Results

Edmond Halley had envisaged a method in which observers could agree on the timing of a transit to the precise second.
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The most crucial moment was “internal contact”, when Venus should have been a perfect circle touching the edge of the Sun. Instead, it often appeared elongated and distorted. How could a precise instant of contact be established when Venus was afflicted with this problem of the “black drop”?
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Even if an expedition’s observers could reconcile their own results, there was the further problem of comparing them with others from around the world.
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Working with a mass of data required not just mathematical proficiency and stamina, but the ability to select. Precision astronomy here depended ultimately on individual judgement.