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:These error bars, and that of the general relativity prediction, all overlap.

:These error bars, and that of the general relativity prediction, all overlap.

There are at least 4 criteria that can be used for evaluating whether a manifestation of precession makes a good test:

Choosing a phenomenon to measure, and setting up an experiment to measure it, often benefits from a great deal of planning.  For example, the Lee-Yang-Wu experiment that disproved parity in the weak force, took months to plan, and only about 15 minutes to conduct.  Measurements of orbital precession due to general relativity are also aided by careful choice of the exact phenomena to measure.

The scientific community didn't have a lot of choice in how to measure the mechanical effects of general relativity in 1915.  The only manifestation that was known at the time was the precession of planetary orbits.  The orbit of Mercury was used because it has the highest precession of all the planets in the solar system.  This is because it moves faster than any other planet.  Though it is still nowhere near to being "relativistic", so the effect was extremely small.

#Is it free of "noise" confounding the observations?

The precession of Mercury satisfies #1, but it scores badly on #4, and totally fails #2 and #3.  The precession is actually quite small, and several decades of observation went into it.  Observing #2 and #3 are out of the question, though it has recently become possible to measure these for other phenomena involving black holes and neutron stars.

Also, Mercury does not score well on #4.  The calculated precession from relativity is 43 arcseconds per (Earth) century, in the context of 5600 arcseconds per century of total precession.  For most of the 20th century, the precession of Mercury, feeble and noisy as it was, was all anyone had to go on.  And there are questions about the various noise signals.  The vast bulk of the noise is the gravitational tugs from other planets (about 532 arcseconds), 0.03 arcseconds from solar oblatenes, 0.002 arcseconds from Lense-Thirring precession (a very subtle relativistic effect).

#The first question that is of interest is whether precession occurs, and how much.  The precession of Mercury had been known, with considerable accuracy due to observations of transits of the Sun, for about 50 years.  The precession does occur, and in very good agreement with theory.  The data on this are discussed just above in this article.

#We now have access to much better examples of orbits affected by general relativity, showing the effect much more strongly than could have been done in 1915.  This is because orbiting bodies emit [[gravitational waves]], which remove energy from the system and make the orbit decay.  This effect is utterly impossible to observe in the case of Mercury's orbit, but it became possible with the discovery of pulsars in 1967.  Binary pulsars are sufficiently massive, and orbit sufficiently closely, that their decay can be observed.  This was observed for binary pulsar [[PSR B1913+16]], and Joseph Taylor and Russell Hulse were awarded the 1993 Nobel Prize for this.  The gravitational waves themselves were still far to weak to be observed directly.

#In addition to the more recent discoveries involving much stronger "signals" than the observations of Mercury, those signals were much less contaminated by extraneous phenomena, or "noise".  The calculated relativistic precession of Mercury is 43 arcseconds per (Earth) century, in the context of 5600 arcseconds per century of total precession.  The latter effects are mostly due to the gravitational forces from other planets, 0.03 arcseconds from solar oblatenes, and 0.002 arcseconds from Lense-Thirring precession.

People have argued at great length (often here at Conservapedia) over the total precession discrepancy (about 1 arcsecond) and relativity's role in it, but in fact there are other phenomena that are vastly better suited to testing Einsteinian gravity.  These include black holes in galactic centers, quasars, neutron stars, and other black holes.

 

People have argued at great length (often here at Conservapedia) over the total precession discrepancy (about 1 arcsecond per century according to an article cited at Wikipedia) and relativity's role in it, but in fact there are other phenomena that are vastly better suited to testing Einsteinian gravity.

===The Shapiro Effect===

===The Shapiro Effect===