The difference in wavelength between the IR oxygen triplet 7772-7775 A in the sun and in the laboratory has been observed. Converted to velocities, the disk values, extrapolated to the limb, give a redshift of 655 m/s compared to the value of 636 m/s predicted from the principal of equivalence. Observations of the chromospheric oxygen lines in emission just off the sun's limb give a velocity of 627 m/s or 0.99 of the Einstein prediction.
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Lopresto et al. (1991) studied this question.