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By comparison, the human eye can resolve structures separated by at best about 40 seconds of arc, and even the Hubble Space Telescope can achieve a resolution of only about 0.04 second of arc.

But measures of parallax made by Herman S. Davis and Wilsing seem to show a difference of parallax between the two components of about 0·08 of a second of arc.

Only a very few seconds apart they are or, in many cases, only the merest fraction of a second of arc.

By applying the interferometer method to Capella, arc distances of much less than one-twentieth of a second of arc were measured.

Its length is equal to the distance of a star whose parallax is one second of arc; that is, one parsec is equal to about three and a quarter light-years.