I can aim a rifle, iron sights, within one arc minute. With pistol it is about 3 arc minutes. Astronomers using iron sights can do as well on stars. With precision gears and some optical aid they can measure much finer. Still, 50 to 100 parsecs is considered adequately far for that technique with telescopic magnification, and one parsec, as for Alpha Cent, is iron sights accuracy. For greater distance they like to use absolute magnitude.
You can shoot pretty good as can I, but we are dealing in a couple of hundred yards. When you can hit a pop can at 25 miles with iron sites give me a jingle.