 The first direct measurement of the distance to a star ( 61 <unk> at 11 @.@ 4 light @-@ years ) was made in 1838 by Friedrich <unk> using the parallax technique . <unk> measurements demonstrated the vast separation of the stars in the heavens . Observation of double stars gained increasing importance during the 19th century . In 1834 , Friedrich <unk> observed changes in the proper motion of the star Sirius and inferred a hidden companion . Edward Pickering discovered the first spectroscopic binary in 1899 when he observed the periodic splitting of the spectral lines of the star <unk> in a 104 @-@ day period . Detailed observations of many binary star systems were collected by astronomers such as William <unk> and S. W. <unk> , allowing the masses of stars to be determined from computation of orbital elements . The first solution to the problem of deriving an orbit of binary stars from telescope observations was made by Felix <unk> in 1827 . The twentieth century saw increasingly rapid advances in the scientific study of stars . The photograph became a valuable astronomical tool . Karl <unk> discovered that the color of a star and , hence , its temperature , could be determined by comparing the visual magnitude against the photographic magnitude . The development of the <unk> <unk> allowed precise measurements of magnitude at multiple wavelength intervals . In 1921 Albert A. <unk> made the first measurements of a stellar diameter using an <unk> on the <unk> telescope at Mount Wilson Observatory . 
