... reasonably precise measurements out to half a billion LY or so.
If anything, that's about two orders of magnitude too low; assuming only a factor of ten improvement in astrometric accuracy over what GAIA should achieve, you would nominally be able to measure parallax distances with a precision of ~ 10% or better out to about 20 billion parsecs (60 billion LY).
Of course, that's assuming a static, perfectly Euclidean universe; long before that point you have to take into account GR and cosmology, because the Euclidean approximations that are fine for parallax within our galaxy won't exactly hold any more...
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If anything, that's about two orders of magnitude too low; assuming only a factor of ten improvement in astrometric accuracy over what GAIA should achieve, you would nominally be able to measure parallax distances with a precision of ~ 10% or better out to about 20 billion parsecs (60 billion LY).
Of course, that's assuming a static, perfectly Euclidean universe; long before that point you have to take into account GR and cosmology, because the Euclidean approximations that are fine for parallax within our galaxy won't exactly hold any more...