AWhat changed
Shapiro and colleagues tested the extra round-trip delay of radar signals passing near the Sun using planetary echoes. Their 1968 preliminary analysis combined orbital modeling with Mercury and Venus observations and reported agreement with the general-relativistic delay within the estimated experimental uncertainty. A later 1971 analysis combined further Haystack and Arecibo measurements and fitted a delay scale of about 1.02 relative to the general-relativistic prediction of 1, with an estimated 0.05 uncertainty including systematics.
Scientific scope
Shapiro and colleagues tested the extra round-trip delay of radar signals passing near the Sun using planetary echoes. Their 1968 preliminary analysis combined orbital modeling with Mercury and Venus observations and reported agreement with the general-relativistic delay within the estimated experimental uncertainty. A later 1971 analysis combined further Haystack and Arecibo measurements and fitted a delay scale of about 1.02 relative to the general-relativistic prediction of 1, with an estimated 0.05 uncertainty including systematics. The measurements use joint orbital and timing models, rather than directly observing a coordinate-time quantity independent of model assumptions. In 1968 the authors report a hardware-processing defect requiring empirical correction and unresolved inter-observatory differences; they state raw measurements were not retained for complete reprocessing. The 1971 systematic estimate includes solar plasma and planetary topography. The 1968 report gives a delay coefficient of 0.9 ± 0.2, whereas the 1971 text cites 0.09 ± 0.2 for the earlier result; this conflicts with the earlier paper and adjacent conversion, and the effect of the 1968 erratum remains unresolved. These reports share observations and have distinct bylines; they are separate from the 1964 theoretical proposal and later spacecraft tests.
Evidence
The linked original works support the scoped statement and contribution attribution. WRS has not independently replayed experiments or reconstructed a full mathematical proof. The measurements use joint orbital and timing models, rather than directly observing a coordinate-time quantity independent of model assumptions. In 1968 the authors report a hardware-processing defect requiring empirical correction and unresolved inter-observatory differences; they state raw measurements were not retained for complete reprocessing. The 1971 systematic estimate includes solar plasma and planetary topography. The 1968 report gives a delay coefficient of 0.9 ± 0.2, whereas the 1971 text cites 0.09 ± 0.2 for the earlier result; this conflicts with the earlier paper and adjacent conversion, and the effect of the 1968 erratum remains unresolved. These reports share observations and have distinct bylines; they are separate from the 1964 theoretical proposal and later spacecraft tests.
Contributors
- The named authors in the research record · SCIENCE: These are the listed authors of the cited contribution sources. Paper authorship does not quantify individual effort. An incomplete list is explicitly marked; same names are not automatically merged.
- Fourth Test of General Relativity: New Radar Result
- Fourth Test of General Relativity: Preliminary Results
Provisional WRS assessment, edition 2026-10-28.1. Independent expert calibration is pending. This grade does not certify correctness or assign ownership.
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