According to a recent report on the website of New Scientist magazine in the UK, the International Liquid Mirror Telescope (ILMT), located in the Himalayas with a diameter of 4 meters, has opened its eyes and looked into the deep universe. It uses a slowly rotating liquid mercury disk instead of a solid mirror to focus light for observation. Compared with traditional telescopes, liquid mirror telescopes are much cheaper to build and have other unique advantages. If ILMT is successful, a larger liquid mirror telescope may be placed on the moon in the future to help observe the "look" of the first star in the universe. The basic concept of liquid mirror telescopes is very simple: if you stir a liquid, its surface will form the shape of a plate, which has proved to be very suitable for focusing light. The concept of liquid mirror telescopes dates back to the 17th century and Isaac Newton, but no attempt was made to build such telescopes until the late 19th century. At the beginning of the 20th century, American physicist Robert Wood made a prototype of a small liquid mirror telescope with a diameter of 5cm. However, Wood encountered many problems in the manufacturing process: ripples were generated in mercury, and it was difficult to make a plate that transferred metal to rotate at a constant speed. In 1982, Elmanor Bora of Laval University in Canada found a solution. In response to the ripples troubling Wood, he suggested that a thin layer of air be pumped between the basin containing mercury and the motor that rotates the mercury to suppress the vibration. He also suggested pouring liquid resin on the surface of the disc to dry it into a suitable shape, and then pouring reflective liquid on it as a coating to reduce the amount of mercury required. After a series of improvements, Bora et al. built a liquid mirror telescope with a diameter of 2.7 meters near Vancouver, Canada, in 1994. Paul Hickson of the University of British Columbia in Canada, in cooperation with the National Aeronautics and Space Administration (NASA), built a 3-meter liquid mirror telescope in New Mexico to observe space debris. At the beginning of the 21st century, the University of British Columbia built an experimental 6-meter zenith telescope on a mountain top outside Vancouver. These projects confirm the idea of many astronomers that liquid mirror telescopes are much cheaper to build than traditional telescopes. Good quality and low price Many researchers say that the cost of liquid mirrors is only about 1% of that of glass mirrors, so it is very suitable for manufacturing large telescopes. ILMT is worth US $2 million and is jointly built by Belgium, Canada and India. Not far from ILMT is another 3.6 meter, maneuverable Devastal optical telescope, which was built by the same Belgian company at the same time, but the price is 18 million dollars. In addition to good quality and low price, LIMT is also very focused. Jean Surd, an astronomer at the University of Liege, Belgium, who is responsible for the ILMT project, said that unlike ordinary telescopes, which can point at different places, liquid mirror telescopes can only look directly at the sky overhead. This was initially considered a serious disadvantage because there was no way to observe specific objects. But Hickson said, "By repeatedly observing the same