[quote source="/post/105664/thread"
From WUWT
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Leif Svalgaard
September 7, 2013 at 9:08 pm
David Thomson says:
September 7, 2013 at 5:55 pmLook at the Earth – Moon system. The center of gravity of these two bodies is neither in the Earth nor the Moon, yet both orbit the barycenter. The Sun does the same thing.
Great confusion here. The Earth+Moon orbits the center of the Sun as do all other planet+moon systems. You do not need to understand the theory [although it is simple enough]. We have very precise measurements of the Earth’s orbit and they show that the E+M orbit the center of the Sun. A simple consequence hereof is the measured value of TSI which varies with the square of the distance to the center.
"My bold.
Leif is correct. At this very moment in time the Earth is orbiting the center of the Sun, while simultaneously the Sun is experiencing the gravitational pull of Earth. Although at each moment of time the Earth can only be orbiting the center of the Sun, when the historical orbital path is viewed, the Sun is seen to be orbiting the center of mass of the Sun and Earth.
So the Sun
is wobbling because of the Earth, and yet the Earth can only be orbiting the center of the sun at each moment of time.
Leif knows the Sun orbits the SSBC
Leif Svalgaard
June 29, 2008 at 1:21 pm
There are two issues here:
1) barycentric motion
2) planetary tides
The standard [and correct I think] objection to the barycentric motion having any effect is that the Sun is in free fall around the barycenter and therefore does not feel any forces from that [Equivalence postulate of General Relativity or some such, or in simpler terms: the gravitational and centrifugal forces balance completely].
The standard [and correct I think] objection to the planetary tides is that they are too small.
To illustrate how confusing the subject can become here are two different conversations from WUWT involving Leif
Conversation 1. --------------------------------------------------------------------------------------------------
papertiger
August 1, 2008 at 9:33 pm
Speaking of wobbles, Jennifer Marohasy contributor, Dr. Ian Wilson of the University of Southern Queensland, has written up a study of the Sun’s orbit around the solar system’s center of gravity, and makes a case for it being in direct control of Pacific Decadal Oscillation. (PDF here)
Should we be compensating the flux value for that wiggle also?
Leif Svalgaard
August 2, 2008 at 7:05 am
papertiger: the Sun’s orbit around the solar system’s center of gravity, and makes a case for it being in direct control of Pacific Decadal Oscillation.
Should we be compensating the flux value for that wiggle also?
No, as the wiggle is purely fictive. It is not the Sun that moves, but the center of gravity that moves as the planets move around. So the distance between the Sun and the Earth stays what it is no matter where the other planets are [to very high precision – there are very, very tiny gravitational perturbations]. The easiest way to observationally [because I have found that many people cannot or won’t understand the theory] verify that is simply to measure the distance. The relative changes in TSI can be measured with amazing precision [0.007 W/m2 against a TSI value of 1361 W/m2 – that is 1 in 200,000], and measurements of TSI by SORCE shows that the observed values of TSI vary just as they should as if the distance between the Sun and the Earth stays what it is no matter where the other planets are. Here is a plot of the observed variation of TSI [black line] and what TSI should have been according to the barycenter people [e.g. here]. And here is their Figure 10 showing some predicted values of TSI if the Sun wiggled around. The red dots on the previous Figure show their predicted values. They do not match at all. Carsten Arnholm, Norway
August 2, 2008 at 11:37 am
Leif Svalgaard:
“
No, as the wiggle is purely fictive. It is not the Sun that moves, but the center of gravity that moves as the planets move around.”
Can you clarify this please.
I think this is wrong,......
The sun clearly wiggles….Leif Svalgaard
August 2, 2008 at 2:36 pm
Carsten Arnholm:
When one says that something moves one must also say in relation to what. As the question was if the radio flux would have to be adjusted because of the Sun’s ‘movement’, the reference point was clearly the Earth. I gave an observational test that shows that the Earth also moves such that the distance between the Sun and the Earth is that corresponding to no other planets present [the Sun and the Earth moving around ‘their’ center of mass – to high precision, if we take the barycenter to be the arbitrary reference point], hence no ‘jerking around’ of the Sun by the other planets. Did you take the trouble to go check the Figures? Or the SORCE TSI? So, just as TSI is observed not to be influenced by the wiggle, so is the f10.7 flux also not affected, as that was the answer I gave. It is utterly amazing that people still don’t get this. Conversation 2. ----------------------------------------------------------------------------------------
John-X
August 3, 2008 at 4:38 pm
Leif Svalgaard:
You need to edit the Wikipedia page on “Center of Mass”
en.wikipedia.org/wiki/Center_of_mass#Barycenter_in_astronomyto clear up the misstatements there, such as,
“The Sun orbits a barycenter just above its surface” due to the mass of Jupiter.
The animations on the page are very misleading, as they clearly show objects “in freefall” orbiting around a common barycenter.
So if you can edit this Wikipedia page, you can probably help prevent some misunderstandings.
But I don’t suppose you can do anything about this guy and his “Gravity Simulator” program, which clearly shows the discredited “Barycenter” idea, with the sun moving all around systematically in that crazy “trefoil” pattern.
orbitsimulator.com/gravity/articles/ssbarycenter.html Leif Svalgaard
August 3, 2008 at 9:04 pm
John-X: I have no desire to rewrite the Wikipedia entry. It is OK as it is. What is wrong is how people interpret what they read. Let us go through some simplified exercises.
Imagine a solar system with a Sun and a Jupiter in a perfectly circular orbit [same masses and almost same distance as our real solar system such that the Jupiter revolution takes 12 years] and for the time being, no other bodies. This is actually a fair approximation to our real system because Jupiter’s mass is greater than all the other planets together.
In this system, the center of mass [CM] will be on the Sun-Jupiter line always at the same distance [1,000,000 km or so – I didn’t calculate it precisely, because it doesn’t matter much] from the center of the Sun, a bit outside of the Sun. Seen from the Sun, Jupiter will complete one full revolution every 12 years and the CM will also, because it is on the Sun-Jupiter line, always right in front of Jupiter. So, the CM orbits the Sun, as seen from the Sun.
Seen from Jupiter, the Sun completes one full revolution in 12 years, and the CM also, as it is on the Jupiter-Sun line, right in front of the Sun, just a tad closer to Jupiter than the solar surface. Neither the Sun nor Jupiter will feel any forces because the gravitational force is precisely balanced by the centrifugal force of the orbital movement
. At all times, the distance between the Sun and Jupiter would be the same.
Seen from the CM [it is actually impossible to put a free observer there, not because the Sun is too hot, but because at the distance of only a million km from the center of the Sun, the orbital period would be very short rather than 12 years – but let that slide, this is a thought experiment after all, and as I have said in earlier posts, it is allowed to not follow the laws of Nature]
The Sun would be observed by that observer to revolve about the CM in precisely 12 years and Jupiter would too, located at the opposite point in the sky. Because an observer on the Sun already does not feel any forces [we are ignoring the already calculated minute tidal forces that raise the surface by a hard to measure one thousandth of a meter], us placing an imagined observer at the CM seeing the Sun compete a very tight orbit about the CM would not suddenly cause the observer on the Sun to feel anything.
I could now add another planet [or my little pea from a previous discussion] to displace the CM somewhat. That would still not affect the motion of Jupiter and the Sun [except from very, very small gravitational perturbations], nor, all the sudden cause the observer on the Sun to begin to feel any forces. The CM would now not move in the neat circles from before, but in a more complicated path because of the new planet. Seen from the Sun, the two planets would still move in their perfectly circular orbits with their distances being constant. But, as the CM now moves in a complicated path, the Sun [and the planets] will seen from the gyrating CM move in correspondingly complicated orbit{s}. But this is only because we have chosen to view the Sun from a wildly moving point, just like the trees on a downhill mountain side seem to weave left and right seen by a slalom skier completing her run.
This is about as clear as I can make it. If this does not work, I don’t know what else to say.
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