Specifically , those tables used for most of the 20th century were Newcomb 's Tables of the Sun ( used from 1900 through 1983 ) and Brown 's Tables of the Moon ( used from 1923 through 1983 ) .
Because this second was the independent variable of time used in ephemerides of the Sun and Moon during most of the twentieth century ( Newcomb 's Tables of the Sun were used from 1900 through 1983 , and Brown 's Tables of the Moon were used from 1920 through 1983 ) , it was called the ephemeris second .