Most astronomers are actually astrophysicists. Until the late19th century, astronomy was still difficult to describe and calculate. Astronomers take pictures of celestial bodies through telescopes and calculate some things, such as solar and lunar eclipses, the position of planets and the position and distance of stars. However, astronomers lack a real understanding of the physical properties of stars and the physical mechanisms that control why they glow and how they evolve. Since then, our breakthrough in the knowledge of atomic structure and material action has enabled astronomers to discover the internal working mechanism of the universe through the application of physical laws in many aspects. In this way, most astronomers today are actually astrophysicists, doing astrophysics. This title can impress people at cocktail parties.
Astronomers can be roughly divided into observation astronomers and theoretical astronomers. Although some people do both, most people are more suitable for one of them. Although observation astronomers don't have to bury their heads in observation all day, they need to research and design telescopes and instruments (such as cameras, photometers, spectrometers, etc.). ) to obtain and analyze the data of cosmic objects. On the other hand, theoretical astronomers usually use supercomputers to build models that simulate cosmic phenomena.
The work of observation astronomers and theoretical astronomers is usually complementary. Sometimes, observation astronomers will find unexplained phenomena in the universe, while theoretical astronomers will try to explain their observed phenomena with mathematics and known physical laws. Sometimes, theoretical astronomers will develop a theory to predict the existence of a certain phenomenon or a certain physical state in the universe, and observation astronomers will try to verify the correctness of this theory through observation. The first example is the discovery of pulsars and the later neutron star theory. The second example is the theoretical hypothesis that black holes exist and then they are really discovered.
Generally speaking, studying the universe is a frustrating passive activity. Physicists, chemists and biologists have one thing in common: they can enter the laboratory or reach their destination and effectively create the phenomena they want to study. They can touch it, operate it and contact them directly. Ask a physicist how much a substance weighs, and they can put it on the scale and read it immediately. Ask a chemist how much heat a reaction gives off, and he can measure it with a thermometer. Ask a biologist what the genetic characteristics of a blood sample are, and he can immediately conduct a series of careful tests. For astronomers, the whole universe is a laboratory. However, by definition, the universe "stretches out there", far beyond our direct contact. Although an astronomer can measure the distance of a star from us, he can't verify the distance with a tape measure. The astronomer wants to know the temperature of the surface of the sun, but he can't go to the sun and plug in a thermometer. An astronomer wants to know the composition of a distant galaxy, but he can't take samples there and send them back to Earth for analysis. However, we do know the distance between stars, the temperature of the sun and the composition of distant galaxies. This is why astronomy is such a fascinating field and a kind of talent, which has made such a great contribution to the creative flexibility of human thinking.
Astronomers study the universe by collecting and analyzing the light of cosmic celestial bodies and radiation of other bands. Astronomers can't go to most planets, stars and galaxies in the universe. But to study the universe through the information sent by celestial bodies. What can convey information to us is light and radiation in other bands. In this way, astronomers mainly study cosmic celestial bodies (composed of matter) through celestial radiation. Soon we will talk about radiation. You can also find a section on matter at the end of this chapter.
Optical telescope is a device that focuses light, so we can see weaker objects than what the naked eye can only see. The principle of a telescope is essentially the same. The light entering the telescope is continuously focused into a thinner beam by a series of lenses and mirrors. Because light and radiation are the means for astronomers to study the universe, the more radiation they collect, the more information they can learn.
There are two basic types of optical telescopes. Most of them are either refracting telescopes or reflecting telescope.
Refractive telescopes use a lens system to concentrate light. When I was a child, most people had this experience. On sunny days, we light a leaf or a piece of paper with a magnifying glass. The principle of this experiment is that a magnifying glass focuses the light on the surface to a point, which makes the temperature of this point extremely high, that is, the luminosity is extremely high. Refractive telescopes do the same thing with lens groups. The big end of the refracting telescope has two lenses of the same size but different types. Together, they focus the light on the other end of the telescope when it passes through them. At this time, no matter where the telescope points, it will image.
10 reflecting telescope uses one or more mirrors to accomplish the same thing. In a simple reflecting telescope, a distant light beam falls on a mirror. This mirror is not flat, it is concave. The result will be a focusing effect. A specific shape is a paraboloid, which can focus the incident light parallel to the optical axis at the same point. Like a refracting telescope, distant objects are imaged at this point.
1 1 A simple and ordinary reflecting telescope, which was loved by astronomy lovers and invented by Newton. This design, called Newton reflecting telescope today, focuses light with a concave paraboloid at one end of the lens barrel. For the convenience of observers, a flat mirror is placed at the other end of the lens barrel to reflect light to the side of the lens barrel where the eyepiece is installed. Many astronomy enthusiasts have telescopes of this design.
The 12 refracting telescope with a diameter of several tens centimeters is more expensive than reflecting telescope. For example, an ordinary 15cm reflective telescope costs several hundred dollars, while a 15cm refractive telescope costs several thousand dollars. The reason is that at this size, it is cheaper to grind the mirror for astronomical observation than to grind the lens system.
13 for amateurs who need portability, both refractive telescopes and Newton's reflection are bulky. A typical Newton reflection of 10 inch is about 6 to 7 feet long and weighs more than 100 pounds, while a 6-inch refracting telescope is this big. Obviously, unless you have a fixed place to install these devices, you will face transportation difficulties.
14 Another telescope design called Schmidt-Ka seglin provides an interesting advantage. It is a combination of a mirror and a lens. Schmidt-Karl-seglin model with a diameter of tens of centimeters is far more expensive than Newton model, but cheaper than pure refraction model, and has the advantage that the lens barrel is only one-third of its length when Newton model has similar performance. In this way, Schmitt-Ka seglin model is more portable and can be put in a small and cheap place. Because it is short, it shakes very little when there is wind. This is very important, because the magnifying effect of the telescope, even the vibration caused by a small breeze, will cause great shaking to the image of the telescope.
15 The lower limit of the darkest object we see depends on how much light enters our eyes and is focused. We can see things because light passes through the pupil, is focused on the retina by the lens system in the eye, and the signal is sent to the brain. The more light enters the eyes, the more light falls on the retina, and the stronger the signal sent to the brain, the brighter the object. When we just entered a dark room or just walked outside from a bright environment, we felt that we could not see anything. But when the eyes "adapt", they can see more clearly. Adaptation means that the pupil gradually becomes larger, allowing more light to pass through. However, there are limits. How dark you can see depends on how big your pupils can become.
Telescope 16 can let us see darker objects because they let more light into our eyes. Even in the darkest conditions, on average, the pupil cannot be enlarged more than 8 mm. So we can only see that the darkest light is directly proportional to the brightness of the luminous flux passing through 8 mm square. But telescopes allow us to deceive nature and focus more light into a beam suitable for the size of the pupil. Look at the stars with the naked eye. You can only use a pupil of 8 square millimeters to collect light. Looking at the starry sky with a telescope is equivalent to collecting light with a 250 mm square lens or mirror, which is equivalent to having a pupil with a diameter of 250 mm. No wonder the telescope can let us see things in the universe that are much darker than the naked eye. Understand this basic principle, and you will understand that telescopes can reveal the magical power of the universe known so far. We will see that professional astronomers receive signals not with their eyes, but with instruments far more objective than their eyes. But the location is the same.
17 astronomers tend to call telescopes by the caliber of the primary mirror. Astronomers tend to call telescopes "36 inches" or "2.4 meters". When doing so, they expressed the diameter of the telescope's primary mirror in feet or meters. The primary mirror is usually called the objective lens.
The ability of 18 telescope to show us farther and darker objects depends on the area of the main mirror. Although astronomers call a telescope the diameter of the eyepiece, the ability of the telescope to focus light is proportional to the area of the eyepiece, not to the diameter. According to the formula of circular area, the telescope with 10 foot actually collects four times more light than the telescope with 5 feet. The ability of a telescope to focus light is sometimes called the ability to focus light. But this has nothing to do with the magnification of the telescope.
To enlarge the image in the telescope, you need an eyepiece. Most telescopes bought by astronomy enthusiasts have a set of classified eyepieces. Each eyepiece is usually a small cylinder containing a lens system. Different eyepieces get different magnifications.
In order to calculate the magnification of a specific telescope under a specific eyepiece, you must know the focal length. The objective lens and eyepiece of each telescope have a so-called focal length. It is actually a distance, usually in millimeters. (1 inch equals 25.4 mm) If you have ever burned leaves with a magnifying glass, the distance between the lens of the magnifying glass and the burning object is the focal length. In other words, it is the point where the lens and light from a distance (in this case, the sun) converge. The focal length of the eyepiece is usually written on the side or end of the eyepiece barrel, and the focal length of the objective lens is often included in the telescope literature.
2 1 To calculate the magnification, all you have to do is divide. When you insert a specific eyepiece into a telescope and need to calculate its magnification, all you have to do is divide the focal length of the objective lens by the focal length of the eyepiece. For example, the focal length of the objective lens of a telescope is 2540 mm You insert an eyepiece with a focal length of 25.4 mm, and its magnification is 100. This means that when you pass through this observation plane, you will see objects that are 100 times closer or 100 times larger than what you see with the naked eye.
Theoretically, any telescope can get any magnification. In order to get greater magnification, all you have to do is choose an eyepiece with shorter and shorter focal length. Thus, if an eyepiece with a focal length of 25.4 mm gets a magnification of 100 times, then an eyepiece with a focal length of half, that is, 12.7 mm, can get a magnification of 200 times on the same telescope. An eyepiece with a focal length of 6.35 mm can get a magnification of 400 times. In theory, you can keep doing this until you zoom in a million times or more. But there is a problem, and that is ...
Useful magnification of a telescope. It must be remembered that the eyepiece magnifies the image formed by focusing through the objective lens. All eyepieces need to be magnified by this image, so there is a limit, that is, how much light can work effectively. In short, the more light the eyepiece receives, the larger it can enlarge the image and still produce a bright and clear image on the retina of your eye. In other words, for a particular telescope, there is a practical limit to the clear and bright images you can see. Exceeding this limit will lead to bad results. With the increase of magnification, you do get bigger and bigger images, but they will become darker and more blurred. In fact, it's hard for you to see the details. So it's much more than "What's the magnification of this telescope?" The important question is "What is the maximum useful magnification of this telescope?"
The effective magnification of a particular telescope depends on the size of the primary mirror. Although the useful magnification of a telescope depends on many factors, including the optical quality of the telescope and the stability of the earth's atmosphere at a certain night. In order to get the maximum useful magnification, you should find a telescope, measure its diameter and multiply it by 40 inches. Therefore, the maximum magnification that a 30-foot telescope can obtain at most nights is about 3*40= 120 (also written as 120X), and a 6-inch telescope can see the same clear and bright image at a magnification of 6*40=240 at the same night. So it is worthwhile to buy a telescope with the largest objective as much as possible.
Sometimes, it is wiser to choose a lower magnification than the maximum magnification. The low magnification eyepiece will get a smaller image, but the image will be clearer and brighter. In most cases, this will be more suitable for the eyes. Moreover, for some large celestial bodies, such as star clusters, comets, the moon, etc., the eyepiece with large field of view and low magnification can get better images.
For those who simply enjoy the fun of the sky, binoculars can be regarded as a very satisfactory tool. In order to adhere to the creed of "value for money", binoculars are an affordable choice for us to see the sky through binoculars. Although binoculars can't provide you with the details of the moon and planets that ordinary telescopes can provide, you just lie down and scan the stars casually. They're already amazing. In addition, equipped with binoculars, you can enjoy many wonderful moments, such as cruising along the Milky Way, looking for nebulae and clusters you can see in this book, and observing binary stars, eclipses and unexpected comets.
The numbers on the binoculars tell you its size and magnification. A double cylinder is usually described by two numbers and an x, such as 7×35 or 10×50. The first number of the two numbers represents the magnification of binoculars, and the second number represents the aperture of the main mirror of binoculars, in millimeters. Because 25mm is about one inch, the objective lens of a 10x50 binocular is 50mm or two inches, and the magnification is 10 times.
It is a good choice to use 7×50 binoculars at night. Many people think that the 7×50 binoculars can provide stronger focusing ability than the 7×35 binoculars (which are often used to watch sports events during the day), but they are not cumbersome and troublesome than the binoculars with larger magnification. Binoculars with higher magnification and larger caliber that can provide us with spectacular scenes of the Milky Way galaxy are best supported by tripods to make them stable.
High-quality refractive telescopes and binoculars use coated lenses. These chemical coatings make the lens look blue, and they reduce internal reflection, thus making the instrument produce perfect image quality.
Astronomy enthusiasts can usually tell you the magnification of the telescope they are using, but professional astronomers don't think so. Magnification is a problem that professional astronomers generally don't care about. That's because professional astronomers usually remove the eyepiece from the telescope and use other optical devices on the telescope to focus the light on the CCD, just like being used as part of a camera or photometer or spectrometer. In this case, professional astronomers are interested in the size of the image, the degree of detail they can see, and the wavelength or color of light that can reach the CCD.
3 1 professional astronomers are more interested in the resolution of the telescope than the magnification. Resolution refers to the extent to which a telescope can theoretically let you see details. The fineness of the details can be said that you can tell how small an object is or how close two objects are. The resolution of a telescope is in angular seconds.
The theoretical resolution of the telescope is easy to calculate. The theoretical resolution of an optical telescope measured in angular seconds can be easily calculated by dividing 13 by the aperture of the telescope's primary mirror measured in centimeters. (2.54 cm equals one inch) The theoretical resolution of such a 100 inch (254 cm) telescope is about 0.05 arc seconds. The theoretical resolution of the 200-inch telescope is about 0.025 arcsecond (only 1/36000 of the full moon diameter). In other words, the second telescope only needs 0.025 arc seconds to distinguish two stars in the sky. 100 inch telescope can only treat them as a star. Sharp images are high-quality images, so astronomers want to get the best resolution. This is another reason why astronomers covet the largest telescope aperture possible.
Hello, XXX? Please give me a star map. Just as there are maps of Texas and Afghanistan, there are also maps of the sky. It used to be hand-painted, but now astronomers mainly rely on photos or computer images. One of the most extensive photos and images of this kind consists of southern hemisphere observations made by the Paloma Observatory in California and the European Southern Observatory in Chile. Hundreds of images show the stars in the sky as dark as 20. Another large-scale star map is the catalogue of the Hubble Space Telescope. It contains 15 million stars as dark as15, and can only be obtained from large-capacity optical discs. Before observing, an astronomer may glance at the conspicuous stars around his desired target, which can serve as signposts for his desired target.
Astronomers use a set of methods similar to geographical latitude and longitude to locate objects in the sky. Just as objects on the earth can be represented by latitude and longitude, any object in the sky can be represented by a similar coordinate system, in which declination replaces latitude and right ascension replaces longitude.
35 declination is in degrees. The great circle parallel to the earth equator in celestial coordinates is called the celestial equator. Like latitude, if an object is located north of the celestial equator, it is said to have positive declination. Similarly, objects found in the sky south of the celestial equator also have negative declination. The distance to the north or south is measured in degrees, angles, minutes and seconds (like latitude).
Right ascension is measured in time units. Right ascension coordinates are measured eastward in the sky. Just like longitude, there should be a zero point. Just like the zero-degree meridian passing through Greenwich, England, the zero-degree meridian in the sky is the meridian passing through vernal equinox, and the right ascension of a celestial body is the length of time from when this zero-degree meridian is due south to when the desired celestial body is due south. In this way, the right ascension of celestial bodies is measured in hours, minutes and seconds in time.
A star map usually includes the coordinates of the cosmic objects it contains. Just as a map usually marks latitude and longitude on the side, a star map usually marks right ascension and declination in the area it depicts. Celestial tables and catalogs generally also list the coordinates of each celestial body. Right ascension is generally abbreviated as R.A. Magnetic declination is generally abbreviated as Dec, so, for example, Sirius, the brightest star in the winter sky, can find R.A.6h 14m, DEC.- 16 35' in the sky. The brightest Vega in the summer sky is located in R.A. 18h34m, dec+38 4 1'. These coordinates can be used to locate the positions of stars in the sky conveniently and accurately, just like setting latitude and longitude on a ship in Los Angeles or at sea.
The coordinates of celestial bodies and celestial spheres relative to the movement of stars are constantly changing. Because the sun, moon and planets are constantly moving relative to the stars, their right ascension and declination are also constantly changing. In this way, the table listing their locations needs to be changed every night. Sometimes it is necessary to list the hourly coordinates of a particularly moving celestial body, such as the moon.
Why do astronomers need such a coordinate system? They can't aim the binoculars where they want to see, just like you do with binoculars? There are many reasons why this system is necessary. First of all, many professional telescopes weigh several tons and are difficult to turn. Second, telescopes are usually placed in observatories that can only see one sky, and astronomers usually can't see the whole day. Third, the target stars chosen by astronomers are usually too dark to be seen by the naked eye. Fourthly, if a German astronomer wants to tell his partner in Chile to aim his telescope at only one star they are interested in, he can't just say, aim the telescope there. It doesn't make any sense.
Many telescopes are computer-aided tracking, pointing to the correct right ascension and declination of the celestial body that astronomers want to study. Many professional telescopes and even some amateur mirrors are controlled by computers, which automatically move and point to the correct celestial coordinates. In recent years, some enthusiasts even pre-installed software including the coordinates of planets, bright stars and other beautiful clusters, nebulae and galaxies in their computers. Just enter the name of the celestial body you want to see and press a button, and the telescope will find it for you.
Astronomers don't like twinkling stars. The twinkling stars in the sky are a very romantic sight. Ironically, this is what astronomers are afraid of. That's because when the stars shine, it means that the atmosphere of the earth is not good. Only when the earth's atmosphere is clean and stable can the telescope take very clear images of celestial bodies. But sometimes the earth's atmosphere is extremely unstable, indicating that there are countless turbulence in the atmosphere. Observing celestial bodies through the atmosphere at this time is like looking at the things below through a clean and swift stream. The objects under the stream seem to be constantly fluctuating and distorted by the turbulence of the water flow. Similarly, atmospheric turbulence will distort the light passing through it. To the naked eye, there are almost no stars twinkling in these unstable atmospheres. Telescopes make the problem more complicated, because in the process of magnifying the images of celestial bodies, the atmospheric disturbance is also magnified, and the images of stars are scattered into spots with changing sizes and shapes. Astronomers call the night when the atmosphere is unstable poor visibility. In this way, the resolution of the telescope on a certain night depends on the comparison between atmospheric conditions and its own size.
Astronomers usually try to build the observatory in a place with longer atmospheric visibility. The biggest consideration in choosing the new site of the Observatory is the atmospheric stability of a place or the durability of good visibility. Such places are usually chosen on higher peaks, where the prevailing wind comes from relatively flat terrain or ocean. The airflow generated by this flat terrain can be kept stable and parallel, so that there is only as little vertical movement as possible. Thus, for example, the Kit Peak National Observatory is located on a mountain several kilometers high in the relatively flat Arizona desert. Some of the best observatories in the world are located on a series of peaks, such as Mauna Kea, an extinct volcano in Hawaii, and the Andes in Chile. These are all because the windward side of these places is an endless ocean. However, although in such an ideal place, the resolution of some large telescopes rarely exceeds 1 arc second.
In order to find the place to build the observatory, astronomers are also looking for the clearest place. Understandably, astronomers hope to find not only the place with stable atmosphere, but also the clearest place. This of course means that there are as many sunny days as possible every year. Parts of Hawaii are covered with tropical rain forests, but above 13000 feet, the highest peak of Mauna Kea is so high that it is beyond the "meteorological zone" except for occasional heavy snow. Those observatories in Chile may not see a drop of rain a year in the dry desert.
Another important factor in site selection is to stay away from pollution. This seems obvious, but when it comes to pollution, optical astronomers are not only concerned about the lack of these compounds in the air. What they care about is another form of pollution that others have never thought of, light pollution. City lights and car lights shoot into the sky, washing away the light of the dark galaxy, making some astronomical research almost impossible except in the suburbs. Mount Wilson and Paloma Mountain were the focus of astronomical research in the 20th century, but they have gradually become unusable due to light pollution in big cities such as Los Angeles and San Diego. Even Kit Peak is increasingly threatened by Tucson's expanding population. Astronomers have moved to further mountainous areas, such as Hawaii and Chile.
The public can help reduce light pollution. There is no need to reduce the amount of safe lighting required by streets and expressway at night. The government and the public can take some simple measures to significantly reduce the light pollution they produce without increasing the burden. As long as we add lampshades to street lamps and illuminate expressway with different lights, we can regain the beautiful starry sky, which is not only important for astronomical observation, but also for the decreasing natural resources. To find out what the public should do, please contact:
Dr. David Crawford
Dark sky association
3545 Stewart Street
Tucson, Arizona 857 16 1
When we talk about the study of the universe, we need to pay more attention to what our eyes can notice. Sometimes the sky looks clear, but it is unacceptable for some astronomical research. This is especially true for observational optics, which is a branch of astronomy that accurately measures the apparent brightness of celestial bodies. For example, a thin cloud is actually invisible to the naked eye, which causes great fluctuations in such an instrument, leading to data scrapping.
There is a technical limit to how big a telescope to build. The larger the primary mirror of a telescope, the brighter and clearer the image it forms. So why not simply use a huge mirror? The problem is that the material used to make this kind of mirror has a tolerance limit. In order for the lens or concave mirror of a telescope to focus the light accurately into a clear image, the mirror surface of the lens or concave mirror must have a mirror shape accurate to a few millionths of an inch and only a fraction of the wavelength of light. Modern mirror grinding technology can achieve such accuracy, but when the mirror is heavy enough, it will deform under its own gravity. The deformation is invisible to the naked eye, but it is enough to distort the light and make it impossible to accurately image.
The largest refracting telescope in the world is in Wisconsin, and the largest reflecting telescope is in Russian. (As of 2006, the largest reflective telescope is the GTC telescope of the European Northern Observatory, with the aperture of 1 1.5m- Space Astronomy Network Note). The aperture of the main mirror of the world's largest refracting telescope is1m. It is located at the Yerkes Observatory managed by the University of Chicago, Wisconsin. 1948, a 5-meter-diameter reflective telescope was completed on Mount Paloma, California, USA. It has been the largest in the world for decades. It was not until 1970s that the 6-meter reflecting telescope in the Caucasus Mountains was completed. Unfortunately, its optical system was still not very good.
New materials and technologies have led to the emergence of larger telescopes. An exciting development of telescope design technology in 1980s was that astronomers denied the idea that optical telescopes were limited in size. This concept includes combining several independent lenses into a telescope and making the light received by them produce a joint image. This method makes the total area of a single lens equal to the total area of their combination. The Keck Telescope on Mount Monaque is assembled by 36 lenses with a diameter of1.8m. The test was first carried out at 1990, and the Gemini mirror (Keck 2) next to 1996 was added. The design of a larger multi-mirror telescope is under way.
Other telescope designs use lasers and computers to conquer nature. In a research field called adaptive optics, scientists are studying the use of laser to continuously detect the atmosphere above the telescope and send signals to the computer-controlled motor supporting the primary mirror to accurately change the shape of the primary mirror to offset the turbulent changes in the atmosphere. If successful, this telescope can achieve unprecedented clarity.