What is the historical significance of astronomical telescope?

Before the invention of the telescope, people could only observe astronomy with the naked eye or with simple tools, so the observation field of vision was greatly limited. 1609, Italian scientist Galileo saw the strange craters on the moon for the first time with a self-made telescope that can be magnified 30 times, discovered four large satellites of Jupiter, and observed the profit and loss changes of sunspots and Venus, as well as the wonderful phenomena that have never been seen in the Milky Way. Since then, telescopes dedicated to astronomical observation have developed rapidly.

Astronomical telescopes, like ordinary telescopes, can bring distant scenery to the eyes of observers. Astronomical telescopes are not only much larger than ordinary telescopes, but also much more precise. Modern astronomical (optical) telescope folding reflecting telescope.

There are many varieties, which can be roughly divided into three categories according to the design principle:

The first is a refracting telescope. This kind of telescope is the earliest telescope used. Its front end takes one or a group of convex lenses as the objective lens, and the back is the eyepiece. Light comes in from the front and goes out from the back. This kind of monocular telescope has a long focal length and is most suitable for astrometry. The first astronomical telescope, galileo telescope, was a refracting telescope. At present, the largest refracting telescope in the world is the telescope with the aperture of 102 cm at the Yekeshi Observatory in the United States.

The second category is reflecting telescope. Due to many defects of early refractive monocular, the scenery you see is often distorted, and there is always a colorful halo around the scene, which affects the observation accuracy. In order to overcome these shortcomings, Newton invented the reflective telescope. Based on the reflection principle, this telescope uses concave mirror as the objective lens to reflect and gather the light emitted by celestial bodies, which not only has high imaging quality, but also has the advantages of short lens barrel and simple manufacturing process. So most modern large astronomical telescopes belong to this type. At present, the largest astronomical telescopes in the world are the telescope with a diameter of 6 meters on Mount Caucasus and the telescope with a diameter of 5? 08 meters in reflecting telescope. The lens glass of the latter weighs 20 tons and can be used to glimpse dark stars such as 2 1.

The third category is the folding reflecting telescope, designed by German optician Schmidt. This kind of telescope combines the advantages of the first two kinds of telescopes, with large field of view, strong light and small aberration, and is most suitable for studying celestial bodies with observation surfaces such as the moon, planets, comets and nebulae.

1On April 24th, 990, the American space shuttle Discovery successfully lifted off from Cape Canaveral. On 25th, it sent the world's most complex space telescope into a circular orbit 6 10 km above the earth (1967, 10, the United States launched a space observatory orbiting the sun). This space telescope is a large space telescope jointly developed by NASA and the European Space Agency. Originally scheduled to serve in the mid-1980s, it was postponed due to the explosion of the space shuttle198665438+1October 28th.

This space telescope is named after American astronomer Edwin Pi Hubble to commemorate his creative work and outstanding contribution in galaxy astronomy, cosmic structure and expansion theory.

Hubble Space Telescope

Hubble Space Telescope is the largest and most advanced space-based astronomical telescope in history (most astronomical telescopes are located in land observatories, called ground-based astronomical telescopes). Its shape is cylindrical, with a length of13m and a diameter of 4? 5 meters, the total weight 12 tons, and the length of both sides 12 meters. From a distance, the Hubble Space Telescope looks like a giant skyhawk trapped in space. Hubble Space Telescope is mainly composed of optical telescope device, safeguard system and scientific instruments.

Optical telescope device is the heart of space telescope, which mainly includes 2? 4 m primary mirror diameter 0? The accuracy of 3m secondary mirror and its supporting structure, primary mirror and secondary mirror is an important part to determine the performance of space telescope.

After the light enters the space telescope from the hatch, it hits the main mirror first and then reflects to 4? Secondary reflector at 5 meters; Then, the secondary mirror reflects the light from a hole in the center of the primary mirror to the scientific research instrument for recording and imaging.

The safeguard system is the main equipment of the Hubble Space Telescope, including information transmission, temperature monitoring, position adjustment and power supply. Information transmission is completed by mirror radio system and geosynchronous communication satellite. The position adjustment is realized by sensing the pitch and yaw information of the telescope through the precision guidance sensor on the mirror surface and sending it to the position control device, which can ensure the position of the telescope to be stable at 0? Within 007 arc seconds, make its direction drift less than 0? 007 arc seconds, to ensure the observation of scientific instruments. There are large rectangular solar panels on both sides of the telescope, which directly convert solar energy into electric energy for the telescope. Scientific instruments are the creators of a series of new achievements of Hubble Space Telescope, mainly five. Among them, dark celestial camera, dark celestial spectrograph, high-resolution spectrograph and high-speed photometer are as big as a telephone booth. They are all placed behind the main mirror at the back of the telescope, close to the focusing surface of the secondary mirror, and receive the light reflected from the secondary mirror. The fifth is a wide-angle planetary camera, which is placed on the circumferential wall behind the telescope. They share an optical mirror system.

The dark celestial camera is the most important scientific instrument in the telescope. As the name implies, it can capture some distant celestial bodies with unclear and dim light and record the observed situation. It magnifies pixels through the camera's optical converter to improve the resolution. The converter first reduces the viewing angle of the pixel detector, then detects it with an image intensifier, and then amplifies it and sends it to the terminal screen to form a corresponding bright spot; Then, the scanning light spots on the screen are recorded by the film camera and stored in the electronic computer, and finally an image is formed.

The spectral spectrograph of dim and weak celestial bodies is mainly used to measure the chemical composition of dim and weak celestial bodies. It can be made into spectral negatives through special gratings and filters.

By analyzing these spectral negatives, we can not only get the chemical composition data of the light source, but also get the temperature, motion and physical characteristics of the light source.

High-resolution spectrograph is used to measure the ultraviolet radiation around interstellar and stellar objects, so as to study the physical composition of explosive galaxies, interstellar gas clouds and the escape of stellar matter.

High-speed photometer is the simplest scientific instrument in space telescope. It can measure the extremely bright light emitted by celestial bodies; But also can be widely used for precise measurement at the microscopic level; The distance of the target celestial body can be obtained by measuring the sum of the light received from the target celestial body. This photometer will play a greater role in accurately measuring the Milky Way and other nearby galaxies.

Wide-angle planetary camera consists of two independent cameras installed in an instrument box, which is mainly used for observing planets. Because of its wide field of vision, it can observe a larger space and provide more exquisite images of stars, and the images of planets obtained are as clear as those taken at close range. Most of the structural equipment of Hubble Space Telescope photographed by Hubble Space Telescope was contracted by many manufacturers, universities and scientific research units led by Lockheed Missile Space Company of the United States, while the European Space Agency contracted the development of solar panels and dim celestial cameras. The cost of the telescope is $654.38 +0.5 billion, and the annual maintenance cost is $200 million. Can work in space for 654.38+0.5 years.

Space photographed by Hubble Space Telescope

Hubble Space Telescope is essentially a large astronomical satellite, just like a space observatory. Because it works in the universe outside the earth's atmosphere, it eliminates the obstacles of astronomical observation on the ground; The absorption of celestial spectrum by the atmosphere and the influence of atmospheric turbulence on celestial observation are avoided. This environmental advantage has greatly improved the performance of the Hubble Space Telescope.

At Goddard Space Center, scientists tested the sensitive detection ability of Hubble telescope, which is equivalent to observing 1? A firefly in Sydney 60,000 kilometers away. Hubble space telescope can detect several times weaker light than ground-based telescope, which is equivalent to seeing the flash of two flashlights on the moon on earth. Its resolution is 10 times higher than that of current ground telescopes.

Edward Weller of NASA said that the ground telescope can see stars of 65.438+billion light years, while the Hubble Space Telescope can see stars of 65.438+billion light years, which allows scientists to see immature stars in the universe because they are also between 65.438+billion and 20 billion years old. What is even more surprising is that this telescope can see the light emitted by celestial bodies hundreds of millions of kilometers away, so it can let scientists know what the light looks like before it reaches the earth. For example, it takes about 8 minutes for light to travel from the sun to the earth. With the Hubble Space Telescope, scientists will know how light is emitted from the sun.

Scientists believe that this is another amazing telescope device in astronomy since Galileo used his own telescope to observe celestial bodies 400 years ago. It will open a new chapter for human beings to explore the universe and let them know a series of little-known mysteries. Scientists hope that it will help to answer a series of scientific questions such as the formation and evolution of the universe and whether there are intelligent creatures outside the earth.

In order to ensure the normal and effective operation of space telescope in space, there must be multi-party cooperation between the ground and the air. For this reason, a large system including space shuttle, space telescope, tracking and data relay satellite and earth station has been formed, which are indispensable.

Space shuttle is the only vehicle for space telescope, which mainly undertakes the tasks of launching telescope into orbit, replacing on-orbit instruments and equipment, overhaul and recovery. Tracking and data relay satellite is a communication satellite in geostationary orbit, which was launched into orbit by American space shuttle Challenge. It undertakes the relay transmission task of information in the space telescope system, that is, it forwards the data observed by the telescope to the ground and the tracking and remote control information of the earth station to the space telescope. The two tracking and data relay satellites needed by the space telescope system were launched into orbit by the American Space Shuttle in the middle and late 1980s, which were located at 4 1 and 170 degrees above the equator respectively. The two satellites are connected to an earth monitoring station, which enables the Hubble Space Telescope to keep in touch with the ground for 85% of its operation time.

The Space Telescope Operation and Control Center located at Goddard Space Flight Center of NASA controls the orbit of Hubble Space Telescope around the Earth to prepare for observing and exploring the universe. First of all, the solar panel of the telescope should be turned on to provide the necessary energy for the normal work of each system on the mirror. If the remote deployment of solar cells fails, astronauts on the space shuttle can use the manual rocker to open it; If the telescope cannot be used for some reason, it can be put back in the cargo hold of the space shuttle and brought back to the ground for maintenance. If all parts of the telescope work normally, the whole space telescope system can start to run on the Internet, and the space telescope can continuously transmit a large amount of information observed by itself to the earth station through a tracking and data relay satellite.

On May 20th, Hubble Space Telescope opened its electronic eyes to observe the universe for the first time and took the first historic space photo.

At 15 GMT 12, when the Hubble Space Telescope flew over Jayapura, New Guinea, the wide-angle planetary camera started at 1 sec and took the first black-and-white photo. Then start the camera shutter again, expose for 30 seconds, and take the second photo. The first photo was taken of NG3532 cluster in the Milky Way, which is about 1260 light-years away from the Earth. It is a difficult cluster to distinguish. The second photo was taken by the sun. These two photos were first stored on tape, and then forwarded to the ground more than two hours later.

The first images of Hubble Space Telescope were processed by computer, and the resolution was 2 ~ 3 times higher than originally expected. Although the second photo with dozens of suns is shown, the image is slightly elongated, but the quality of this photo is better than originally expected without completing the focusing of the telescope optical system.

The orbital period of Hubble Space Telescope is 97 minutes, that is, it orbits the earth once every 97 minutes, and the sunrise is less than 15 times a day, and it enters and exits the earth's shadow area 15 times.

Learning point

geostationary orbit

Geostationary orbit, also known as geostationary orbit and geosynchronous transfer orbit, refers to the circular geosynchronous orbit of satellites or artificial satellites perpendicular to the equator of the earth. Because satellites or artificial satellites orbiting the earth in this orbit are always located in the same position on the earth's surface, observers on the surface can observe them in the same position in the sky at any time and find them motionless in the sky.