Burnham's micrometer, 19th century. This device was designed and built by US astronomer Sherburne Wesley Burnham (1838-1921). Micrometers, when used in astronomy, are precision measuring instruments used to help measure the position of stars and other objects observed through a telescope or recorded on a photographic record of a telescope observation. Burnham mostly observed double stars, publishing the Burnham Double Star Catalogue in 1906 after 36 years of work. The catalogue contained his recordings of the positions of 13,665 double stars. This is the filar micrometer he devised in around 1880.
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