剑桥雅思9Test2阅读Passage2原文翻译 venus in transit 金星凌日
剑桥雅思9 Test2 Passage1阅读原文翻译
June 2004 saw the first passage, known as a ‘transit’, of the planet Venus across the face of the Sun in 122 years. Transits have helped shape our view of the whole Universe, as Healther Cooper and Nigel Henbest explain
2004年6月，金星122年来首次穿过太阳面，称为“凌日”。正如Healther Cooper和Nigel Henbest 解释的那样，凌日帮助塑造我们对整个宇宙的看法.
On 8 June 2004, more than half the population of the world were treated to a rare astronomical event. For over six hours, the planet Venus steadily inched its way over the surface of the Sun. This ‘transit’ of Venus was the first since 6 December 1882. On that occasion, the American astronomer Professor Simon Newcomb led a party to South Africa to observe the event. They were based at a girl’s school, where—it is alleged—the combined forces of three schoolmistresses outperformed the professionals with the accuracy of their observations.
For centuries, transits of Venus have drawn explores and astronomers alike to the four corners of the globe. And you can put it all down to the extraordinary polymath Edmond Halley. In November 1677, Halley observed a transit of the innermost planet, Mercury, from the desolate island of St Helena in the south Pacific. He realized that, from different latitudes, the passage of the planet across the Sun’s disc would appear to differ. By timing the transit from two widely-separated locations, teams of astronomers could calculate the parallax angle—the apparent difference in position of an astronomical body due to a difference in the observer’s position. Calculating this angle would allow astronomers to measure what was then the ultimate goal: the distance of the Earth from the sun. This distance is known as the ‘astronomical’ or AU.
Halley was aware that the AU was one of the most fundamental of all astronomical measurements. Johannes Kepler, in the early 17th century, had shown that the distances of the planets from the Sun governed their orbital speeds, which were easily measurable. But no-one had found a way to calculate accurate distances to the planets from the earth. The goal was to measure the AU; then, knowing the orbital speeds of all the other planets round the Sun, the scale of the Solar System would fall into place. However, Halley realized that Mercury was so far away that its parallax angle would be very difficult to determine. As Venus was closer to the Earth, its parallax angle would be larger, and Halley worked out that by using Venus it would be possible to measure the Sun’s distance to 1 part in 500. But there was a problem: transits of Venus, unlike those of Mercury, are rare, occurring in pairs roughly eight years apart every hundred or so years. Nevertheless, he accurately predicted that Venus would cross the face of the Sun in both 1761 and 1769—though he didn’t survive to see either.
Inspired by Halley’s suggestion of a way to pin down the scale of the Solar System, teams of British and French astronomers set out on expeditions to places as diverse as India and Siberia. But things weren’t helped by Britain and France being at war. The person who deserves most sympathy is the French astronomer Guillaume Le Gentil. He was thwarted by the fact that the British were besieging his observation site at Pondicherry in India. Feeling on a French warship crossing the Indian Ocean, Le Gentil saw a wonderful transit—but the ship’s pitching and rolling ruled out any attempt at making accurate observations. Undaunted, he remained south of the equator, keeping himself busy by studying the islands of Mauritius and Madagascar before setting off to observe the next transit in the Philippines. Ironically after travelling nearly 50,000 kilometres, his view was clouded out at the last moment, a very dispiriting experience.
受哈雷关于确定太阳系规模的建议的启发，英国和法国的天文学家团队开始对各种地方（包括印度和西伯利亚）进行考察。但是，英国和法国的交战帮了倒忙。最值得同情的人是法国天文学家Guillaume Le Gentil 。英国人包围了他在印度Pondicherry的观察站，使他受挫。乘坐法国军舰穿越印度洋时，Le Gentil观测到了一次完美的凌日。但船的起伏和摇晃使得进行准确观测的尝试化为泡影。他没有因此而退缩，一直待在赤道以南，忙着研究毛里求斯和马达加斯加的岛屿，然后出发去菲律宾观测下一次凌日。具有讽刺意味的是，在行驶了将近50,000公里之后，他的视线在最后一刻被云层遮挡，这是非常令人沮丧的经历。
While the early transit timings were as precise as instruments would allow, the measurements were dogged by the ‘black drop’ effect. When Venus begins to cross the Sun’s disc, it looks smeared not circular—which makes it difficult to establish timings. This is due to diffraction of light. The second problem is that Venus exhibits a halo of light when it is seen just outside the Sun’s disc. While this showed astronomers that Venus was surrounded by a thick layer of gases refracting sunlight around it, both effects made it impossible to obtain accurate timings.
But astronomers laboured hard to analyse the results of these expeditions to observe Venus transits. John Franz Encke, Director of the Berlin Observatory, finally determined a value for the AU based on all these parallax measurements: 153,340,000km. Reasonably accurate for the time, that is quite close to today’s value of methods in accuracy. The AU is a cosmic measuring rod, and the basis of how we scale the Universe today. The parallax principle can be extended to measure the distances to the stars. If we look at a star in January—when Earth is at one point in its orbit—it will seem to be in a different position from where it appears six months later. Knowing the width of Earth’s orbit, the parallax shift lets astronomers calculate the distance.
但是天文学家们辛苦地分析了这些探险的结果，以观察金星凌日的现象。柏林天文台局长John Franz Encke 最终根据所有这些视差测量值确定了AU的数字：153,340,000 km。对于当时来说，这个数字已经足够准确，与当今雷达测量的数值（149,597,879km）十分接近。而雷达因其精准度已经取代了凌日观测和其他方法。AU是宇宙测量标杆，也是我们今天确定宇宙规模的基础。视差原理可以扩展到测量地球到恒星的距离。如果我们在一月份观测一颗恒星（当地球在其轨道上处于某一点时），其位置似乎与六个月后看到的位置不同。知道了地球轨道的宽度，视觉差可以让天文学家计算其距离。
June 2004’s transit of Venus was thus more of an astronomical spectacle than a scientifically important event. But such transits have paved the way for what might prove to be one of the most vital breakthroughs in the cosmos—detecting Earth-sized planets orbiting other stars.