HD 140283 is an extremely metal-deficient and high-velocity subgiant in the solar neighborhood , having a location in the HR diagram where absolute magnitude is most sensitive to stellar age .
Because it is bright , nearby , unreddened , and has a well-determined chemical composition , this star avoids most of the issues involved in age determinations for globular clusters .
Using the Fine Guidance Sensors on the Hubble Space Telescope , we have measured a trigonometric parallax of 17.15 \pm 0.14 mas for HD 140283 , with an error one-fifth of that determined by the Hipparcos mission .
Employing modern theoretical isochrones , which include effects of helium diffusion , revised nuclear reaction rates , and enhanced oxygen abundance , we use the precise distance to infer an age of 14.46 \pm 0.31 Gyr .
The quoted error includes only the uncertainty in the parallax , and is for adopted surface oxygen and iron abundances of [ O / H ] = -1.67 and [ Fe / H ] = -2.40 .
Uncertainties in the stellar parameters and chemical composition , especially the oxygen content , now contribute more to the error budget for the age of HD 140283 than does its distance , increasing the total uncertainty to about \pm 0.8 Gyr .
Within the errors , the age of HD 140283 does not conflict with the age of the Universe , 13.77 \pm 0.06 Gyr , based on the microwave background and Hubble constant , but it must have formed soon after the big bang .