Maximilian Hell observing the transit of Venus, 1769.

Print of the Austrian astronomer Maximilian Hell (1720-1792) seated next to his astronomical quadrant, isued in 1771. The caption for this mezziotint, by J G Haid after W Pohl, indicates that Hell is observing the 1769 Transit of Venus from Lapland. These rare astronomical events that occurred in 1761 and 1769 allowed astronomers to accurately measure the size of the Solar System. Later after returning home, Hell was accused of fiddling his observation, a slur that was disproved until the ninetieth century.