If you fly by a helicopter over Pingtang County, Guizhou Province, you will most likely see a silver-white “giant pot” standing between the entire valley, and the surrounding mountains are like shelves supporting the “giant pot”. Seeing this kind of “pot”-like object, our first reaction will definitely feel that it is a signal receiving device. But when I tell you that it is actually a telescope, will you be surprised?
This “Giant Sky Viewing Eye”, the size of 30 football fields, is the world’s largest single-aperture spherical telescope (FAST) with a diameter of 500 meters. 400 years ago, the diameter of the first human astronomical telescope was only 4.2 cm, and the diameter of FAST was 12,000 times that of it. Compared with the 100-meter telescope in Bonn, Germany, which is known as the “largest machine on the ground”, FAST’s sensitivity has increased by nearly 10 times; compared with the American Arecibo 300-meter telescope, which was rated as the top ten projects in the 20th century by mankind, its The overall performance is improved by about 2.25 times. As the world’s largest single-aperture telescope, FAST will maintain the status of world-class equipment in the next 20-30 years and become the head of the telescope family.
Different from our inherent impression of optical telescopes, FAST is a radio telescope. It has neither a tall erected telescope tube nor an objective lens or eyepiece. FAST is composed of an antenna and a receiving system. The antenna is like an eye to a radio telescope, and its function is equivalent to the objective lens in an optical telescope. It collects the weak cosmic radio signals, and then transmits the collected signals to the receiver through a special tube (waveguide) for amplification, and then separates the useful signals from the noise and transmits them to the back-end computer write it down. The recorded results are many curved curves. By analyzing these curves, astronomers can obtain various cosmic information sent by celestial bodies.
As the world’s largest single-aperture spherical radio telescope, how powerful is FAST?
First of all, FAST has a large caliber and can see far. The most important parameter of radio telescope is sensitivity. The higher the sensitivity, the stronger the telescope’s ability to detect weak radios. To increase the sensitivity, it is necessary to expand the aperture of the radio telescope. The caliber of FAST has reached the largest in the world-500 meters. In theory, FAST can receive electromagnetic signals 13.7 billion light-years away, which is close to the edge of the universe.
Secondly, FAST has a flexible “big eye”. According to the working principle of FAST, when it observes the celestial body, it will change with the azimuth of the celestial body. A 300-meter-diameter instantaneous paraboloid is formed in real time on its 500-meter spherical coronal active reflection surface, and the 300-meter paraboloid Converge electromagnetic waves. To put it vividly, if FAST is compared to a huge eye, the diameter of the eyeball of this giant eye is 500 meters, and the diameter of the eyeball responsible for receiving light is 300 meters. FAST relies on this huge and flexible eyeball to gather electromagnetic waves and observe deep space.
Third, millimeter accuracy. The design goal of FAST is to gather the signals covering 30 football fields in a space the size of a tablet, otherwise, it would be impossible to monitor the weak radio signals in the universe. With a structure of 500 meters, the precision requirements of millimeter level are everywhere. There are more than 7000 arm-thick steel cables used to weave the cable net. The processing accuracy of each one is controlled within 1 mm; the final 500-meter diameter antenna accuracy is 3 mm, and the manufacturing accuracy of each small panel is 1.5 Mm.
Finally, FAST can rush out of the Milky Way to find new stars, especially fast-rotating, extremely dense pulsars. FAST may also observe clues in the early universe-the movement of neutral hydrogen cloud clusters, and grasp the details of the interaction between galaxies. Demystifying the origin and evolution of the universe. In a similar way, FAST can also monitor the unique electromagnetic waves emitted by some organic molecules in space, searching for possible interstellar communication signals and extraterrestrial life.
The establishment and use of the FAST radio telescope can extend my country’s space measurement and control capabilities from the moon’s synchronous orbit to the edge of the solar system, which will lay an important foundation for my country’s Mars exploration and other deep space research.
After a major event, people will remember a highly emotional memory, which is called “flash memory.” In these memories, people will not only remember this event, but also remember the environment and inner feelings they were in at that time.
But this kind of memory can easily be altered or false memories appear over time. Taking the 9/11 incident as an example, psychologists were surprised that within one year of the incident, some of the details of the stories remembered by some people (about 40%) changed. Some people said that they saw the process of the terrorist attack on the street with their own eyes. Others said they knew about the incident when they suddenly received a message from a friend. About a year ago, they said that was not the case. Said that those people who saw the incident with their own eyes on the street were watching from a distance in their office. The person who received the friend’s message actually learned of the incident through television. Obviously, their memory was wrong.