Overview
This is a Gregorian reflector telescope – the type of telescope that Captain Cook and his astronomer, Charles Green, used. These telescopes were invented in 1661 by Scottish astronomer James Gregory. They had two specially shaped mirrors inside to focus the image.
While using these telescopes to observe the transit of Venus across the Sun, astronomers noticed that Venus had a fuzzy ring around it. This made it difficult for them to judge exactly when it began to pass the Sun, and many of their measurements were inaccurate.
The astronomers thought the fuzzy ring was Venus’s atmosphere. But it was actually caused by the sun heating up the mirrors in the telescopes!