1. The history of the development of telescopes
One day in the early 17th century, Hans Lippershey, the owner of an optical shop in a small Dutch town, inspected the ground lenses. Mass, put a convex lens and a concave mirror in a line, look through the lens, and find that the church tower in the distance seems to be getting bigger and closer, so I accidentally discovered the secret of the telescope. In 1608, he applied for a patent for the telescope he made and complied with the authorities' requirements to build a pair of binoculars. It is said that dozens of opticians in the town claimed to have invented the telescope, but Liebersch is generally believed to be the inventor of the telescope.
News of the invention of the telescope quickly spread throughout Europe. After learning about the news, Italian scientist Galileo Galilei made his own one. The first telescopes could only magnify objects 3 times. A month later, the second telescope he built could magnify 8 times, and the third telescope could magnify 20 times. In October 1609, he built a telescope that could magnify 30 times. Galileo used a homemade telescope to observe the night sky and discovered for the first time that the moon's surface was rugged, covered with mountains and had cracks in craters. After that, he discovered the four satellites of Jupiter and the sunspot movement of the sun, and concluded that the sun is rotating. Almost at the same time, the German astronomer Kepler also began to study telescopes. He proposed another astronomical telescope in "Refraction". This telescope was composed of two convex lenses. It was different from Galileo's telescope and had a wider field of view than Galileo's telescope. But Kepler did not build the telescope he described. Scheiner first made this kind of telescope between 1613 and 1617. He also followed Kepler's suggestion and made a telescope with a third convex lens, turning the inverted image of the telescope made of two convex lenses into an upright image. . Scheiner built 8 telescopes and observed the sun one by one. No matter which one, he could see the same shape of sunspots. Therefore, he dispelled many people's illusion that sunspots may be caused by dust on the lens, and proved that sunspots are indeed observed. Scheiner installed special light-shielding glass when observing the sun, but Galileo did not add this protective device. As a result, he injured his eyes and was almost blind in the end. In order to reduce the chromatic aberration of the refracting telescope, Huygens of the Netherlands built a telescope with a tube length of nearly 6 meters in 1665 to explore the rings of Saturn. Later, he also built a telescope with a length of nearly 41 meters.
Telescopes that use lenses as crop mirrors are called refracting telescopes. Even if the lens tube is lengthened and the lens is precisely processed, chromatic aberration cannot be eliminated. Newton once believed that the chromatic aberration of refracting telescopes was irremediable, but later proved to be too pessimistic. of. In 1668, he invented the reflecting telescope, which solved the problem of chromatic aberration. The first anti-telescope was very small. The diameter of the reflector inside the telescope was only 2.5 centimeters, but it could already clearly see the moons of Jupiter and the phases of Venus (see attached picture 1). In 1672, Newton built a larger reflecting telescope and gave it to the Royal Society. It is still in the library of the Royal Society. In 1733, the Englishman Hal made the first achromatic refractor telescope. In 1758, Paul Land of London also made the same telescope. He used glasses with different refractive indexes to make convex lenses and concave lenses respectively, and the colored edges formed by them canceled each other out. But it is not easy to make a very large lens. Currently, the largest refracting telescope in the world has a diameter of 102 centimeters and is installed at the Ardis Observatory. In 1793, William Herschel of England made a reflecting telescope. The diameter of the reflecting mirror was 130 centimeters, made of copper-tin alloy, and weighed 1 ton. The reflecting telescope made by William Parsons in England in 1845 had a reflector diameter of 1.82 meters. In 1917, the Hooker Telescope was built at Mount Wilson Observatory in California, USA. Its primary reflector has a diameter of 100 inches. It was using this telescope that Edwin Hubble discovered the astonishing fact that the universe is expanding.
In 1930, the German Bernhard Schmidt combined the advantages of refracting telescopes and reflecting telescopes (refracting telescopes have small aberrations but have chromatic aberration and are more expensive the larger they are, while reflecting telescopes have no chromatic aberration, are low-cost and can be made very large). , but with aberrations) were combined to create the first catadioptric telescope.
Reflecting telescopes developed rapidly in astronomical observations after the war. In 1950, a 5.08-meter-diameter Hale reflecting telescope was installed on Palomar Mountain. In 1969, a 6-meter-diameter reflector was installed on Mount Pastukhov in the northern Caucasus of the former Soviet Union. In 1990, NASA launched the Hubble Space Telescope into orbit. However, due to a mirror failure, the Hubble Telescope did not begin to fully function until astronauts completed space repairs and replaced the lens in 1993. Because it is not interfered by the Earth's atmosphere, Hubble's images are 10 times clearer than those captured by similar telescopes on Earth. In 1993, the United States built the 10-meter Keck Telescope on Mauna Kea, Hawaii. Its mirror is made up of 36 1.8-meter reflectors. In 2001, the European Southern Observatory in Chile completed the development of the "Very Large Telescope" (VLT), which consists of four telescopes with an aperture of 8 meters and has a light-gathering capacity equivalent to that of a 16-meter reflecting telescope. Now, a group of telescopes under construction have begun to attack the white giant brothers on Mauna Kea. These new contenders include the 30-meter California Extremely Large Telescope (CELT), the 20-meter Giant Magellan Telescope (GMT) and the 100-meter Extremely Large Telescope (Overwhelming Large Telescope, referred to as OWL). Their advocates point out that these new telescopes will not only provide images of space that are far better than Hubble's images, but also collect more light to study the initial state of stars and cosmic gas when galaxies formed 10 billion years ago. Learn more about the situation and see clearly the planets around distant stars.
2. Galileo invented the astronomical telescope. The first person to propose a reflecting telescope was the British mathematician J. Gregory; the first person to build the first reflecting telescope was the British scientist Newton.< /p>
A telescope that uses a reflector to create a telescope. An important feature of the optical performance of reflecting telescopes is the absence of chromatic aberration. Others
Although aberrations can be eliminated in theory, the process is complicated. In order to avoid aberrations, the field of view of practical reflecting telescopes is generally relatively small. The field of view can be expanded through image field correction lenses
< p>field. The material of the reflector requires a small expansion coefficient, low stress and easy grinding. The mirror surface is usually coated with aluminum and has good reflectivity in both the infrared and ultraviolet regions. Reflecting telescopesgenerally have shorter tubes for easier support. Modern high-tech reflecting telescopes also have mirror adaptive optical systems and active optical systems, which can compensate for atmospheric disturbances and deformation and jitter caused by mirror stress
and wind.
Commonly used in reflecting telescopes are the main focus system, Newtonian system, Cassegrain system, Gregorian system, folding axis system, etc. Through the transformation of the mirror, it can be used on the same telescope
To obtain the main focus system (or Newton system), Cassegrain system and folding axis system respectively. The focuses of these systems are respectively called primary focus, Newtonian focus, Cassegrain focus, Gregorian focus and folded axis focus. When one of the above systems is used alone as a telescope, it is called a Newtonian telescope, a Cassegrain telescope, a Gregorian telescope, and a folding-axis telescope. Large optical reflecting telescopes are mainly used for astrophysics research, especially spectrometry, photometry and photography of faint celestial objects.
China’s current largest optical telescope is 2.16 meters. The current largest telescope in the world is the Keck Telescope in Hawaii, with a diameter of 10 meters. It is composed of 36 1.8-meter hexagonal mirrors and costs a 130 million U.S. dollars
It was mainly built with donations from Keck, an American entrepreneur. After the first Keck telescope was successfully built, the Keck Foundation invested in the construction of Keck II. Telescopes, two next to each other, are extremely powerful; other large telescopes include the two eight-meter telescopes of the National Astronomical Observatory of the United States in the northern and southern hemispheres, one in Hawaii and one in Chile, collectively known as the Gemini telescopes ;The Japanese built an eight-meter telescope called the Pleiades
in Hawaii; the European Southern Observatory will build four eight-meter telescopes in the next century, with a combined aperture equivalent to 15 meters!