 Transit observations in 1874 and 1882 allowed this value to be refined further . Three expeditions — from Germany , the United Kingdom and the United States — were sent to the Kerguelen Archipelago for the 1874 observations . The American astronomer Simon Newcomb combined the data from the last four transits , and he arrived at a value of about 149 @.@ 59 million kilometers ( ± 0 @.@ 31 million kilometers ) . Modern techniques , such as the use of radio telemetry from space probes , and of radar measurements of the distances to planets and asteroids in the Solar System , have allowed a reasonably accurate value for the astronomical unit ( AU ) to be calculated to a precision of about ± 30 meters . As a result , the need for parallax calculations has been superseded . 
 Transit observations in 1874 and 1882 allowed this value to be refined further . Three expeditions — from Germany , the United Kingdom and the United States — <a href='uninflect' title='1'><mark>were</mark></a> sent to the Kerguelen Archipelago for the 1874 observations . The American astronomer Simon Newcomb combined the data from the last four transits , and he arrived at a value of about 149 @.@ 59 million kilometers ( ± 0 @.@ 31 million kilometers ) . Modern techniques , such as the use of radio telemetry from space probes , and of radar measurements of the distances to planets and asteroids in the Solar System , <a href='been_done' title='2'><mark>have</mark></a> allowed a reasonably accurate value for the astronomical unit ( AU ) to be calculated to a precision of about ± 30 meters . As a result , the need for parallax calculations <a href='been_done' title='3'><mark>has</mark></a> been superseded . 
Transit observations in 1874 and 1882 allowed dis value to be refined further . Three expeditions — from Germany , the United Kingdom and da United States — was sent to the Kerguelen Archipelago for tda1874 observations . The American astronomer Simon Newcomb combined the data from the last four transits , and he arrived at a value of bout 149 @.@ 59 million kilometers ( ± 0 @.@ 31 million kilometers ) . Modern techniques , such as thdase of radio telemetry from space probes , and of radar measurements of thedastances to planets and asteroids in the Solar System , done allowed a reasonably accurate value fir the daronomical unit ( AU ) to b calculated to a precision of about ± 30 meters . As a result , the nda for parallax calculations done been superseded .