Orbital speed of Earth

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by makis</i>
<br />Is this a wish or something that referes to actual, undisputable data?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The latter.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">IMO based solely on measurements and observations, this is not possible.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">You are curiously silent about what "measurements and observations" lead you to such a strange conclusion. 300 years of "measurements and observations" by astronomers worldwide say otherwise.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Do you know where I can get that Earth velocity graph relative to the Sun that is based solely on observations?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">JPL and USNO publish high-precision ephemerides of all major solar system bodies based on all available data. If you want the raw data, go to NSSDC. For the results, look up the JPL Development Ephemeris series, or one of the many USNO publications such as the <i>Astronomical Almanac</i>. It has a nice companion volume, the <i>Explanatory Supplement to the Astronomical Almanac</i> (P.K. Seidelmann, ed., University Science Books, 1992). But you might find the 1961 edition of this companion volume far more readable for non-professionals because there were fewer observation types back then, and you are obviously not interested in velocities to an accuracy of parts per billion.

Of course, ephemerides such as these give 3-D positions as a function of time. But as you say, "Differentiation of position data gives velocities. I have done enough experimental work with interferometers to know that." So you should have no trouble getting an Earth velocity graph from the Earth-Sun position data.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">I thought astrologers use the geocentric system, something very similar if not identical to the Ptolemaic system, where the motions of planets are epicycles resulting in retrogate motion.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">That is another misimpression. Read the "Explanatory Supplement" and you will understand astronomical coordinate systems much better. Both geocentric and heliocentric systems are in current use, depending on the application. For example, if tracking artificial satellites, we would use a geocentric system. But we also use it for the whole solar system when preparing tables of where the various bodies will be seen by Earth-based telescopes. The paths of the planets relative to the stars, as viewed from Earth, really are "epicycles", which is why the Ptolemaic system survived longer than the heliocentric system has even existed.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">So what is the 'actual', 3-dimensional motion of the Earth around the Sun? If it's not an ellipse, what does it look like? Any references or links to graphs?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The orbit of the Earth is a perfect ellipse to the accuracy that the human eye can perceive. It is only modern, high-precision data that can see deviations from a perfect ellipse, caused primarily by perturbations induced by gravitational forces from other planets. -|Tom|-

The data is way too hard to access but I have hope it will become an easy matter when enough people get involved. Anyway, the moon speeds and slows the Earth by 12m/s according to the post above. I assume the Earth is slowed most at 1st quarter and speeded up 24m/s by the 3rd quarter. Then slows down 24m/s getting back to 1st quarter. Please correct if I have it wrong, thanks.

<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 />I assume the Earth is slowed most at 1st quarter and speeded up 24m/s by the 3rd quarter. Then slows down 24m/s getting back to 1st quarter.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">You have it right. Looking at the in-plane longitudinal effect only, Earth's average orbital speed is about 30,000 m/s, increasing by about 500 m/s in January and decreasing by 500 m/s in July because the orbit is an ellipse, not a circle. Overlaid on that is the +/- 12 m/s effect from the Moon, just as you described. The next largest effect, about +/- 1 m/s, is due to Jupiter. -|Tom|-

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by tvanflandern</i>
The orbit of the Earth is a perfect ellipse to the accuracy that the human eye can perceive. It is only modern, high-precision data that can see deviations from a perfect ellipse, caused primarily by perturbations induced by gravitational forces from other planets. -|Tom|-
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Thank a lot Dr. Van Flander. All these plus more tends to support the hypothesis that there must exist a carrier of gravitational energy to affect deviations from purely inertial paths, such as circles and ellipses. In this respect I think GR is problematic unless one assumes that the 4-D space-time acts as a medium of gravitational energy propagation, since the metric is just a mathematical description of the variable curved properties of space-time and cannot serve that purpose.

I think this is highly troublesome for a theory such as GR. Although I have been questioning strongly your unobservable graviton particle theory, I come to realize that an energy/momentum transfer mechanism between real bodies in gravitational orbits is mandatory to avoid considering other hypotheses such as for instance that our physical reality is a computer simulation.

Still, I'm very skeptical about the graviton hypothesis as a momentum transfer agent and essentially the cause of gravitation but I recommened to people I have discussions with to take an unbiased look at your theory.

One thing is for sure, the observable orbits of cellestial bodies entail much more background activity than what GR assumes to take place and such activity is physical and real. More important is where that activity takes place which is not accounted for in the foundations of GR.

Makis

Hoping to keep this a simple a possible I'll focus on the Earth/moon motion and skip whatever effect Jupiter and Venus generate. The force of the moon causes the Earth to speedup and slow down is calculated from F=ma and amounts to ~24m/s as posted above. The acceleration rate changes from zero at new and full moon to the maximiun rate at 3rd and first quarter. My question: What is the effect of this force on Earth? Or how is this force observed(data) to manifest itself? In the barycenter model shown at JPL/horizons web site this force is applied in reverse and that causes the moon to be nearer to the sun at full moon and farther from the sun at new moon.

<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 />What is the effect of this force on Earth?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">It changes the Earth's velocity, as already described.

In general, the only effect of gravity on a rigid body is to change the speed of the body. For a slightly non-rigid nody such as Earth, the fact that the Moon's pull is stronger on the nearside than on the farside causes Earth to bulge slightly toward the Moon. This is the simplest kind of "tide", a bulge toward the source of gravity. There is also a solar tide, a small bulge toward the Sun.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">In the barycenter model shown at JPL/horizons web site this force is applied in reverse and that causes the moon to be nearer to the sun at full moon and farther from the sun at new moon.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The Moon's distance from the Sun is dominated by the ellipticity of Earth's orbit. The ellipticity can change the Moon's distance from the Sun by +/- 2.5 million km over the course of a year. The diameter of the Moon's orbit is about 800,000 km.

However, because the distance change from ellipticity cannot exceed about 600,000 km in just the two weeks between Full and New Moon, the condition you described is not physically possible for any consecutive Full and New Moons. You misunderstood something. -|Tom|-