Academic Reading — Test 14

Reading passage

For thousands of years, people have looked upwards and attempted to record the positions of the stars. Early astronomers worked with little more than the naked eye, and even after the invention of the telescope, measuring exactly where a star sat in the sky remained extraordinarily difficult. The branch of astronomy devoted to such measurement is called astrometry, and it has always faced a stubborn obstacle: the stars are so remote that their apparent movements are minuscule. To chart the heavens with genuine precision, astronomers needed an instrument that could observe from beyond the blurring influence of the Earth's atmosphere. This ambition was finally realised by the European Space Agency through a spacecraft named Gaia, which was launched in December 2013. Gaia was not placed in orbit around the Earth. Instead, it was sent to a location roughly one and a half million kilometres away, on the side of the planet facing away from the Sun. This region, known as the second Lagrange point, offers a remarkably stable thermal and gravitational environment, which is essential when one is trying to measure angles smaller than the width of a human hair seen from many kilometres away. From this vantage point, the spacecraft slowly rotated, sweeping its two telescopes across the entire sky again and again over a period of years. Because each star was observed many times from slightly different positions as Gaia travelled with the Earth around the Sun, its distance could be calculated using a method known as parallax, the tiny apparent shift of a nearby object against a more distant background. The heart of the spacecraft was an enormous digital camera, the largest ever flown in space, containing nearly a billion pixels. This camera did not produce conventional photographs. Rather, it registered the precise moment at which the light of each star crossed its sensors, allowing the position of that star to be fixed with astonishing accuracy. Gaia could measure stellar positions to a precision that, by some comparisons, would be equivalent to detecting the diameter of a coin placed on the surface of the Moon. Over the course of its mission, it recorded not only where stars were located but also how they were moving, building up a dynamic picture rather than a static one. The volume of information gathered was staggering. Gaia observed close to two billion stars, although its core catalogue of high-precision measurements covered roughly one billion of them, a figure that nevertheless represents only about one per cent of all the stars thought to exist in our galaxy. The raw data streamed back to Earth had to be processed by a large international consortium of scientists, who developed sophisticated software to convert billions of individual observations into a coherent three-dimensional map. The first substantial release of this data appeared in 2016, and subsequent releases progressively refined and expanded the catalogue. Importantly, all of the resulting information was made freely available to researchers and the public alike, ensuring that the mission's benefits were widely shared. The scientific consequences of this map have been profound. Astronomers have used Gaia's measurements to trace the structure of the Milky Way, revealing that our galaxy bears the scars of ancient collisions with smaller neighbours. The data have helped to clarify the distances to stars that serve as cosmic measuring rods, thereby improving estimates of the size and age of the wider universe. Beyond the stars themselves, Gaia has detected thousands of asteroids within our own Solar System and has contributed to the discovery of planets orbiting distant suns. Because the spacecraft measured motion as well as position, researchers can even run the map forwards or backwards in time, modelling how the night sky will gradually change over hundreds of thousands of years. Gaia's working life eventually came to an end when its supply of cold gas, used to control its orientation, was exhausted. Yet the mission's true legacy lies not in the spacecraft but in the catalogue it produced. That archive will be studied for decades to come, and many of its most important discoveries are likely to be made long after the instrument itself fell silent. In transforming a centuries-old quest into a precise digital atlas, Gaia did not merely add to human knowledge of the stars; it redrew the map of the galaxy we inhabit.