Speed of Gravity?

TVF, I have been reading your papers as well as details from JPL about the location of the solar center. You say the sun is 20s(of arc) from where it seems to be due to the 8 minutes it takes light to get from the sun to Earth. JPL will not comment on this matter and say the barycenter is the center. That point is a lot more than 20s from where the sun seems to be. So, my question is: How do you know the location of the center is 20s from the apparent location? Where is the data that proves this? And, by the way, JPL is only working with a model that works not real forces so lets do a pass on that part of the issue and focus on the data indicating a 20s location.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />How do you know the location of the center is 20s from the apparent location? Where is the data that proves this?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The data consists of the daily transit circle observations of the Sun made at places such as the U.S. Naval Observatory. Those observations prove that the Sun's apparent direction is 20" (" is the symbol for arc seconds) west of the geometric center of its circular path around the Earth. (Technically, the "center" is really the focus of an ellipse. But let's not introduce unneeded complications.)

The fact that the apparent Sun differs from the true Sun by 20 arc seconds is not disputed by anyone. Why would it be? The Sun is 93 million miles away, so its light takes 8.3 minutes to get here. During that 8.3 minutes, the Sun moves 20" relative to the star background. So it is evident that, if the light arrived instantly instead of after a delay, we would see the Sun 20" farther along in its cycle.

The barycenter is a completely different issue because it is an unobservable, completely-theory-determined, arbitrary point. It is not involved in the "speed of gravity" issue.

The observations proving that the Sun's gravity acts from the center of its circular path through the stars, and not from the delayed position of the Sun, are radar ranging observations. But that fact was never in doubt because Newton's law of gravity would have failed long ago if that were not true. -|Tom|-

So, it is a fact the center of the orbit of Earth is observed to be 20" from the apparent position. The JPL generator has the center at a position way different than that. How is it able to generate accurate tables if it is that far off the mark? I am not questioning either position but maybe I'm getting something wrong since they seem to be locating the solar system center in different places.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />The JPL generator has the center at a position way different than that. How is it able to generate accurate tables if it is that far off the mark?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The choice of "center" for computing orbits for the whole solar system can be anywhere, even at Alpha Centauri. Because there is no mass at the center, it does not affect the calculation of orbits.

The barycenter is an arbitrary, fictitious, unobservable point. Both the Sun's true and its apparent positions as seen from Earth are specific, real, and observable. -|Tom|-

The center of choice at JPL/horizons is the point the Earth orbits according to the generator. That point is not anywhere near the point you say is the center of gravity and where the orbit of Earth is centered. Does the Earth's orbit two centers? That is unlikely if not impossible. Is the orbit of Earth observed to be centered where you say it is or at the barycenter that JPL has is at? I suppose the two centers may have different meanings than center of the orbit. It is very confusing to me how two different locations are centers of the same orbit.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />It is very confusing to me how two different locations are centers of the same orbit.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The barycenter is an origin for measuring coordinates, but *not* a center for any orbit. Think of a satellite orbiting the Earth. The center of its orbit is Earth's center. But I might measure the height of the satellite from, say, Cleveland. Then Cleveland is my origin for measurements.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">The center of choice at JPL/horizons is the point the Earth orbits according to the generator.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">No, it is an origin for coordinates, not a center. There is a difference.

Let me give another example. Suppose we discover that nearby star Alpha Centauri (AC) is actually orbiting our Sun. (It isn't, but it could be,) If we decide to include AC in our calculations, the barycenter suddenly shifts half way to AC. Discovering "Planet X" might shift it a more modest amount, but that could easily be outside Earth's orbit. Obviously, Earth could not be orbiting a point outside its own orbit.

Likewise, Earth is not orbiting JPL's barycenter. That is merely an origin for measurement, but not a center. -|Tom|-