Astronomical telescopes are hard to say because they are constantly developing.
In fact, no one knows what the total is.
For us ordinary people, the vast universe is almost immeasurable. For astronomers, it is not only necessary but also possible to draw an accurate map of the universe. The unit of measurement used in astronomy is "light years", that is, the distance traveled by light in a year. The speed of light is about 300,000 kilometers per second, and a light year is about 9.7 trillion kilometers. The diameter of the Milky Way is about 654.38+ million light years. There are other galaxies outside the Milky Way, which are billions of light years away. The newly discovered quasars are located at the edge of the universe that we can observe at present, about 10 to 20 billion light years away from the earth, and are the most distant celestial bodies known so far.
Such a long distance is simply unimaginable. To measure the distance between other planets or nearby stars in the solar system, we can use the parallax calculation method invented by the ancient Greeks. Parallax refers to the angle formed by two lines of sight when observing the same object from two observation positions. In astronomy, the method of measuring parallax is to form a triangle between two observation points and the observed celestial body, know the length of the connecting line between the two observation points (that is, the baseline), and then measure the orientation of the celestial body (that is, the vertex angle of the triangle) from these two observation points, so as to find out the distance between the celestial body and the earth. The longer the baseline, the more accurate the results will be. Usually, when measuring the distance of celestial bodies close to the Earth, such as the moon, radius of the earth can be used as the baseline, and the measured parallax is called "Sunday parallax". If we want to measure the distance of celestial bodies outside the solar system, we usually take the distance from the earth to the sun as the baseline, and the measured parallax is called "annual parallax". Using this parallax method to measure celestial bodies within 8.6 light years is very accurate, and it can also be accurate to 1000 light years.
Another way to measure the distance between stars is brightness measurement. A star may look bright because it is big, active or close to the earth. As long as the actual brightness and visual brightness of the planet are distinguished, the distance between the star and the earth can be accurately measured from the brightness. At the beginning of this century, astronomers used wavelengths to distinguish the brightness of stars and made spectra. They found that different stars have different spectral characteristics. By studying the spectrum of a star with a spectroscope, we can judge the degree of heat and cold of the star. This helps astronomers to distinguish whether a seemingly dim little star is a distant active giant. As long as the light of a star is compared with another star with known distance and similar activity, the distance between this star and the earth can be measured.
More than 80 years ago, most astronomers thought that the Milky Way was the whole universe, and there was nothing outside the Milky Way. However, when more accurate astronomical telescopes were born, this view was proved to be wrong. Those dark spots observed in the past are actually other galaxies, some of which are comparable to the Milky Way, while others are bigger. In the 1920s, American astronomer Edwin Hubble used the world's largest reflective telescope to study galaxies outside the Milky Way in Mount Wilson, California. He analyzed the spectra of these galaxies and found that the wavelengths of various spectral lines shifted to the red end. This phenomenon is called redshift, which means that those galaxies are flying away in the distance. The change of wavelength is the function of Doppler effect, which is the same as the change of the tone of the car horn that is speeding away. With the expansion of the universe, the farther the galaxy is from us, the greater the redshift. In other words, the farther away the galaxy is from us, the faster it will fly away from us. Based on this, Hubble put forward Hubble's law and determined the astronomical measurement unit for calculating the speed of planets-Hubble constant. However, there is a problem with using Hubble constant as a measurement scale, that is, no one knows how long it is.
Astronomers have different opinions on the expansion speed of the universe. The most conservative estimate is that if the distance increases by one million light years, the speed will increase by about16km/s, that is, a galaxy 500 million light years away from us will leave the Earth at a speed of about 8047km/s.. Some astronomers estimate that the speed is twice that. According to preliminary estimates, the farthest celestial body in the universe is about 65.438+0 billion light years away from the Earth. According to the second rate, the edge of the universe is 20 billion light-years away from the earth.
Hubble constant can only be measured in outer space of solar system. There, the expansion rate is so fast that any local influence becomes negligible.
If astronomers can find a "standard candle", that is, a quasar, whose brightness is stable and very bright and can be seen across half the universe, then this problem will be easily solved. But so far, the recognized "standard candle" that can be used in the whole universe has not been found. Therefore, when astronomers use this basic method, they often take a step-by-step approach, that is, set up a series of "standard candles", and each step only plays a role in measuring and determining the next step.