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Ishmael
In: Toronto
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Does the lengthy side of the ellipse remain consistent year after year after year?
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DPCrisp
In: Bedfordshire
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| Galilei [designed] a system of rolling balls down an incline and letting them roll off the end of a table to see how far they would travel. As a result of this experiment he was able to derive gravity's inverse square nature. |
What, when no one else on Earth has ever experienced a gravitational field varying as the inverse square of the distance to the centre of Earth? That's bleedin' clever of him.
| This rather ridiculous notion that something the size of a planet or moon could speed up and slow down has been accepted as rote learning ever since and encoded the first mistake that subsequently led to the most famous error in science. |
Er... why ridiculous? Where do you draw the line between small enough to speed-up-and-slow-down and too big to do so?
| Nothing in the real universe travels with straight line motion. |
Agreed. So which is the curved line that we should take as neutral, the trajectory of a body with nothing going on, as against which all other motions are to be characterised as deviations? That is, having discounted the straight line, which is just a special case of a curved line.
| As the Sun moves forward the Earth is moving in the same direction as the Sun for half its orbit and against the direction of the Sun for the other half. |
The 5 million km difference between fore and aft orbital radii would be made up in 84 hours at the Sun's 16.5 km/s rate of progress towards the "Solar apex" {which is in the opposite direction to "towards the Winter Solstice", innit?}, or in 6 hours at His 220 km/s galactic orbital speed.
Assuming the numbers can be worked out for Earth and the other planets, what is the explanation for them orbiting at all?
| The Sun is travelling towards the Winter Solstice, that is why planets pass closest to the Sun at that point and are furthest away at the Summer Solstice. |
But the planets have their perihelions in all different directions.
| Planets do not speed up and slow down and any one who thinks about it logically would realise that to suggest something the size of the Moon, let alone Jupiter, could speed up and slow down is pretty ridiculous. |
In what way is this "thinking about it logically"?
| Newton had no idea what caused motion. In Principia he ascribes it to God. |
And our view is better because...? What is our view, by the way?
| They orbit at the same rate but travel different distances due to the forward motion of the Sun. |
What is this God-given constancy? Is there no force between bodies at all?
| This of course is wrong because the juggler is providing the balls with a CURRENT force. They cannot maintain their motion without the juggler's help. But according the Newton (and standard cosmology) THERE IS NO CURRENT FORCE. God put everything in motion in a straight line at the beginning of time and gravity merely changes straight line motion into orbital motion WITHOUT any need for a current force. |
This doesn't sound like any physics or cosmology I've ever heard of. How the juggler flicks his wrist or uses ping-pong paddles or anything else is irrelevant: there is always a force on the balls and, while he's not touching them, there is only one force and it determines their trajectories.
Not even God can put everything into straight line motion, since there is always a (current) force.
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Chad
In: Ramsbottom
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| DPCrisp wrote: | | Someone better gets the facts straightened out first. The way I heard it, perihelion is about January 3rd and aphelion about July 4th, making the two 'halves' about equal. |
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Ishmael
In: Toronto
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And note that the future dates are predicted using..... yup.... Newton and Kepler.
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Mick Harper
Site Admin
In: London
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Perihelion to aphelion = 180 days
Aphelion to perihelion = 185 days
The main reason for this turn-around, is that the Earth does not orbit the Sun in isolation, but as part of the Earth/Moon binary... and these figures are based on the distance from Sun to Earth... whereas Kepler's Law would require the distance from the Sun to the centre of gravity of the Earth/Moon binary to be the critical distance.
Obviously the situation will change from year to year, depending on the relative positions of the Earth and Moon. |
Even I can see this is preposterous. The incluson of such a constant force as the Moon cannot possibly lead to such an inconstant outcome. Please, somebody, come up with the correct reason.
It would be pleasingly ironic, speaking AE-ly, if true orbits turned out always to be circular after all and it was only 'this reason' that was causing perihelion being different from aphelion.
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Brian Ambrose
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Funny you should say that. I was thinking myself what a coincidence it is that the solstice-solstice time mismatch is of (about) the same magnitude as the Perihelion-aphelion mismatch.
As to the effect of the moon, remember that it means that the centre of gravity is constantly changing as earth-moon orbit the sun. Not unreasonable that this would mess up the perfect ellipse somewhat. But three days' worth? You'd think the effect would largely average out in each cycle.
Interesting (and ironic) that the future timings are predicted based on orthodox calculations - obviously someone somewhere has a perfectly Newtonian explanation.
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Komorikid
In: Gold Coast, Australia
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Ish wrote:
| Most puzzling in Komorikid's posts is this repeated reference to "planets" moving faster in one season than in another. |
Brahe assumed that the Earth was motionless. He timed the Moon's passage across the sky in the summer time. Then he did the the same in the winter time. What he found was the winter period was longer than the summer period. He then did the same with the known planets and found the same thing was happening. The planets moved faster in the summer than they do in the winter.
To understand the reason why this was happening Brahe went back to basic maths.
The simple mathematical formula he used was Time is a factor of Distance or Rate. For the time to vary, the formula required that either the distance varied or the rate varied. Brahe, who believed that the Earth was stationary at the centre of the universe, mistakenly concluded that it couldn't possibly be distance that was causing the change. That left only rate. The change in rate was causing a change in time.
The moon and the planets were speeding up in the summer and slowing down in the winter.
At the time there was no concept of aphelion or perihelion. The solstices and equinoxes occupied points on a perfect circular orbit. In fact all orbits were thought to be perfect circles.
Kepler gained access to Brahe's extensive journals when Brahe died. But even though he put the Sun stationary at the centre of the universe this didn't lead him to question Brahe rejecting distance as a reason for the change in time now that he had the Earth in motion around the Sun. He was eventually able to make elegant sense of Brahe's figures but he wasn't about to question Brahe's unfounded conclusion made on the basis of his geocentric beliefs.
This may have been due to the fact that Kepler also believed in perfect circular orbits. He struggled for years to make sense of Brahe's calculation. First using regular geometry, then nested solid geometric objects until finally he hit upon a conic section, which was a perfect ellipse.
The concept of aphelion and perihelion is a modern concept that is based on Kepler's Law. Before the 20th century the solstices were assumed to be the closest and farthest points and were determined astronomically. Aphelion and perihelion are determined mathematically.
Brahe and Kepler were timing the movement of planets across the sky. The time from winter solstice to summer solstice (183 days) and from perihelion to aphelion (184 days) is SLOWER than from the summer solstice to winter solstice (181 days) and from aphelion to perihelion (181days). This has universally been accepted as the planets speeding up and slowing down.
183/184 days is a SLOWER time than 181 days.
As you can clearly see the winter portion is of the orbit is SLOWER than the Summer just as Brahe and Kepler said. Therefore if we accept that the orbit is speeding up and slowing down as orthodoxy says, then the planet is speeding up as it moves AWAY from the closest approach to the Sun. This is exactly opposite to what Newton proposed. He said the planet speeds up towards the closest approach from which he determined it was falling towards the Sun when in fact it is falling away from the sum.
For some reason Kepler did not revisit Brahe's original assumption when he decided that the orbits were elliptical. Brahe can be forgiven for his error given his stubborn belief in a stationary Earth. To him the distance couldn't be changing. Kepler, with the Earth now in motion around the Sun should have known better.
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Komorikid
In: Gold Coast, Australia
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Dan wrote: | In what way is this "thinking about it logically"? |
You need a force to accelerate it then another force to retard it and then another force to accelerate it again on a constant basis every orbit. With a primary moving dragging its satellite along with it while that satellite is orbiting at a constant rate the same effect is produced without the need for all that accelerating and braking. Entities must not be multiplied beyond necessity.
| But the planets have their perihelions in all different directions. |
Are they. How can you tell if you are not taking direct measurements from each individual planet. All aphelions and perihelions are determined mathematically with Kepler's Law.
| Not even God can put everything into straight line motion, since there is always a (current) force. |
What current force pray-tell is keeping the Earth spinning on its axis.
I wouldn't mention your belief in a current force to any of your astrophysics friend -- they take a dim view of heretics.
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Komorikid
In: Gold Coast, Australia
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Mick wrote:
| It would be pleasingly ironic, speaking AE-ly, if true orbits turned out always to be circular after all and it was only 'this reason' that was causing perihelion being different from aphelion. |
In a way all planets are. It's only the Sun's slow movement that stretches the distance out causing them to sweep out a larger arc behind the sun than in front of it.
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Chad
In: Ramsbottom
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| Brian Ambrose wrote: | | Funny you should say that. I was thinking myself what a coincidence it is that the solstice-solstice time mismatch is of (about) the same magnitude as the Perihelion-aphelion mismatch. |
The solstice-solstice time mismatch is fixed and always in the same direction. The Perihelion-aphelion mismatch is not fixed (regardless of what Komoro keeps stating) and oscillates about a mean... sometimes Perihelion-aphelion is longer and at other times Aphelion-perihelion is longer.
(See table above... oops link seems to be broken... will fix later.)
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Chad
In: Ramsbottom
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| Komorikid wrote: | | In a way all planets are. It's only the Sun's slow movement that stretches the distance out causing them to sweep out a larger arc behind the sun than in front of it. |
Then the elliptical orbits of all the Solar planets should be aligned in the same direction... unfortunately they aren't.
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Chad
In: Ramsbottom
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| Mick Harper wrote: | | Even I can see this is preposterous. The incluson of such a constant force as the Moon cannot possibly lead to such an inconstant outcome. Please, somebody, come up with the correct reason. |
If the Moon is traveling away from the Sun just as the Earth is nearing perihelion or aphelion it can easily extend the period by a day or two (by pulling the Earth that little bit further from the Sun)... no problem.
And as Ish says, it can be predicted using the tools given to us by Newton and Kepler.
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Komorikid
In: Gold Coast, Australia
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Ish wrote:
| And note that the future dates are predicted using..... yup.... Newton and Kepler. |
By applying Kepler's Law to the Earth's orbit, the perihelion and aphelion points are placed in early January and July. However, the time it takes for the Earth to move between these astronomical points, January to July is 72 hours less than the time it takes to move from July to January, sweeping out equal areas in unequal times. Thus, applying Kepler's Law to determine the perihelion and aphelion of the Earth's orbit disproves Kepler's Law!
If it doesn't work for Earth why would it work for any other planet?
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DPCrisp
In: Bedfordshire
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| You need a force to accelerate it then another force to retard it and then another force to accelerate it again on a constant basis every orbit. |
Er, no. One, central force is sufficient to explain an orbit. Speeding up and slowing down is just a matter of how the acceleration lines up with the velocity.
You don't say you need one effect to increase the pitch of an on-coming police siren, then another to leave it at natural pitch along side you and a third to drop the pitch as it speeds away. You don't need to break down the police car's motion into 3 sections either.
| With a primary moving dragging its satellite along with it while that satellite is orbiting at a constant rate the same effect is produce without the need for all that accelerating and braking. |
If the Sun weren't orbiting around the centre of the galaxy, what would our orbit around the Sun be like? Why would we be orbiting at all?
| How can you tell if you are not taking direct measurements from each individual planet. All aphelions and perihelions are determined mathematically with Kepler's Law. |
Are they. How? Not just the distances, I mean, but the orientations of the orbits. I don't know of a Keplerian or Newtonian Law that determines those. And they're not all lined up, as if dragged, in the Sun's wake.
| What current force pray-tell is keeping the Earth spinning on its axis. |
What makes you think it needs one? In the Newtonian view, there are forces acting on Earth all the time, some of which are reckoned to be retarding the rotation. Newtonian cosmology does have everything in motion all the time, with no perfect conics or straight lines.
Newtonianally, forces change energy. To the extent that the energy of the spinning Earth does not change, there are no forces to inquire about.
| I wouldn't mention your belief in a current force to any of your astrophysics friend -- they take a dim view of heretics. |
Perhaps I misunderstand what you mean by "current force". I suspect all astrophysicists are my enemy, but they all believe in forces acting at all times. I didn't get the bit where you made a special thing of the "current" forces exerted by the juggler, as if the force acting during the ballistic phase of the ball's trajectory was not continuous... or something.
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DPCrisp
In: Bedfordshire
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| Chad wrote: | | Komorikid wrote: | | In a way all planets are. It's only the Sun's slow movement that stretches the distance out causing them to sweep out a larger arc behind the sun than in front of it. |
Then the elliptical orbits of all the Solar planets should be aligned in the same direction... unfortunately they aren't. |
They don't have inceasing eccentricities either. And as for the comets...
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