Mercury's Perihelion Precession

Maybe the unit of time has to be defined since the Earth is precessing too. Is one year equal to 31,557,168 seconds? That seems to be the time of one 360 degree rotation of the Earth on average over several thousand years.

<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 />Maybe the unit of time has to be defined since the Earth is precessing too. Is one year equal to 31,557,168 seconds?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">No. It is 31,557,600 seconds for the Julian year. Let's see now. In 4000 years, that makes an error of 20 days. That could give an error of 2 degrees per century in Mercury's position, not counting a possible 1.4 degrees per century from precession -- all assuming you used Mercury itself instead of Mercury's perihelion to judge the change. Did you do that?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">That seems to be the time of one 360 degree rotation of the Earth on average over several thousand years.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Measured relative to what? Equinox? Perihelion? Node on invariable plane? Fixed stars? Or some calendrical system of human invention?

Jim, you don't know what you are doing. Kindly do not consider it rude if I ignore your future posts on this and related subjects. If you don't have my message by now, nothing more I can say will convey it. -|Tom|-

The attempt I am making to get a measurement can be improved on thats for sure. But, still the precession of Mercury's orbit is easy to see in the tables the generator produces. It is just a matter of extracting the correct measurement. I am using a year as the time it takes the Earth to orbit the sun one time and that time also is in the generator&gt; It is not an arbitrary calander unit.

Thomas, Reguarding your original question there seems to be more misinformation than real factual stuff about the precession of the perihelion of Mercury. This is very perplexing for me and if you learn anything new please post it. The JPL/horizons generator shows about a 70"/yr precession but the asy an astronomer says 6"/yr is the correct number. I haven't found anything about anyone actually checking if the precession story is true or not in the light of new and better data. The astronomical elite seem to rubber stamp prior results as TVF explains above so they are no help. It is an interseting project.

Thomas, It should also be said the rate of Mercury's perihelion is observed in a precessing system so that may be why two different numbers exist. The larger total includes the precession of the whole system precession and the smaller rate is for Mercury within the system. I guess that makes sense and seems simple enough.

<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 />Thomas, Reguarding your original question there seems to be more misinformation than real factual stuff about the precession of the perihelion of Mercury. This is very perplexing for me and if you learn anything new please post it. The JPL/horizons generator shows about a 70"/yr precession but the asy an astronomer says 6"/yr is the correct number. I haven't found anything about anyone actually checking if the precession story is true or not in the light of new and better data. The astronomical elite seem to rubber stamp prior results as TVF explains above so they are no help. It is an interseting project.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Jim,

I don't know the figures above. The ones I have are as follows:

The total apparent precession of Mercury's perihelion (as observed from the earth) is 5600"/100yr . Of this, 5025" is due to the earth's precession (precession of equinoxes) and 532" due to planetary perturbations of Mercury's orbit. This leaves 43"/100yr unexplained.

The history of the discovery of this discrepancy is actually quite dubious:
in 1859 Leverrier analyzed records of 16 Mercury transits of the sun (dating from 1677 to 1848) and found a discrepancy of 38"/100yr. However, he was not able to fit this through a perihelion advance alone but concluded that there must also be a change in the eccentricity of Mercury's orbit. He could not determine the latter accurately but after additionally analyzing 400 meridian transits of Mercur concluded that it contributed negatively and adopted a value of -22" i.e. the perihelion precession became 38"+22"= 60"/100yr (from specific meridian observations he got even a value of 131"/100yr). Then suddenly, when he prepared his tables, he arbitrarily decided to set the eccentricity change to 0 and thus ended up with the 38" for the perihelion advance.
In 1882-1895 Newcomb then suggested several values between 42"-43" for the perihelion advance again arbitrarily neglecting any change of eccentricity of the orbit.
In 1916 Einstein gave his own interpretation of the effect in terms of GR and it is his theoretical value and not observational data that has been used ever since to calculate the ephemerides .

References.:
N.T. Roseveare: Mercury's Perihelion from Leverrier to Einstein
G.A. Cherbotarev: Analytical and Numerical Methods of Celestial Mechanics

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