Garth said:
This is nonsense: - "All space astrometry is relative to known star positions"
I could be wrong about that. Can you give me a counter example?
- so is the alignment of the GP-B gyroscopes 'relative to known star positions'.
I never said that.
GP-B does not measure the ecliptic longitude of the ecliptic.
I never said it does.
The gyroscopes are measured relative to the guide star. The guide star is being tracked by the VLBI and that tracking will detect the precession of the equinoxes if it measures the constantly updated RA and dec. of the star on the Earth based celestial sphere.
No. Precession is not observed by the VLBI. Precession is always computed using standard formulas.
The VLBI would measure the apparent place RA, Dec of IM Pegasi at each time of observation. To reduce an apparent place to a mean place at a standard epoch and equinox, I believe they must make the following corrections in order.
1. The effect of annual parallax.
2. The effect of annual aberration.
3. The effect of nutation.
4. The effect of precession.
5. The proper motion of the star.
The idea is that the mean place of any star at a standard epoch and equinox should be constant over time. The first four corrections are computed, not observed, and they are functions of time and place. The time argument is the difference between the observation time and the standard epoch time. The observed proper motion would be whatever it took to move the place after the fourth correction to the known mean place at the standard epoch and equinox.
In fact they are tracking the proper motion of the IM Pegasi relative to a distant quasar, so they will not detect this precession at all.
As I said, precession is not observed; it is computed. Quasars, like all stars, precess relative to the equinox.
Quasars have no parallax or proper motion, so steps 1 and 5 can be eliminated in the place reduction. So quasars provide a powerful check on the successive corrections for annual aberration, nutation, and precession. Now if you believe you know the effects of annual aberration and nutation to a very high precision, then you can use VLBI observations of quasars to "observe" general precession, and you can compare it to the results you got from the standard formula.
The precession of the equinoxes is well known and attributed to the lunar and solar differential gravitational forces on the Earth's oblate spheroid.
Yes, and that is a problem for the binary Sun theory. "Lunisolar" precession may consist of two components: the Newtonian-d'Alembert gravitational torques on the spinning tilted oblate Earth from gravitational forces from the Sun and the Moon plus the Sun's binary orbit motion. In the worst case, I think the Newtonian torques could be eliminated if the oblate Earth were hollow with a uniform shell thickness. If GP-B is observing a too-large "proper motion", I'm suggesting that it is due to the Sun's motion in a binary orbit.
There are nutations caused by the Sun's and Moon's changing relative positions.
Yes.
In addition to this lunisolar precession, the other planets, mainly Jupiter, cause the whole ecliptic to rotate, this planetary precession shift is only 0.47 seconds of arc per year (more than a hundred times smaller than lunisolar precession).
Yes.
All this is well modeled,
But is lunisolar precession modeled from first principles taking into consideration Earth's radial density profile, or is it modeled to match quasar observations? If the latter, then it can be questioned.
a binary solar companion would cause an further precession, which would be less than even this.
Smaller than 0.47 arcsec/year? Not hardly. If you assume the Sun is in a circular orbit a rate of 0.47 arcsec/year would correspond to an orbit period of 2.8 million years. We usually imagine much shorter periods and corresponding greater precession rates. But we don't need to speculate. GP-B can tell us how much it is. In fact, GP-B can refute the binary Sun hypothesis simply by not finding any excess "proper motion".
Such a precession has not been observed, although that was what I had thought you must been alluding to.
We are speculating that GP-B has observed it. If that turns out to be true, then I imagine other space telescopes can also observe it using their less precise gyroscopes.
The gravitational action of a hypothetical binary solar companion would not affect the GP-B gyroscopes any more than they would the alignment of other space telescopes. It will not affect their axial direction relative to the distant quasar, which is the ultimate reference point. Therefore the question of such a hypothetical binary solar companion has no place in this thread.
Garth
We are not talking about gravitational forces of the companion on the Earth inducing something akin to planetary precession. We are talking about the Sun following a curved path in space in its binary orbit. Such a curved path would produce apparent precession of the stars relative to the equinox. Imagine you are sitting on a merry-go-round across from the companion. If the merry-go-round rotated counter-clockwise, the objects on the horizon (analogous to stars) appear to the observer on the merry-go-round to rotate clockwise. Its just like what the stars do over the course of a year as a result of the Earth's orbit around the Sun.
-Glen
(And thank you Sylas!) predictions of the following alternative theories are as follows:
