Transit drawings capture contact uncertainties

Teams at widely separated sites recorded the transit to help estimate the Earth–Sun distance.

Astronomers sought to compare the instants when Venus crossed the solar limb across different locations.

The indistinct contact of Venus with the solar edge complicated the measurements made at this transit.

Cook and Green recorded the transit from Tahiti during an international observing campaign.

European expedition members observed from an island with its own navigational and celestial knowledge traditions.

Observations from Tahiti were compared with observations elsewhere to estimate the scale of the solar system.

He recorded a small object in Gemini, at first thinking it might be a comet.

Later observations showed that Herschel's object was a planet beyond Saturn.

The first modern discovery of a planet began with this observation.

The precise dated sighting enabled other astronomers to establish the object's orbit.