Page "William Herschel" Paragraph 9

Herschel's early observational work soon focused on the search for pairs of stars that were very close together visually.

Astronomers of the era expected that changes over time in the apparent separation and relative location of these stars would provide evidence for both the proper motion of stars and, by means of parallax shifts in their separation, for the distance of stars from the Earth ( a method first suggested by Galileo Galilei ).

From the back garden of his house in New King Street, Bath, and using a, ( f / 13 ) Newtonian telescope " with a most capital speculum " of his own manufacture, in October 1779, Herschel began a systematic search for such stars among " every star in the Heavens ", with new discoveries listed through 1792.

He soon discovered many more binary and multiple stars than expected, and compiled them with careful measurements of their relative positions in two catalogues presented to the Royal Society in London in 1782 ( 269 double or multiple systems ) and 1784 ( 434 systems ).

A third catalogue of discoveries made after 1783 was published in 1821 ( 145 systems ).