point on the axis facing the center of orbit is always perpendicular to the direction of motion (orbit). With any number of rotations per orbit, the opposite side of the mounted object always faces the center every 180 degrees. In other words, noon in March should be midnight in September, but that is not what we experience.

If observed externally (star) from a stationary spot in the bleachers, Earth's axis appears to be rotating CCW for 180 degrees of orbit then CW for the next 180 degrees while Earth returns to its same starting point facing the sun every ~24 hours. Both the axis and Earth appear to be rotating from the star's perspective. However, if physically connected to the star (observer), the force on the earth would necessarily be constantly changing strength to maintain a near circular orbit. The star would be moving with the force. Imagine how gears on a mechanical clock function. Because the star is a stationary observation point; not the source of external connection, the axis actually continually faces the same direction and only appears to be rotating. If the star was the source connection, it would be moving with the changing force on the earth.

Like the guy in the bleachers that sees the right side of the horse at the starting gate (0 degrees) then the left side of the horse 180 degrees later, the star sees the same thing. From either the sun's or the star's frame of reference, the opposite side of a rotating object mounted on the axle faces the center every 180 degrees. In other words, noon in March should be midnight in September, unless of course, the axis is virtual and only real in the mind of the believer.

Gundersen

Senior Member.
An axis is an imaginary axle. A real axle is always attached to something: either the center of orbit (sun) or something external to its orbit. If attached to the center (sun) by gravity, a point on the axis facing the center of orbit is always perpendicular to the direction of motion (orbit). With any number of rotations per orbit, the opposite side of the mounted object always faces the center every 180 degrees. In other words, noon in March should be midnight in September, but that is not what we experience.

During a solar-, or calendar-, day will the earth rotate more than 360 degrees. During a sidereal-day, the earth rotates quite close to 360 degrees.

...the force on the earth would necessarily be constantly changing strength to maintain a near circular orbit.

The earths orbit is actually not circular. That is why that the length of a solar day actually changes during the year, but evens out to quite close to 24 hours over a year.

You are in your calculations assuming that 1 day will equal 360 degrees rotation which is is not. it always rotates more than that.

I know it is quite confusing, but really, watch the video posted by Raymond.

Henk001

Senior Member.
John, let me give it a try: To put it really simple, considering the star background as stationary (and for the course of a year -- even centuries -- it doesn't change notably), then the earth's rotation period is 23h56m04s. That is to say, after that period you see the same star in the same direction. On top of this the earth also orbits the sun in a year. Now we defined our calendar day, being a period of 24h, with respect to the sun. Those 24 h have past when you see the sun in the same direction. Obviously that takes a bit longer than the real rotation period. After every 360° rotation of 23h56m04s Earth has to rotate a little bit further before an observer sees the sun again in -- say -- the south, at noon. On average, that extra time is 3m56s.
Vsauce with his beautiful video goes into a lot of detailed abberations of this simplified picture, but basically this is all there is. Earth rotates 366.2422 times around its axis every year (366.2422 siderial days) and in doing so, combined with its yearly path around the sun, we see the sun appear 365.2422 times in the same direction, reducing our calendar year to 365 (+0.2422) solar days -- which cannot be identified as 360° rotations.

Your "rotating axis" is obscure to me, so I find it rather difficult to go into that subject (can you perhaps provide an explaining picture of what you mean?).

One thing might help finally. There is also some kind of siderial "noon". 12h sidereal time. This indeed changes in the course of a year: at the time of the spring equinox 12h sidereal time is in the middle of the night; at the fall equinox 12h sidereal time is at solar noon.

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John T. Banewicz

New Member
I do my research in my laboratory (kitchen table) with sophisticated pieces of highly sensitive scientific equipment (lazy Susan, salt shaker, a cup, and a soda top with the straw through the center). From my sidereal distant observer frame of reference (kitchen chair) when I orbit the axis (straw) continually facing in the same direction from the zero degree position CCW, it appears to be rotating CCW for 90 degrees, then CW for 180 degrees, then CCW for the last 90 degrees. While orbiting the axis continually facing in the same direction, my hand moves in a curve first up and to the right, then up and to the left, then down and to the left, then down and to the right to the starting point. My sidereal frame of reference (chair) is stationary while an external changing force (my arm) moves the axis in its orbit.

From my kitchen chair sidereal frame of reference I see all sides of my coffee cup with each rotation of the LS (one sidereal rotation per orbit). However, from my solar day center observer frame of reference (center of the LS), I only see one side of the cup. The cup is rotating about the center of the LS but not about its axis.

I place my cup on the edge of the LS with the handle facing the center, rotate CCW the cup 90 degrees then the LS 90 degrees. I do this four times. At 180 degrees, the handle is always pointing away from me no matter how many times I rotate the cup in one orbit (year).

Mick West

Staff member
I place my cup on the edge of the LS with the handle facing the center, rotate CCW the cup 90 degrees then the LS 90 degrees. I do this four times. At 180 degrees, the handle is always pointing away from me no matter how many times I rotate the cup in one orbit (year).
What if you rotate it 365.25 times per year?

Henk001

Senior Member.
I do my research in my laboratory (kitchen table) with sophisticated pieces of highly sensitive scientific equipment (lazy Susan, salt shaker, a cup, and a soda top with the straw through the center). From my sidereal distant observer frame of reference (kitchen chair) when I orbit the axis (straw) continually facing in the same direction from the zero degree position CCW, it appears to be rotating CCW for 90 degrees, then CW for 180 degrees, then CCW for the last 90 degrees. While orbiting the axis continually facing in the same direction, my hand moves in a curve first up and to the right, then up and to the left, then down and to the left, then down and to the right to the starting point. My sidereal frame of reference (chair) is stationary while an external changing force (my arm) moves the axis in its orbit.

From my kitchen chair sidereal frame of reference I see all sides of my coffee cup with each rotation of the LS (one sidereal rotation per orbit). However, from my solar day center observer frame of reference (center of the LS), I only see one side of the cup. The cup is rotating about the center of the LS but not about its axis.

I place my cup on the edge of the LS with the handle facing the center, rotate CCW the cup 90 degrees then the LS 90 degrees. I do this four times. At 180 degrees, the handle is always pointing away from me no matter how many times I rotate the cup in one orbit (year).
That didn't help very much. But I won't give up. It could be English not being my mother language, but what do you mean by "I orbit the axis"? What is continually facing in the same direction -- you or the axis? Is the soda top on top of the lazy susan? In the middle of it, or on the edge? What does it represent: The earth? What does the coffee cup represent?

Henk001

Senior Member.

with a picture I mean sth like this.

Trailblazer

Moderator
Staff member
In other words, noon in March should be midnight in September, unless of course, the axis is virtual and only real in the mind of the believer.
It would be, if we used sidereal time. But we don't, we use solar time, which is DEFINED BY the sun being overhead at noon. Which is why noon is always noon (give or take minor variations, time zone quirks, daylight saving time etc etc).

John T. Banewicz

New Member
What if you rotate it 365.25 times per year?
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I didn't consider fractional rotations. Thanks for making me reconsider my conclusions. I stand corrected: noon in March should be noon in September with a 365.25 day solar year with Earth orbiting the sun.

I became interested in astronomy several years ago after reading Emanuel Velikovsky's “Worlds in Collision” which documents evidence that there was originally a 360 day solar year and all areas of Earth changed their calendars at approximately the same time to accommodate an additional ~5 days. My original assumption and calculations were based on a 360 day year with only additional whole days added.

Implications of a 360 day solar year are perfectly circular celestial orbits with exactly 30 day lunar months marked by the phases of the moon and exactly 90 day seasons. Velikovsky believed Earth orbited the sun, but another implication he didn't consider, is that noon in March would be midnight in September with a 360 day solar year. Also, with circular orbits, solstices don't occur; only eternal equinoxes so what would determine a change from one season to the next and the end of the old year and beginning of the new?

I suspect the sun originally orbited a stationary Earth. Seasons were marked by the sun traveling in its orbit vertically from the tropic of Capricorn to the tropic of Cancer and returning. One complete cycle was a year. Noon in March would be noon in September

For hundreds of years after the length of the solar year changed, astronomers continued to believe in perfectly circular celestial orbits. I believe a 360 day year is the reason we have 360 degrees in a circle and 12 numbers (months) on a clock. Each quarter of a clock represents a season. A thousand years from now archeologists will claim that we worshiped the sun and moon because of our calendars (movement of the sun) and moon dials (clocks) hanging on our walls and wrists.

Auldy

Senior Member.
A thousand years from now archeologists will claim that we worshiped the sun and moon because of our calendars (movement of the sun) and moon dials (clocks) hanging on our walls and wrists.

Considering the Julian calendar is already over 2000 years old, and we understand why it exists and how it works, I have faith that future historians will be able to understand as well.

Spectrar Ghost

Senior Member.
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I didn't consider fractional rotations. Thanks for making me reconsider my conclusions. I stand corrected: noon in March should be noon in September with a 365.25 day solar year with Earth orbiting the sun.

I became interested in astronomy several years ago after reading Emanuel Velikovsky's “Worlds in Collision” which documents evidence that there was originally a 360 day solar year and all areas of Earth changed their calendars at approximately the same time to accommodate an additional ~5 days. My original assumption and calculations were based on a 360 day year with only additional whole days added.

Implications of a 360 day solar year are perfectly circular celestial orbits with exactly 30 day lunar months marked by the phases of the moon and exactly 90 day seasons. Velikovsky believed Earth orbited the sun, but another implication he didn't consider, is that noon in March would be midnight in September with a 360 day solar year. Also, with circular orbits, solstices don't occur; only eternal equinoxes so what would determine a change from one season to the next and the end of the old year and beginning of the new?

I suspect the sun originally orbited a stationary Earth. Seasons were marked by the sun traveling in its orbit vertically from the tropic of Capricorn to the tropic of Cancer and returning. One complete cycle was a year. Noon in March would be noon in September

For hundreds of years after the length of the solar year changed, astronomers continued to believe in perfectly circular celestial orbits. I believe a 360 day year is the reason we have 360 degrees in a circle and 12 numbers (months) on a clock. Each quarter of a clock represents a season. A thousand years from now archeologists will claim that we worshiped the sun and moon because of our calendars (movement of the sun) and moon dials (clocks) hanging on our walls and wrists.

Worlds in Collision was recognized as claptrap immediately - MacMillan took such heat for it's publication they sold the rights within months of it's release in 1950.

You need to look at more realistic astronomy; there is simply no way that a geocentric solar system could naturally form, let alone transition to a heliocentric system.

BTW, 60 and 360 are great divisors because of the large number of factors they have. 60 is divisible by all numbers up to 6, as well as ten. 360 is also divisible by 8 and 9. They were chosen to make the math easier. The closeness of 360 to the days in a year is coincidence.

Henk001

Senior Member.
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Also, with circular orbits, solstices don't occur; only eternal equinoxes so what would determine a change from one season to the next and the end of the old year and beginning of the new?
Solstices and seasons occur because of the tilted rotation axis with respect to the orbital plane, not because of the elliptical shape of the earth's orbit.
For hundreds of years after the length of the solar year changed, astronomers continued to believe in perfectly circular celestial orbits. I believe a 360 day year is the reason we have 360 degrees in a circle and 12 numbers (months) on a clock. Each quarter of a clock represents a season. A thousand years from now archeologists will claim that we worshiped the sun and moon because of our calendars (movement of the sun) and moon dials (clocks) hanging on our walls and wrists.
The perfect circular shape was one of the ideas of Plato. It was a metaphysical standpoint, that gradually eroded because observations not quite matched this ideal form. In Ptolemy's Almagest we find -- although still circles -- already excentric orbits, epicycles and equants. Kepler needed a ten year mathemathical wrestling with Tycho Brahe's observations to finally abandon the Platonian circle-idea and reluctantly conclude the orbits had to be ellipses.

The use of numbers like 12, 60 and 360 as units comes from the time of the first calculation methods without the use of fractions. Because of them being great dividers as Spectrar Ghost pointed out. (12: 1,2,3,4,6 // 60: 1,2,3,4,5,6,10,12,15,20,30). There has been speculated that the use of 360° for a full circle comes from 360 being a multiple of 60 and thus being a "round" number (in the sexagesimal system) close to the number of days in the year.
Which never has been 360 by the way. Velikovsky, (like others as Sitchin), never took the trouble to make physical calculations about the possiblity of his planetary billiard game. If he had, he never would have published it...

John T. Banewicz

New Member
Your "rotating axis" is obscure to me, so I find it rather difficult to go into that subject (can you perhaps provide an explaining picture of what you mean?).

Put your finger (axis) on the edge of a Lazy Susan (orbit) and rotate CCW with your fingernail always facing the same direction; east for example. From the stationary 0 degree frame of reference (your chair) you will see a little more of your finger, so it appears to be rotating. However, an axle does not rotate. Notice what your arm is doing. This is an example of an axle externally attached to something. This is how astronomy maintains Earth's axis functions.

If the non-rotating but orbiting axis is attached to the center, a point on the axle facing the direction of motion is always perpendicular to the center.

John T. Banewicz

New Member
That didn't help very much. But I won't give up. It could be English not being my mother language, but what do you mean by "I orbit the axis"? What is continually facing in the same direction -- you or the axis? Is the soda top on top of the lazy susan? In the middle of it, or on the edge? What does it represent: The earth? What does the coffee cup represent?

"I orbit the axis"? I move the axis into a circular motion. The axis is always facing the same direction: east for example. I am a stationary distant observer. I use the soda top and straw to simulate Earth mounted on an axis. I didn't mention how I use them. I place a mark on both and observe how they behave when I rotate and put them in orbit. I use the handle of the coffee cup on the Lazy Susan to illustrate how a point on Earth moves as it orbits the sun. Imagine the handle as noon or midnight.

John T. Banewicz

New Member
Worlds in Collision was recognized as claptrap immediately - MacMillan took such heat for it's publication they sold the rights within months of it's release in 1950.

MacMillan made a grave financial error in 1950. I have a used copy of DoubleDay's 23rd printing. I paid \$30 for a book that originally sold for \$10. I saw a new paperback edition in Barnes and Noble for \$30. The book is still in printing after 66 years. There are also "Electric Universe" websites that he inspired.

John T. Banewicz

New Member
Solstices and seasons occur because of the tilted rotation axis with respect to the orbital plane, not because of the elliptical shape of the earth's orbit.
I stand corrected. However, I have an issue with an axis (axle) always facing the same direction. The velocity of the mounted object is constantly changing to face the center at the same time every day. In other words, the rotation velocity of Earth at the equator is constantly increasing and decreasing for noon to occur at the same time.

Spectrar Ghost

Senior Member.
I stand corrected. However, I have an issue with an axis (axle) always facing the same direction. The velocity of the mounted object is constantly changing to face the center at the same time every day. In other words, the rotation velocity of Earth at the equator is constantly increasing and decreasing for noon to occur at the same time.

I don't understand what you're getting at. Noon is defined by the sun being at it's highest point in the sky. There's no change in rotational velocity needed for the sun to be at it's highest point at noon. There are some very small changes in the length of a solar day over the year, due to the earth's elliptical orbit and the changes in orbital velocity associated with it, but they're not enough to be noticeable.

Henk001

Senior Member.
I stand corrected. However, I have an issue with an axis (axle) always facing the same direction. The velocity of the mounted object is constantly changing to face the center at the same time every day. In other words, the rotation velocity of Earth at the equator is constantly increasing and decreasing for noon to occur at the same time.
"The earth axis always faces the same direction" is perhaps the way this is formulated; a way I am not really happy with. I'd rather say that the axis always has the same orientation, pointing in the same direction: when you stand at the geographical north pole (and the rotation axis goes right through you) you will see the pole star (Polaris) straight above your head, all year round. It has nothing to do with facing east or west of the rotating earth.

John T. Banewicz

New Member
I don't understand what you're getting at. Noon is defined by the sun being at it's highest point in the sky. There's no change in rotational velocity needed for the sun to be at it's highest point at noon. There are some very small changes in the length of a solar day over the year, due to the earth's elliptical orbit and the changes in orbital velocity associated with it, but they're not enough to be noticeable.
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A point on the edge of a spinning lazy susan is always facing the direction of motion which is perpendicular to the center. The point is the axis, or axle, the lazy susan is gravity connecting the point to the sun (salt shaker) in the center. The outside edge of the lazy susan is Earth's orbit. An object (Earth) mounted on this axis would have a constant rotational velocity to return to its starting point. In other words, noon would be noon the same time every day.

“...only a circle can bring a body back to its original position, while a real inequality of motion could only be caused by a change in the motive power or by a variation in the body moved, both of which assumptions are absurd.” “A History of Astronomy From Thales to Kepler” by J.L.E. Dreyer Page 322

In the above scenario we have a circular orbit and circular rotation with Earth returning to its original position on an axis attached to the sun through gravity.

Kepler proposed a tilted axis that continually faced the same direction (east for example) as it orbited the sun. Hold a tilted pencil firmly on the edge of a lazy susan spinning CCW. To keep the pencil always facing east you have to rotate the pencil CW for 90 degrees, CCW for 180 degrees, then CW for the remaining 90 degrees. To return to its original position, the object mounted on this axis would have to “change … [its] motive power” "which ... [is] absurd". Also, there is now a force other than gravity (lazy susan) causing the axis to rotate: your arm, which is an external force. The axis is no longer attached to the sun through gravity: it's attached to some external force.

John T. Banewicz

New Member
"The earth axis always faces the same direction" is perhaps the way this is formulated; a way I am not really happy with. I'd rather say that the axis always has the same orientation, pointing in the same direction: when you stand at the geographical north pole (and the rotation axis goes right through you) you will see the pole star (Polaris) straight above your head, all year round. It has nothing to do with facing east or west of the rotating earth.
Look closely at your posted diagram. Is Polaris moving with Earth's axis in its orbit, or is it stationary?

scombrid

Senior Member.
In other words, the rotation velocity of Earth at the equator is constantly increasing and decreasing for noon to occur at the same time.

We move the time that we call noon a little bit every day.

Henk001

Senior Member.
Look closely at your posted diagram. Is Polaris moving with Earth's axis in its orbit, or is it stationary?
Polaris is (as good as) stationary. It is 433 lightyears away. That is more than 27,000,000 x the distance earth-sun. Therefore in this graphic you can't distinguish the tiny angle that in fact should be between those arrows pointing at Polaris. Or to put it differently. Those arrows are (as good as) parallel. Parallel lines intersect at infinity and 433 lightyears is as good as infinitely far away as compared with the distance earth-sun.
That tiny angle is measurable by the way. It is called the parallax and for Polaris this angle is 0.00745" (arcseconds). (In fact that's where we got its distance from.) Polaris -- like may other "nearby" stars -- seems to make a yearly ellipse, only visible through a strong telescope, with a diameter of that 0.00745" which is in fact a projection of the earths yearly orbit around the sun. This is but one example of observational evidence for the movement of the earth.

Spectrar Ghost

Senior Member.
P { margin-bottom: 0.08in; }

A point on the edge of a spinning lazy susan is always facing the direction of motion which is perpendicular to the center. The point is the axis, or axle, the lazy susan is gravity connecting the point to the sun (salt shaker) in the center. The outside edge of the lazy susan is Earth's orbit. An object (Earth) mounted on this axis would have a constant rotational velocity to return to its starting point. In other words, noon would be noon the same time every day.

“...only a circle can bring a body back to its original position, while a real inequality of motion could only be caused by a change in the motive power or by a variation in the body moved, both of which assumptions are absurd.” “A History of Astronomy From Thales to Kepler” by J.L.E. Dreyer Page 322

In the above scenario we have a circular orbit and circular rotation with Earth returning to its original position on an axis attached to the sun through gravity.

Kepler proposed a tilted axis that continually faced the same direction (east for example) as it orbited the sun. Hold a tilted pencil firmly on the edge of a lazy susan spinning CCW. To keep the pencil always facing east you have to rotate the pencil CW for 90 degrees, CCW for 180 degrees, then CW for the remaining 90 degrees. To return to its original position, the object mounted on this axis would have to “change … [its] motive power” "which ... [is] absurd". Also, there is now a force other than gravity (lazy susan) causing the axis to rotate: your arm, which is an external force. The axis is no longer attached to the sun through gravity: it's attached to some external force.

Now replace your point on the edge with a top, spinning at constant speed. A point on the top will experience solar noon after a full rotation, plus or minus a little based on how far it orbited in that time. However, with a circular orbit this adjustment will be the same for each day.

An elliptical orbit sweeps out the same area around the focus per time, so the velocity changes and the length of a solar day varies slightly as well.

https://en.m.wikipedia.org/wiki/Analemma

Henk001

Senior Member.
P { margin-bottom: 0.08in; }

“...only a circle can bring a body back to its original position, while a real inequality of motion could only be caused by a change in the motive power or by a variation in the body moved, both of which assumptions are absurd.” “A History of Astronomy From Thales to Kepler” by J.L.E. Dreyer Page 322

In the above scenario we have a circular orbit and circular rotation with Earth returning to its original position on an axis attached to the sun through gravity.

This is Copernicus arguing the heavenly bodies' motions had to be uniform and circular, still trapped in Plato's dogma. His argumentation on this is flawed as Kepler showed through his first and second law. Both Copernicus and Kepler by the way were still thinking in the Aristotelian way that a movement needed a motive force, where Newton's first law showed this to be untrue.

The axis is not attached to anything. It is the gravitational attraction between the masses that delivers the necessary centripetal force to maintain circular movement. If earth were not rotating there would be no rotational axis at all, but she could still orbit the sun.

Kepler proposed a tilted axis that continually faced the same direction (east for example) as it orbited the sun. Hold a tilted pencil firmly on the edge of a lazy susan spinning CCW. To keep the pencil always facing east you have to rotate the pencil CW for 90 degrees, CCW for 180 degrees, then CW for the remaining 90 degrees. To return to its original position, the object mounted on this axis would have to “change … [its] motive power” "which ... [is] absurd". Also, there is now a force other than gravity (lazy susan) causing the axis to rotate: your arm, which is an external force. The axis is no longer attached to the sun through gravity: it's attached to some external force.

Again -- the axis is not facing any particular direction. It is a mathematical line around which the earth rotates. The axis itself is pointing (not facing) on one side towards the north celestial pole and on the other side towards the south celestial pole. There is no east or west "from the standpoint of the axis". As when you stand on the north pole there is only one direction you can go: south.

Hama Neggs

Senior Member.
The outside edge of the lazy susan is Earth's orbit. An object (Earth) mounted on this axis would have a constant rotational velocity to return to its starting point
Mounted on WHAT axis? The edge of a lazy susan is not an axis.

Hold a tilted pencil firmly on the edge of a lazy susan spinning CCW. To keep the pencil always facing east you have to rotate the pencil CW for 90 degrees, CCW for 180 degrees, then CW for the remaining 90 degrees.

I can make no sense out of what you're saying. The only way for an orbiting body to remain "facing" the same way is if it has no rotation. Of course we have to specify rotation relative to WHAT.

Also, there is now a force other than gravity (lazy susan) causing the axis to rotate: your arm, which is an external force.

Your terms are too confused. Earth's "axis" does not "rotate", Earth does. Earth AND it's axis revolve around the sun.

The axis is no longer attached to the sun through gravity: it's attached to some external force.

You're making no sense. An "axis" has no mass to be attracted by gravity from any other body.

Hevach

Senior Member.
Polaris is (as good as) stationary. It is 433 lightyears away. That is more than 27,000,000 x the distance earth-sun. Therefore in this graphic you can't distinguish the tiny angle that in fact should be between those arrows pointing at Polaris. Or to put it differently. Those arrows are (as good as) parallel. Parallel lines intersect at infinity and 433 lightyears is as good as infinitely far away as compared with the distance earth-sun.
That tiny angle is measurable by the way. It is called the parallax and for Polaris this angle is 0.00745" (arcseconds). (In fact that's where we got its distance from.) Polaris -- like may other "nearby" stars -- seems to make a yearly ellipse, only visible through a strong telescope, with a diameter of that 0.00745" which is in fact a projection of the earths yearly orbit around the sun. This is but one example of observational evidence for the movement of the earth.
To add to this, the smallest difference the human eye can distinguish is right around 0.01 degrees, or 36 arcseconds. And that's with immediate movements or closely separated objects - Polaris takes six months to move from one side to the other of its .00745 arcsecond range.

The distances to stars are mind boggling - and it's crazy to think people overestimate them even more mind bogglingly (it's almost certain every star you can see with your eyes in the sky is still burning, a very small number are likely to die "soon" and the chances that even one of them already has is almost zero). 433 ly is 27,380,000 astronomical units. Earth's orbit is two astronomical units wide.

A completely to-scale version of that diagram would have Earth at opposite solstices and Polaris at the top of the image form an equilateral triangle 2 inches wide and over 432 miles tall.

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