In 1838 , astronomer Friedrich Wilhelm Bessel measured the parallax of the star 61 Cygni successfully .
In 1838 , astronomer Friedrich Wilhelm Bessel disproved Ptolemy 's claim that parallax motion did not exist .
In 1838 , astronomer Friedrich Wilhelm Bessel measured the parallax of the star 61 Cygni successfully , and disproved Ptolemy 's claim that parallax motion did not exist .