雅思阅读机经—Transit of venus_雅思英语阅读

雅思阅读机经—Transit of venus

　　In the 18th century science continued to flourish. There were discoveries about the nature of gas, about electricity and about chemical reactions. The Swedish scientist Carolus Linnaeus developed schemes for classifying plants and animals based on the concept of individual species in relational hierarchies. Within this growing framework of science, some of the first great questions were addressed. How large is the solar system? How distant is the Sun from the Earth?

　　Most of us probably heard the phrase transit of Venus or transit of Mercury during primary school, in connection with Captain Cooks observation of the transit of Mercury at Mercury Bay, on the Coromandel Peninsula. It is a phrase of some significance in the development of science. But what does it mean? When Venus or Mercury passes directly between Earth and the Sun, the planet can be seen as a small black circle against the large brilliant orb of the Sun. Such events are known as transits. In 1663, James Gregory suggested that observation of a transit from widely spaced locations on Earth could yield an accurate estimate of the distance between the Earth and the Sun.

　　Jeremiah Horrocks, a young Englishman with a passion for astronomy, was the first person to accurately calculate the time of a transit and then observe it. From 3:15 P.M. on November 24, 1639, the 20-year-old watched a small black spot creep across the lower left side of the sun. A telescope in his darkened room projected the image onto a card. Using trigonometry and such other limited information as was available, he estimated the size of Venus and the solar distance. While his estimate was only about half the actual distance of the Earth to the Sun, it was better by a factor of ten than anyone elses up to that time. Horrocks died at the age of 22, almost unknown, but his observations gradually seeped out into the astronomical community.