The observational astronomy is that part of the field of astronomy , the celestial bodies by their coming to earth radiations studied and particles. Similar to so-called remote sensing , the focus of the measurement methodology is the electromagnetic radiation of distant objects in the entire range of the spectrum , from radio waves to infrared , visible light and ultraviolet radiation to X-rays and gamma rays. The direction of incidence and the physical properties of the radiation allow conclusions to be drawn about the properties of the emitting or light-absorbing celestial objects.
Precise measurements of the direction provide information on the position and distance, movement and structure of the celestial objects in question, while studies of the spectrum point to the chemical composition, star temperature , magnetic fields and changes in distance to the observer. With a photometer the luminosity of stars can be determined, from their temporal change their equilibrium status. In addition to electromagnetic radiation, the cosmic particles detectable on earth provide further information. For the future, the detection of gravitational waves promises new types of observations on celestial objects such as neutron stars or black holes .
A central concern of observational astronomy is the development of suitable instruments and detectors. The electromagnetic radiation is captured with the help of telescopes and recorded photographically or electronically. Photometry and digital astrophotography enable the measurement of brightness, spectroscopes by evaluating planetary, nebula and star spectra are important parameters of astrophysics . Telescope constructions specially adapted to the properties of X-ray or radio radiation allow the investigation of these sections of the electromagnetic spectrum. The detection and closer examination of particles and gravitational waves require special detectors.
Astronomy is at a disadvantage compared to other natural sciences in that it cannot examine its objects of investigation under controlled conditions in the laboratory. A direct investigation is only possible for the celestial objects closest to us, in particular the moon and those planets and planetary moons that have already been visited by earthly space probes or whose fragments occasionally fall to earth (e.g. Mars meteorites ). Astronomy is therefore largely dependent on observation, in particular on the evaluation of the electromagnetic radiation that reaches us from distant celestial bodies. On the other hand, it offers physics the opportunity to research extremely high-energy processes that would never be possible on earth.
In view of their special situation, astronomers have developed techniques with which systematic conclusions can be drawn about the properties and development of astronomical objects from observation alone. A large number of visible examples are typically available for each type of observation object. For example, instead of following the evolution of a single star over billions of years, astronomers can observe different stars in different stages of development in order to investigate the evolutionary path of the stars. With the help of the cosmological principle , conclusions can be drawn about the behavior of distant objects from investigations on closer sample objects.
There are various ways of defining sub-areas of astronomy. The term "observational astronomy" is used as a collective term for the various techniques of astronomical observation. There is no common name for its counterpart, the formulation and research of physical models, through which the properties of celestial objects can be traced back to the known physical laws. Theoretical astrophysics is most likely to play this role , in which this type of modeling occupies a large area, although it also partly deals with the theoretical basis of astrophysical observation techniques and thus overlaps with observational astronomy.
If sub-areas of astronomy are defined using the objects to be observed, there is always an overlap with observing astronomy - solar research, for example, naturally includes the corresponding specialized observation methods; The same applies to planetology , stellar astronomy , astroparticle physics and the other thematic sub-areas. The names for those sub-areas of observational astronomy that are named after the areas of the electromagnetic spectrum in which the observations take place: radio astronomy , infrared astronomy , optical astronomy , ultraviolet astronomy , X-ray astronomy and gamma astronomy have a wider distribution than the generic term .
Before the invention of the telescope
The beginning of observational astronomy cannot be clearly established. Some cave paintings 20,000 years ago could show some kind of constellation. The ancient Egyptians began using A calendar based on observations of the star Sirius . Astronomical records are known from many advanced civilizations, for example the Mayans and the Assyrians .
Star brightness and simple instruments for determining the position of celestial objects can already be found with Hipparchus and Ptolemy in the first millennium before our era; they were used in a more refined form in Arabic astronomy in the first millennium AD. The observation devices used by Tycho Brahe in the 16th century were based on the same principles . Mechanical computers such as the astrolabe , which also found its way from the Greeks via Arabic astronomy to medieval astronomy, made it possible to determine the time and predict astronomical events such as sunrise.
17th to 19th century
Beginning with the first documented astronomical use of a telescope by Galileo in 1609, the history of observational astronomy largely follows the development of increasingly powerful telescopes. Milestones were, for example, the development of the reflector telescope by Gregory , Cassegrain and Newton and the construction of ever larger reflector telescopes by Herschel in the 18th century or Parsons in the 19th century, up to Hale's 100-inch telescope (1917) on Mount Wilson Observatory .
In parallel with the technical development of optics and the assembly of telescopes, there were other important advances: From the early 19th century, spectroscopy found its way into observational astronomy. As early as 1800, Herschel was using a prism and a thermometer to prove the thermal effect of the sun's rays - the beginning of infrared astronomy . A few years later, Wollaston and Fraunhofer discovered the spectral lines in the solar spectrum. In 1852 Stokes published the first observations of ultraviolet sunlight. In the middle of the 19th century, Bunsen and Kirchhoff deduced the chemical composition of the sun from these lines. From then on, the development of more and more accurate astronomical spectrographs began. From the end of the 19th century, the use of photographic methods gave the field a new direction and enabled observations of previously impossible accuracy and sensitivity.
20th to 21st century
Characteristic of the 20th century was the introduction of electronic measuring and detection instruments and the expansion of systematic observations to other wavelength ranges of the electromagnetic spectrum. With the observations of Jansky and Reber , radio astronomy began in the 1930s, which experienced a boom after the end of the Second World War, thanks to decommissioned military radio and radar systems. In the 1940s, photomultipliers were used for the first time to determine brightness, followed by first attempts at electronic image acquisition, and finally by the CCD detectors that are still used today .
For observations in wavelength ranges that are filtered out by the earth's atmosphere, the advance into space began: for the first time in 1946 for ultraviolet observations, with a V2 rocket captured by the Americans from the Nazi Germans , and in 1949 in the same way with the first X-ray observations outside the atmosphere . From 1970, Uhuru, the first X-ray satellite, orbited the earth, followed in 1983 by IRAS , the first infrared observatory. With the Soviet Lunik 1, a space probe explored another celestial body, the moon, for the first time in 1959; Landings and first pictures of the back of the moon followed in the same year. In 1962, Mariner 2 was the first probe to reach another planet, Venus ; In the decades that followed, other probes reached all of the major planets in the solar system.
The astroparticle physics began in 1912 with the ballooning of Victor Franz Hess , where this first sign of ionizing radiation found in the cosmos. However, it was only in the course of the following decades that it became clear that these were fast elementary particles. With the development of better and better particle detectors, more and more accurate measurements of cosmic rays became possible. In 1983 the construction of large neutrino detectors began, with which solar neutrinos and with the neutrinos of the Supernova 1987A also for the first time neutrinos originating from outside our solar system were detected.
Modern developments in observational astronomy aim at increased precision, even better utilization and linking of the various areas of the electromagnetic spectrum, as well as the collection of ever larger amounts of basic data on stars in the Milky Way and galaxies in the universe. This includes new satellite observatories such as the Hubble space telescope , the development of technologies such as active and adaptive optics and, for example, the construction of highly sensitive gravitational wave detectors , which are intended to open up a completely new mode of observation. Large projects like LOFAR place great demands on the computer infrastructure, both in terms of transport and in terms of processing and storing the collected data.
Sky observations were certainly made as early as the Stone Age , because some cave paintings contain hints of constellations . From Mesopotamia from the 3rd millennium BC BC many astronomical notes and measurements by priest astronomers , among others. for purposes of calculating planetary orbits, conjunctions and for astrology . In ancient Greece, star maps and exact position catalogs were created and a scale for star brightness was developed.
In classical astronomy (until around 1850), observations of the sky were limited to visual methods, for which, in addition to high-quality telescopes and sufficient experience of the observer , several external factors and special properties of the eye are essential - see astronomical observation with the eye . Towards the end of the 19th century, research increasingly shifted to astrophotography and spectroscopy , to which radio astronomy came around 1950 and, from around 1980, infrared and UV light, X-ray astronomy and very light-sensitive CCD sensors .
Evidence of objects and their structure
The basis of any observation is to first detect a celestial object . In many cases, however, it is already possible to perceive structures on the object when it is discovered. The next step is generally to determine its celestial coordinates by taking directional measurements, followed by measuring brightness , color and spectrum.
Many stars are already visible in the night sky with the naked eye . The patterns that they form on the celestial sphere, called constellations or constellations, assign the stars involved an approximate position and facilitate orientation in the sky. The oldest of today's constellations , established by the International Astronomical Union, go back to the twelve Babylonian signs of the zodiac . However, according to today's understanding, these patterns are random ( apart from individual rows of stars ) and do not allow any conclusions to be drawn about the properties of the stars involved.
From today's perspective, those historical observations with the naked eye that relate to ephemeral celestial phenomena are particularly interesting. Ancient records of new stars suddenly appearing give evidence of so-called novae (the flare-up of one of the partners in a binary star system) or supernovae (explosions at the end of the life of a massive star). Reports of passing stars, often interpreted as omen , or their depiction on coins , for example , indicate the appearance of comets .
Because of their great distance, celestial objects are often very faint when observed from the earth; to observe them, as much as possible of their light has to be collected. In addition, the details of their structure are very close to one another from an earthly perspective; in order to be able to prove the structure anyway, a high resolution is necessary. Both requirements are met by telescopes whose large lenses made of optical lenses and possibly mirrors far exceed the capabilities of the human eye. With telescopes it is possible to determine the surface structure of the planets and other bodies of our solar system, to separate the components of closely spaced binary stars , to map extensive structures such as nebulae and even to detect the details of galaxies millions of light years away - some of them even single stars .
From around the 18th century, the observed objects were systematically recorded in catalogs . The best-known catalogs are the Messier catalog and the New General Catalog (as well as the Index Catalog supplementing the NGC ).
A direct visit is only possible for the closest astronomical objects - the earth's moon and selected planets and their moons - where a space probe can observe and measure the object from close up or even land on it. Well-known examples are the Pioneer probes as well as Voyager 1 and Voyager 2 .
Position in the night sky
The position of an object in the night sky is a fundamental observation variable. It can be specified in the context of various astronomical coordinate systems. The basic principle of determining position in the night sky is to measure suitable angles . One example is the so-called elevation angle , the angle between the straight line connecting the observer and the celestial object and the horizon . The determination of position in the sky, the astrometry , has a multitude of scientific applications and lays the basis for almost all further measurements on celestial objects.
The positions of celestial objects, measured by an observer on the earth, change due to the rotation of the earth, but also, for example, due to the movement of the earth around the sun. Periodic changes of this kind are the basis of the calendar calculation and have long been the basis for all types of time measurement: Until 1956, the length of a second was defined as the mean length of a solar day, then until 1967 based on the orbit of the earth around the sun (so-called Ephemeris second ). Only since 1967 has the second been defined in the SI system of units via the properties of certain radiation emitted by atoms of a specific type.
Conversely, the position of the celestial objects can be used to determine the location of the observer. This is the basis of astronomical navigation, in which the geographical latitude and longitude of the observation location are determined by measuring sun or star locations with the sextant .
The development of ever more precise instruments for determining position enabled steady progress in observations. Even simple bearings make it possible to record the position of the sun at the times of the solstice . Even without telescopes, the Danish astronomer Tycho Brahe was able to make systematic observations of the positions of the planets known at the time, on the basis of which Johannes Kepler later established the laws of planetary motion named after him .
With the advent of ever more powerful telescopes, it was possible to measure important astrometric quantities from around 1800 . This includes, for example, the aberration , which expresses the influence of the earth's movement on the apparent star location, and the parallax, which is so important for measuring the distance of distant objects : depending on the observation location (e.g. orbital position of the earth in winter compared to that in summer), closer ones move Stars in perspective against the background of the distant stars. It was also possible to determine the proper motion of stars, which because of the huge distances only show themselves in very small changes in the star coordinates . Exact investigations of the known planetary orbits led to the detection of orbital disturbances , which indicated the existence of other celestial bodies. This led to the discovery of the planet Neptune and (indirectly) the dwarf planet Pluto . An otherwise unsatisfactory explainable anomaly in the orbit of Mercury ultimately turned out to be an effect of the general theory of relativity developed by Albert Einstein .
With the advent of photographic methods, techniques became possible in which the relative distances of different objects are determined directly on the photographic plate or from electronic image data. The latest state of the art are astrometry satellites such as the Hipparcos mission, which determined over a million star locations, and the successor mission Gaia . With modern measurements, the accuracy is so high that the effects of the relativistic light deflection have to be included in the evaluation . One of the goals is to detect the tiny tumbling movements of stars that are orbited by their own planets with similar masses and orbits as Jupiter or Saturn , and thus to discover tens of thousands of new planets distant stars ( exoplanets ).
Using photometric methods , the brightness of astronomical objects can be recorded quantitatively. How bright an object appears when viewed from the earth ( apparent brightness ) depends on the one hand on its intrinsic brightness, called absolute brightness or luminosity in astronomy , and on the other on its distance from the earth. If the absolute brightness is known, the distance can be deduced from the apparent brightness. Objects with which this is possible are called standard candles ; the most important examples are so-called Cepheid stars and type Ia supernovae .
Conversely, where the absolute brightness can be determined from distance and apparent brightness, conclusions can be drawn about object properties. The so-called luminosity classes of the stars are one of the decisive variables in the systematic recording of this type of object. Your system is a modern theories of the column to stellar structure and - genesis . The great brightness of the so-called quasars , combined with the small size of these objects, showed that the quasar luminosity must be generated by an extremely effective radiation mechanism. The only mechanism of suitable effectiveness is the incidence of matter on an extremely compact central object. Corresponding considerations led to the modern image of black holes as the energy source of quasars and other active galaxy nuclei .
Changes in brightness also allow conclusions to be drawn about the nature of the observation object. So-called photometric double stars, for example, cannot be observed separately in the telescope; the light curve - the temporal variation of the brightness - shows, however, that here one star regularly moves in front of another. Information about the orbit of binary stars, in turn, can be used to calculate the mass of each of the partners, or at least the total mass. Other periodic fluctuations in brightness of variable stars correspond to star pulsations in which the star periodically becomes larger and smaller again.
The astronomical spectroscopy is one of the pillars of observational astronomy. Spectral lines - emission lines and absorption lines - with their wavelengths characteristic of the different types of atoms allow insight into the chemical composition of most celestial objects. The strength and shape of the spectral lines also provide information about the physical conditions (e.g. temperature or pressure ) in the observed objects.
Together with the division into luminosity classes , the division of the stars into spectral classes enables them to be classified in a so-called Hertzsprung-Russell diagram . This systematics led to the modern models of star formation and evolution . In general, a comparison of the brightness of an object at different wavelengths provides information about its temperature and, according to the laws of radiation, also about how much radiation the object emits per unit area. The metallicity of a star reflects the composition of the interstellar medium from which the star was formed. Since stars gradually produce heavier elements through nuclear fusion (so-called stellar nucleosynthesis ) and release them back to the interstellar medium towards the end of their lifespan, its metallicity increases in the course of the galaxy's history. Systematic measurements of the metallicity of stars led to the concept of star populations and provide clues about the structure and evolution of the Milky Way.
The spectral lines can also be used to determine whether the spectrum of a distant object is shifted overall. One example is the Doppler effect , the frequency shift due to the movement of an object that allows at least part of the speed of a distant object to be measured directly: the component in the direction of observation. In the case of so-called spectroscopic binary stars, it can be demonstrated solely on the basis of the periodic shift of spectral lines that one object orbits a second there.
Spectral shifts are particularly important for cosmology . In the standard model of an expanding universe, the light of a distant galaxy is shifted more strongly in the direction of longer wavelengths within the framework of the so-called cosmological redshift , the further away the galaxy in question is from us. Measurements of the redshifts in combination with distance measurements are therefore indispensable in order to retrace the evolution of the universe. They could be used, for example, to demonstrate the acceleration of cosmic expansion, an indication of a new form of energy known as dark energy . On the other hand, the redshift is a direct measure for the distance of distant galaxies and active galaxy nuclei , the distance of which cannot be determined in any other way. Corresponding "Redshift Surveys", systematic surveys of galaxies with evaluation of the redshifts, provide important information on the evolution of galaxies.
Investigations at different wavelengths
For most of its history, astronomy was limited to observing the celestial bodies in the realm of visible light . Modern astronomy, on the other hand, uses observations from large parts of the electromagnetic spectrum that complement each other. Astronomical observation methods that use multiple wavelength ranges of the electromagnetic spectrum are known as multi-wavelength astronomy .
The radio astronomy observed in the wavelength range between millimeters and hundreds of kilometers. The majority of astronomical objects radiate only weakly in this area; Even the most distant strong radio sources are all the more clearly visible, especially since radio waves are hardly absorbed by interstellar clouds of dust and fog . In this way, distant radio galaxies , but also dwarf galaxies behind the galactic disk, can be easily observed. Most pulsars - rotating neutron stars from which extremely regular, pulse-like signals can be picked up on Earth - can also be observed in the radio range. The most important observations of cosmic background radiation , which arose around 14 billion years ago, also fall into the microwave range . It provides information about the conditions in the early, hot universe, a mere 400,000 years after the Big Bang .
The microwave range is also used by radar astronomy , the techniques of which, however, can only be applied to our cosmic neighborhood in the solar system: With the help of a radio telescope , high-intensity microwaves are sent in the direction of an astronomical object and the reflected signal is intercepted. For example, the surfaces of planets , but also of asteroids and some comets can be measured.
The infrared astronomy , with wavelengths between 700 nm and 300 microns , is suitable for a comparatively Monitoring cold objects such as brown dwarfs and such stars, the deep inside of molecular clouds are embedded. In addition, the interstellar dust is far more transparent at such wavelengths than for visible light; areas that are otherwise hidden behind dust become visible, such as the nuclei of infrared galaxies , protostars that are just beginning to form, and the center of our own galaxy , including the immediate vicinity of the supermassive black hole it contains .
The infrared radiation is followed by visible light, the observation area of the visual astronomy already mentioned above . Beyond this is the range of ultraviolet astronomy , with wavelengths between 10 and 380 nm. This is where very hot stars can be observed particularly well. In addition, there are a particularly large number of spectral lines in this wavelength range. UV observations provide important information about all phenomena in which spectral lines - or their shift - play a role, for example about binary stars or the flows of matter in the vicinity of stars. On the other hand, this wavelength range is favorable in order to use absorption lines to determine the properties of the interstellar medium that is located in the space between the observer and the distant object being observed.
X-rays and gamma rays
The X-ray astronomy in the wavelength range between 12 nm and about 2.5 pm is dedicated to, the following relationship between the temperature of an object and from it mainly emitted radiation, primarily very hot objects. These include the accretion disks of black holes and X-ray binary stars . Other typical astronomical X-ray sources are hot gas that collects in the centers of galaxy clusters , shock fronts in the atmosphere of young stars or the corona of older stars like our sun.
The gamma-ray astronomy finally comprises radiation having wavelengths in the picometer range and below by. The objects of observation are shock fronts and the vicinity of black holes, i.e. active galaxy nuclei and microquasars . In addition, so-called gamma - ray bursts are investigated: short, extremely high- energy events, the source of which is assumed to be certain types of supernova explosions or the merging of neutron stars , depending on their duration .
In addition to electromagnetic radiation , certain types of particle radiation that originate from space can be detected on earth. They are the object of investigation in observational astroparticle physics .
The so-called primary cosmic radiation consists mainly of protons , electrons and isolated heavier (and completely ionized ) atomic nuclei . Part of this is the so-called solar wind . Secondary cosmic rays arise when these particles collide with the atoms of the earth's atmosphere. Candidates for sources of galactic and extragalactic cosmic rays are the shock fronts of supernova explosions and focused jets that arise in the immediate vicinity of black holes and other compact objects.
Another type of cosmic particle flow that can be detected on earth are cosmic neutrinos , which are generated, for example, during supernova explosions. So far, neutrinos from the sun and from the supernova 1987A have been detected. The - as yet unreached - goal of larger detectors is also to be able to detect neutrinos from nearby active galactic nuclei . Another goal of astroparticle physics is research into so-called dark matter , which so far can only be detected indirectly through its gravitational effect. It is believed that this matter consists of a previously unknown species of elementary particles; Particle detectors such as CRESST or EDELWEISS are supposed to detect these particles. Even the highest-energy electromagnetic gamma radiation, which cannot be detected with telescopes but only with particle detectors , is assigned to astroparticle physics.
Gravitational wave astronomy
Gravitational wave astronomy is still unrealized . Here the information carriers are not electromagnetic waves or elementary particles, but rather distortions of space-time itself, which propagate at the speed of light . The existence of these waves is predicted by general relativity ; They were indirectly detected by conventional astronomical observations on binary star systems such as PSR 1913 + 16 . Gravitational wave detectors such as VIRGO , GEO600 and the LIGO detectors work on direct detection . The aim is to obtain information about cosmic events such as the merging of neutron stars and black holes , asymmetrical supernova explosions or phase transitions in the early universe by measuring the associated gravitational waves .
Instruments and methods
Some of the oldest astronomical instruments are used to use the movement of the celestial bodies to determine the time. The best-known example are the sundials , which make use of the path of the sun. But also for more general instruments like astrolabes the time determination from the position of certain stars was an important application.
On the other hand, a time measurement that is independent of the sky movement is essential for exact position measurements. The first astronomical applications date back to the 14th century, and the development of mechanical clocks was closely linked to astronomy. In addition to the scientific clocks, there were representative versions of astronomical clocks that directly reproduced the movement of the sun, moon and planets.
From the development of precise chronometers (for determining geographical longitude ) to the first public time service (of the Harvard College Observatory from December 1851), the joint development of time measurement and astronomy continued. The basis of time measurement in modern observational astronomy is the international atomic time TAI, which is accessible worldwide via the satellite navigation system GPS with comparatively little effort and high accuracy. Exact time marks are used in astrometry, but also, for example, when interconnecting radio telescopes that are far away ( Very Long Baseline Interferometry ), when determining laser distances, when measuring radar and when detecting tiny irregularities in the otherwise extremely regular signals received from pulsars .
Since their first documented use by Galileo Galilei , telescopes have been the central observation instruments in astronomy. In an optical telescope, suitable arrangements of lenses and / or mirrors collect light from a much larger collecting area than that of the human eye. The collected light is combined to form an image of the object, which also has a higher angular resolution compared to the eye.
The core of every telescope is the optics. In professional astronomy, the pure lens telescopes (refractors) have largely been replaced by reflector telescopes , which can be constructed much larger (and therefore more powerful). In the case of Schmidt cameras or similar telescopes, special correction lenses are used in front of the mirror arrangement. The largest telescopes currently being planned are the Thirty Meter Telescope (30 meters in diameter) and the E-ELT , the “European Extremely Large Telescope”, whose diameter will be 39 m.
Amateur astronomers use smaller instruments of about 10 to 30 cm, often in designs that are cheaper to manufacture than those of the professionally used telescopes. Examples are the Newton telescope - especially in the very simple Dobsonian mount - and the Schmidt-Cassegrain telescope .
For reasons of stability, professional telescopes are stored separately from the surrounding building on their own foundation. Protective domes keep out the weather and prevent telescopes from heating up due to solar radiation and changing their shape due to thermal expansion or wind pressure.
For almost all scientific observations it is necessary to compensate for the rotation of the earth by slowly rotating the telescope in the opposite direction. For a long time, equatorial mounts were common, in which the telescope is aligned in such a way that the rotation of the earth is compensated for by rotating around a single mechanical axis. In contrast, non-parallactic mounts (especially the altazimuthal mount ) offer the advantage of higher mechanical stability, so that they are used more and more in modern large telescopes. However, in addition to tracking the telescope, they also require a relative rotation of the camera and telescope; otherwise the same section of sky would always be observed, but the orientation of the sky region depicted would rotate relative to the camera over time. Modern telescopes are all controlled by computers.
A number of specialized instruments are in use for observing the sun , where the requirements are not low but, on the contrary, very high brightness. Often, solar telescopes are attached in a fixed orientation; the mirrors of a so-called coelostat , which track the sun, reflect the sunlight into the telescope. The interior of solar telescopes is usually evacuated because the air that heats up would distort the image. In coronographs , the solar disk is artificially covered in order to be able to examine the solar corona.
Astrophotography and electronic imaging
Before photography was invented , all astronomy depended on the eye alone. As soon as the film material became light-sensitive enough, photographic methods prevailed throughout astronomy: the human eye only evaluates the impressions of fractions of a second, while a photograph collects light as long as the shutter is open. The resulting image is recorded for a long time so that many astronomers can use and evaluate the same data. The astrophotography uses special photographic films or glass plates with a photographic emulsion is coated. Certain types of telescope, such as the Schmidt camera, are designed from the outset for use in conjunction with a camera and do not allow observation with the naked eye.
Special instruments were used to evaluate photo plates. One example are devices that were used to precisely measure the object positions; Another example are blinking comparators or stereo comparators , which made it possible to compare two images and were used to search for objects such as asteroids or comets whose position changes rapidly relative to the fixed star sky.
The photo played a crucial role in observational astronomy for over a century. Today, the knowledge of photographic methods is almost only useful for professional astronomers in order to be able to assess the properties of the data from previous surveys that are available in the form of photo plates: In the last 30 years, photos have been almost completely used as recording media by digital sensors such as CCDs (also used in digital cameras) and CMOS chips, which are significantly more sensitive to light than film, are being replaced. Special areas such as photometry and interferometry have been using electronic detectors such as photomultipliers for a considerably longer period of time.
Electronic observations have the advantage that the relevant raw images are accessible directly after the observation without a development process . The image data can also be processed further directly in the computer. Measurements with electronic detectors follow a characteristic sequence: In the simplest case, a test recording in complete darkness (e.g. with a covered telescope) is used to determine which signal the detector delivers when no light falls on it. Then, by observing an evenly illuminated white area, it is determined to what extent some detector regions are more sensitive than others. The data from both test recordings will be used later to correct the astronomical recordings accordingly.
Dealing with the effects of the earth's atmosphere
Optical and radio astronomy can be carried out from the ground, since the atmosphere is relatively transparent to light of the wavelengths concerned . Observatories are often located at high altitudes to minimize absorption and distortion from the Earth's atmosphere, as well as cloud degradation. Some wavelengths of infrared light are strongly absorbed by water vapor. Some mountain peaks have a high number of cloud-free days and generally have good atmospheric conditions (i.e. good visibility conditions). The tips of the islands of Hawaii and La Palma have these characteristics, and certain inland locations also offer suitable conditions, for example Paranal , Cerro Tololo and La Silla in Chile .
Observations from the ground are affected by a number of disruptive effects. Air movements in the atmosphere cause the images of astronomical objects to shift and distort over short time scales. The so-called seeing (the blurring of the image due to air turbulence ) often limits the theoretical resolution of the telescope considerably under the given conditions . It can be noticeable in the visible part of the spectrum at openings of 15–20 centimeters and makes larger telescopes i. d. Most of the blurring is usually done. However, a number of methods such as adaptive optics , speckle interferometry and lucky imaging make it possible to at least partially compensate for the atmospheric effects.
The darkness of the night is an important factor in observational astronomy. Due to the increasing size and population density of cities, the amount of artificial light also increases at night. Artificial light sources create a diffuse background lighting that makes it difficult to observe weakly luminous objects. In some places, such as in the US state of Arizona or in Great Britain , official measures to reduce such light pollution have already been taken. The use of suitable lampshades on street lamps, for example, not only reduces the amount of light emitted into the sky, but also ensures better lighting on the ground. Part of the light pollution can be compensated for by filters during astronomical observations . If a filter only lets through that light in which the targeted object shines particularly brightly ( e.g. fog filter for individual spectral lines), a large part of the scattered light is blocked out.
Even beyond the questions of resolution and light pollution, the influence of the atmosphere must be taken into account when taking measurements on earth. On the one hand, the light from a distant celestial object is partially absorbed in the atmosphere, and the more so, the lower the object, as seen by the observer, is above the horizon (so-called extinction ). This has to be taken into account when it comes to measuring the brightness of an object either directly or comparing it with that of another object. On the other hand, the incident light is refracted in the earth's atmosphere ; this affects the apparent position of an object in the sky (so-called astronomical refraction ). This effect also depends on how high the object is above the horizon.
To avoid the disturbing effects of the atmosphere for observations in visible light as well as for observations of X-ray, gamma-ray, UV and (with small exceptions, so-called wavelength windows) infrared light, it makes sense to overcome the atmosphere. One possibility are balloon telescopes such as BOOMERanG or telescopes in high-flying aircraft such as the Lear Jet Observatory , the Kuiper Airborne Observatory or SOFIA . It goes even higher with space telescopes such as the Hubble Space Telescope , its planned successor, the James Webb Space Telescope , X-ray satellites such as ROSAT or the WMAP microwave telescope . Radio astronomers also try to avoid earthly sources of interference, which threaten to overlay the weak radio signals from astronomical objects. A number of radio astronomy satellites are in use; A radio telescope on the far side of the moon is also being considered.
For photometry, the measurement of the brightness of a given object, comparison methods are mostly used nowadays. Instead of measuring the radiation flux of the object in question directly, it is compared with the radiation flux of a nearby reference object whose brightness is known from systematic measurements.
Modern photometric measurements use a property of the CCD detectors that are used for astronomical image acquisition: over a wide brightness range, the brightness of the image of an object electronically captured by the CCD is proportional to its ( apparent ) brightness. It is important to take into account not only the characteristic properties of the detector, but also the extinction . This can be done by measuring the brightness of the observation object at different heights above the horizon; this data allows one to extrapolate how bright the object would be without the influence of the earth's atmosphere.
In connection with filters , brightness measurements also represent a preliminary stage of spectrometry. Filters only allow radiation from a limited part of the spectrum of an object through; Brightness measurements with upstream filters therefore give a rough overview of the spectrum of a star, for example. A suitably selected system of standard filters, such as the widely used UBV system , makes it possible to determine the spectral type of a star and the temperature of its outer layers.
In combination with a telescope, the spectroscope is a standard astronomical instrument. Early spectroscopes split light into its various wavelengths with the help of prisms ; Before the introduction of astrophotography, such a prism was built directly into the telescope's eyepiece .
Modern spectroscopes are designed as spectrographs : the spectrum is recorded on film or by detectors. With spectrographs, the light of one and the same astronomical object can be recorded with long exposure; in this way, the spectra of weak objects can also be determined, such as distant galaxies. The resolution - the smallest distance between two spectral lines that can still be distinguished from each other - results from the resolution and the focal length of the camera, the maximum exposure time and the resolution of the element used to split the light. The latter is almost always an optical diffraction grating in modern instruments . On the one hand, the use of gratings reduces the loss of light compared to prisms. In addition, gratings can be shaped in such a way that a certain diffraction order appears particularly bright; In this way, a particularly high resolution of the spectrum can be achieved with low orders. To put it simply, different spectral images of one and the same object result from the decomposition of light; With these special gratings, one of them is particularly bright. The so-called Echelle spectrographs are particularly effective , in which the higher orders of a conventional diffraction grating fall on a second grating, the Echelle grating, which is arranged perpendicular to the first grating and separates the higher orders from one another .
Wavelengths beyond visible light
The basic principle of telescopes for other wavelengths is the same as for visible light: an optical system collects the incoming radiation and directs it to a detector. The type of detector in particular is characteristic of the radiation area being examined.
For ultraviolet telescopes, the optics do not differ noticeably from those for use with visible light; however, certain wavelengths require the use of specially coated mirrors. The same applies to infrared astronomy; there the main difference lies in the cooling of all telescope components, which is necessary to eliminate disruptive heat radiation .
Radio telescopes, on the other hand, have a noticeably different appearance than their optical counterparts. The smallest achievable resolution generally results from the ratio of the wavelength of the captured radiation and the diameter of the area with which the radiation is collected. Because of the long wavelengths of the radio waves, very large “dishes” are therefore necessary in order to generate “radio images” with a sufficiently good resolution. Thanks to technical advances, radio telescopes now achieve resolutions of less than a thousandth of an arc second.
X-ray telescopes - due to the impermeability of the atmosphere to X-rays only in the form of satellite telescopes such as ROSAT or Chandra - have a characteristic structure, which is due to the fact that X-ray light cannot be reflected with conventional mirrors. Up to an upper energy limit of around 10 keV , so-called Wolter telescopes are used, at whose nested mirrors flatly incident X-rays are reflected. In the case of energies above this, the “optics” consist of collimators , which only allow X-ray radiation to pass through from a very specific direction, or of “coded masks” whose shadows cast the direction of the incident X-ray light. CCDs, other semiconductor detectors and scintillation counters , for example, can be used as detectors .
Rough directional determinations are possible wherever two reference objects can be used. With the Neolithic stone circle of Stonehenge , it was already possible to record the position of the sun at the time of the solstice and then to infer the return of this time with the help of the suitably positioned stones.
More precise direction finding devices such as Jacob's staff , simple quadrants or armillary spheres already made quantitative measurements possible with the naked eye, before the combination of telescope and direction finding device led to the development of more precise measuring instruments, from hand-held sextants for navigation to astronomical theodolites . An important instrument are meridian circles or passage instruments that can only be swiveled in one plane (from the south point to the zenith to the north point); it is measured when and at what altitude a planet or star passes the direction of observation ( star passage ). Star occultations by the moon, asteroids or planets - more rarely also mutual star occultations - give the opportunity to determine the relative positions of the celestial bodies involved with great accuracy.
Before the introduction of photographic methods, special measuring devices were used to determine the angular distance between objects - such as double stars - that are visible together in the field of view of a telescope. An example is a split lens micrometer. By shifting the lens parts against each other, the images of two different star disks can be brought into agreement; the extent of the necessary shift is a measure of the angular spacing of the stars.
With the advent of photographic methods, techniques became possible in which the relative distances of different objects are determined directly on the photographic plate or from the electronic image data. However, the angles that can be measured in this way are comparatively small; if a network of celestial positions is reconstructed from such small angles, the total error is comparatively large. With astrometry satellites like Hipparcos and Gaia , the light of two telescopes attached at a fixed angle to one another is directed onto the same detector; the accuracy of the base angle is precisely monitored with the help of a laser system. A large number of larger angles are measured and connected to a network of star positions.
In interferometry , the observations of several telescopes are combined in such a way that the result corresponds to the resolution of a much larger telescope. This technique was first applied to radio telescopes. The currently largest radio observatory with 27 coupled telescopes is the Very Large Array in the US state of New Mexico . As part of the so-called Very Long Baseline Interferometry , radio telescopes are "interconnected" at distant locations, the observation data of which are provided with highly precise time markings, recorded and subsequently combined with one another in the computer. With the inclusion of satellite telescopes, measurements are possible for which a single telescope would have to be far larger than the earth.
Interferometry also plays a role in the visible range, although the process is technically very difficult to implement due to the disparately smaller wavelengths (micrometers instead of decimeters). Early devices such as the Michelson star interferometer guided the starlight into the same telescope in two different ways with the help of an arrangement of mirrors. Modern optical interferometers combine the light from different telescopes. Examples are the Large Binocular Telescope Interferometer, which is currently being set up, with two interconnected reflecting telescopes on Mount Graham in Arizona and the Very Large Telescope Interferometer at the Paranal Observatory of the European Southern Observatory , in which two or three telescopes (combinations of four 8.2 -m- or four 1.8-m telescopes) can be connected together.
The high-energy cosmic rays , but also high-energy gamma rays, when they hit atoms in the earth's atmosphere, generate showers of particles (secondary cosmic rays). In observatories such as the Pierre Auger Observatory , the shower particles are detected in water tanks; the Cherenkov radiation generated when the fastest particles pass through the water can be measured directly.
Cosmic neutrinos are also detected in this way in huge water tanks such as that of the Super Kamiokande detector in Japan. More recent experiments make use of natural water resources, such as AMANDA or IceCube , in which radiation detectors are inserted directly into the Antarctic ice .
In gamma astronomy, on the other hand, an important observation method is to observe the Cherenkov light flashes that are generated when the gamma rays pass through the atmosphere. This is, for example, the observation goal of the telescopes of the HESS project. Outside the earth's atmosphere, gamma rays can be detected directly: satellites such as GLAST carry scintillation counters in which detectable flashes of light are generated when gamma radiation hits with photomultipliers or semiconductor detectors .
Gravitational wave detectors
Two types of detectors are currently in operation to directly detect gravitational waves for the first time. Interferometric detectors measure how the frequency of a highly stable laser beam changes, which is reflected between mirrors suspended in an isolated manner and is minimally stretched or compressed by continuous gravitational waves. This is the functional principle of the LIGO detectors from Virgo and the German-British detector GEO 600 . Resonance detectors, on the other hand, take advantage of the fact that a continuous gravitational wave of a suitable frequency should set a solid - such as a solid metal cylinder or a metal ball - into tiny vibrations that can just be detected with suitable sensors.
- SD Birney et al .: Observational astronomy. Cambridge Univ. Press: Cambridge 2006, ISBN 0-521-85370-2 .
- WA Cooper et al .: Observing the universe - a guide to observational astronomy and planetary science. Open University: Milton Keynes 2004, ISBN 0-521-60393-5 .
- Michael Hoskin (ed.): The Illustrated Cambridge History of Astronomy. Cambridge Univ. Press: Cambridge 1997, ISBN 0-521-41158-0 .
- CR Kitchin: Astrophysical Techniques . CRC Press, Boca Raton 2009, ISBN 978-1-4200-8243-2 .
- Ian S. McLean: Electronic imaging in astronomy - detectors and instrumentation. Springer, Berlin 2008, ISBN 978-3-540-76582-0
- JB Sidgwick: Amateur Astronomer's Handbook . 4th edition. Enslow Publishers: Hillside 1980, ISBN 0-89490-049-8 .
- Alfred Weigert and Heinrich Johannes Wendker : Astronomy and Astrophysics - a basic course . 2nd Edition. VCH publishing company: Weinheim 1989, ISBN 3-527-26916-9 .
- On the beginnings of the exploration of the moon and planets by American probes, see Harro Zimmer: 50 Years of NASA . In: Sterne und Weltraum Vol. 10/2008, pp. 46–59. For the Soviet space probes, see ders .: Russia's way to the planets . In: Sterne und Weltraum Vol. 5/2008, pp. 50–63. Peter Janle provides an overview of the knowledge gained in this way: The image of the planetary system through the ages. Part 2: From the 19th century to today . In: Stars and Space, Vol. 4/2006, pp. 22–33.
- Section 2.7 in Wolfram Winnenburg: Introduction to Astronomy. BI Wissenschaftsverlag: Mannheim u. A. 1990, ISBN 3-411-14441-6 . For the systematic search for meteorites Thorsten Dambeck: Black stones in polar ice . In: Astronomie Heute 9–10 / 2003, pp. 62–64.
- An example of this kind of conclusion is the history of systematic constellations such as the Hertzsprung-Russel diagram, see Werner Pfau: Streifzüge durch das Hertzsprung-Russel diagram. Part 1: From observation to the theory of the stars. In: Stars and Space Vol. 6/2006, pp. 32–40. On the cosmological principle, for example, Section 14.1. in Steven Weinberg: Gravitation and Cosmology . John Wiley, New York 1972, ISBN 0-471-92567-5 .
- z. B. Section 1.2 in H. Karttunen, P. Kröger, H. Oja, M. Poutanen and KJ Donner (eds.): Astronomie. An introduction . Springer, Berlin et al. 1987, ISBN 3-540-52339-1 .
- See James Cornell: The First Astronomers. Birkhäuser: Basel et al. 1983.
- Part 3 (Greeks), 12 (Arabs) and p. 464ff. (Brahe) in E. Zinner: The history of astronomy. Springer: Berlin 1931.
- See p. 64f. in Hoskin 1997.
- Galilei p. 122f., Mirror telescope p. 152f., Herschel's Telescope p. 233ff., Parsons p. 253ff. in Hoskin 1997.
- JB Hearnshaw: The analysis of starlight. One hundred and fifty years of astronomical spectroscopy. Cambridge Univ. Press: Cambridge et al. 1986, ISBN 0-521-25548-1 .
- p. 288f. in Hoskins 1997.
- Radioastronomie p. 482f., Photomultiplier p. 400f., Electronic image acquisition p. 391 in John Lankford (ed.): History of Astronomy. To Encyclopedia. Garland Publishing: New York and London 1997, ISBN 0-8153-0322-X .
- V2 rocket and UV: p. 533, IRAS p. 268, Uhuru p. 570, Luna probes p. 335, in John Lankford (ed.): History of Astronomy. To Encyclopedia. Garland Publishing: New York and London 1997, ISBN 0-8153-0322-X .
- Hess and Successor p. 7ff., Neutrinos p. 210f. in MS Longair: High energy astrophysics. Volume 1. Cambridge University Press: Cambridge et al. 1992, ISBN 0-521-38374-9 .
- Hubble telescope: Tilmann Althaus: 15 years of Hubble . In: Stars and Space Vol. 7/2005, pp. 22–33. Active and adaptive optics: Section 1.1.21 in Kitchin. Gravitational wave detection: Peter Aufmuth: On the threshold of gravitational wave astronomy . In: Stars and Space Vol. 1/2007, pp. 26–32.
- Heino Falcke and Rainer Beck: Via software to the stars . In: Spektrum der Wissenschaft 7/2008, pp. 26–34.
- On the historical background, Chapter 2 in Arnold Hanslmeier : Introduction to Astronomy and Astrophysics. Spectrum Academic Publishing House: Berlin and Heidelberg 2007, ISBN 978-3-8274-1846-3 . On the zodiac Hans Georg Gundel: Zodiacos: Zodiac images in antiquity. Cosmic references and ideas of the afterlife in everyday life in ancient times (cultural history of the ancient world, vol. 54). Philipp von Zabern, Mainz am Rhein 1992, ISBN 3-8053-1324-1 . The modern constellations are presented on the IAU website: The Constellations (last accessed October 6, 2008).
- On comets, chap. 1 in John C. Brandt and Robert D. Chapman: Introduction to Comets. Cambridge University Press: Cambridge 2004, ISBN 0-521-80863-4 . Using the example of the supernova of 1006, for example, Christian Pinter: A guest a thousand years ago . In: Astronomie Heute Vol. 5/2006, pp. 48–49. On comets on coins Wilhelm J. Altenhoff: Comets on old coins . In: Stars and Space, Vol. 5/2006, pp. 34–37.
- On early astronomy with telescopes: Harald Siebert: The beginnings of stellar astronomy. In: Stars and Space Vol. 7/2006, pp. 40–49.
- For Messier Catalog see Owen Gingerich: Messier and His Catalog I . In: Sky & Telescope , Vol. 12, August 1953, pp. 255-258 and 265, bibcode : 1953S & T .... 12..255G ; ders .: Messier and His Catalog II . In: Sky & Telescope , Vol. 12, September 1953, pp. 288-291. bibcode : 1953S & T .... 12..288G ; On NGC / IC (and a project to create a corrected version of it) Steve Gottlieb: Cleaning up in space . In: Astronomie Heute Vol. 1–2 / 2004, pp. 52–54.
- E.g. Weigert / Wendker, Section 1.1.
- An overview is provided by Jean Kovalevsky and P. Kenneth Seidelmann: Fundamentals of astrometry . Cambridge University Press, Cambridge 2004, ISBN 0-521-64216-7 .
- To the Ludwig Rohner calendar : Calendar history and calendar. Akad. Verl.-Ges. Athenaion, Wiesbaden 1978, ISBN 3-7997-0692-5 ; for the second section 3.3. in Sigmar German and Peter Drath: Handbuch SI-Einheit . Vieweg: Braunschweig and Wiesbaden 1979, ISBN 3-528-08441-3 .
- Wolf Nebe: Practice of Astronavigation. Delius Klasing, Bielefeld 1997, ISBN 3-7688-0984-6 .
- On Brahe see, for example, Volker Witt: Tycho Brahe - Wegbereiter der Himmelsmechanik . In: Stars and Space Vol. 11/2001, pp. 994-996.
- On parallax Alan W. Hirshfeld: The race to measure the universe . In: Astronomie Heute Vol. 10/2004, pp. 22-27.
- Stephen Koszudowski: Journey of Discovery to the Planets . In: Astronomie Heute Vol. 7–8 / 2006, pp. 16–23.
- Pais, Abraham: "Subtle is the Lord ..." The Science and life of Albert Einstein , pp. 253-254. Oxford University Press, Oxford 1982, ISBN 0-19-853907-X .
- On Hipparcos Ulrich Bastian: The measured starry sky - results of the Hipparcos mission . In: Spektrum der Wissenschaft Vol. 2/2000, S. 42ff .; also the Hipparcos Science Pages of ESA (last accessed October 4, 2008). To Gaia Thorsten Dambeck: The mapping of the Milky Way . In: Astronomie Heute Vol. 5/2006, pp. 14-18.
- Absolute and apparent brightness, e.g. B. in Weigert / Wendker, Sections 3.2 and 4.1.2. For the Cepheids, see Gerhard Mühlbauer: Cepheids - Milestones in the Universe . In: Stars and Space, Vol. 10/2003, pp. 48–49. For type Ia supernovae see Bruno Leibundgut: Bright stars in the dark universe . In: Stars and Space Vol. 5/2005, pp. 30–37.
- NAAP Astronomy Labs - Eclipsing Binary Stars - Eclipsing Binary Simulator , Cornell Astronomy. See also D. Gossman, Light Curves and Their Secrets , Sky & Telescope (October 1989, p.410).
- E.g. Weigert / Wendker, Section 4.3 and Chapter 5.
- Section 7.8 in Werner Israel: Dark Stars: The Evolution of an Idea . In: S. Hawking and W. Israel (eds.): 300 Years of Gravitation , pp. 199-276. Cambridge University Press, Cambridge 1987.
- E.g. Chapter 5 in Marc L. Kutner: Astronomy: A Physical Perspective. Cambridge University Press: Cambridge et al. 2003, ISBN 0-521-82196-7 . General Wulff-Dieter Heintz: Double stars . Goldmann, Munich 1971, ISBN 3-442-55012-2 .
- E.g. Weigert / Wendker, Section 6.2 and Chapter 14 in BW Carroll and Dale A. Ostlie: An Introduction to Modern Astrophysics . Pearson / Addison-Wesley: San Francisco et al. 2007, ISBN 0-321-44284-9 . Specifically on the Cepheids, the article by Gerhard Mühlbauer already quoted: Cepheids - Milestones in the Universe . In: Stars and Space, Vol. 10/2003, pp. 48–49.
- On the historical background z. B. Alan W. Hirshfeld: Detectives of the Starlight . In: Astronomie Heute Vol. 12/2004, pp. 22–28. On spectroscopy in general Keith Robinson: Spectroscopy: The Key to the Stars. Reading the Lines in Stellar Spectra . Springer: London 2007, ISBN 0-387-36786-1 .
- To the spectral classes z. B. Weigert / Wendker Section 4.3. To the Hertzsprung-Russel diagram: Werner Pfau: Forays through the Hertzsprung-Russel diagram. Part 1: From observation to the theory of the stars. In: Stars and Space Vol. 6/2006, pp. 32–40.
- E.g. Weigert / Wendker p. 83f.
- Harry Nussbaumer: Eighty Years of Expanding Universe . In: Stars and Space Vol. 6/2007, pp. 36–44.
- A list can be found in the category: screening . Information on more recent surveys is available, for example, on the Sloan Digital Sky Survey and the 2 Micron All Sky Survey websites .
- The difference between information in the entire spectrum and information over narrow spectral ranges can be made audible by the analogy between light and sound frequencies. This is impressively demonstrated in David Helfand's presentation Seeing the Whole Symphony (CCNMTL, Columbia University).
- Bernard F. Burke and Francis Graham-Smith: An Introduction to Radio Astronomy. Cambridge University Press, Cambridge 1996, ISBN 0-521-00517-5 .
- E.g. Kitchin, Section 2.8.
- The articles in A. Mampaso, M. Prieto and F. Sanchez (eds.): Infrared Astronomy provide an overview . Cambridge University Press: Cambridge 2004, ISBN 0-521-54810-1 . The development of this branch of astronomy is described by Frank J. Low, GH Rieke, RD Gehrz: The Beginning of Modern Infrared Astronomy. In: Annual Review of Astronomy and Astrophysics. 45, 2007, pp. 43-75, doi: 10.1146 / annurev.astro.44.051905.092505 .
- Basics z. B. in RC Bless and AD Cod: Ultraviolet Astronomy . In: Annual Review of Astronomy and Astrophysics Vol. 10 (1972), pp. 197-226, doi: 10.1146 / annurev.aa.10.090172.001213 . More modern developments and future observation goals in: Ana I. Gómez de Castro and Willem Wamsteker (eds.): Fundamental Questions in Astrophysics: Guidelines for Future UV Observations . Springer: Dordrecht 2006, ISBN 1-4020-4838-6 .
- The articles in Joachim Trümper and Günther Hasinger (eds.): The Universe in X-Rays provide an overview . Springer: Berlin and others, ISBN 978-3-540-34411-7 .
- Christopher Wanjek: Gamma Astronomy . In: Astronomie Heute Vol. 3/2004, pp. 30–36.
- See Christian Spiering: Astroparticle Physics . In: Sterne und Weltraum Vol. 6/2008, pp. 46–54; The brochure Cosmic Searching for Traces by the Committee for Astroparticle Physics also provides an overview .
- Christian Stegmann: Cosmic radiation: The search for the sources . In: Stars and Space Vol. 3/2006, pp. 24–34.
- See e.g. B. Kitchin, Section 1.7.
- Peter Aufmuth: On the threshold to gravitational wave astronomy . In: Stars and Space Vol. 1/2007, pp. 26–32.
- P. 46–167 in Ernst Zinner: German and Dutch astronomical instruments of the 11th-18th centuries . Century. CH Beck: Munich 1972, ISBN 3-406-03301-6 .
- Section “Scientific Clocks”, p. 29f. in Ernst Zinner: German and Dutch astronomical instruments of the 11th-18th centuries Century. CH Beck: Munich 1972, ISBN 3-406-03301-6 and pp. 83 and 138 in Hoskin 1997.
- W. Andrewes: Time and Timekeeping in John Lankford (ed.): History of Astronomy. To Encyclopedia. Garland Publishing: New York and London 1997, ISBN 0-8153-0322-X .
- Section 2.4. in Jean Kovalevsky and P. Kenneth Seidelman: Fundamentals of Astrometry. Cambridge University Press: Cambridge et al. 2004, ISBN 0-521-64216-7 .
- E.g. Heinz Niederig (ed.): Bergmann / Schaefer textbook of experimental physics. Vol. 3: Optik , pp. 172-179. Walter de Gruyter: Berlin and New York 1993, ISBN 3-11-012973-6 .
- Dietrich Lemke: The future is bright - but expensive . In: Stars and Space, Vol. 10/2008, pp. 28–35. For information about the E-ELT, see the Future Facilities: E-ELT website on the European Southern Observatory's web portal (last accessed on August 31, 2019).
- J. Biefang: The telescope: Your view into space . In: Astronomy for All. Stars and Space Basics 1, pp. 22–31. Stars and space publishing house, spectrum of science publishing company, Heidelberg, ISBN 3-936278-24-5 .
- Kitchin, Section 1.1.23.
- Kitchin, Section 1.1.20.
- E.g. chap. 3 in Michael Stix: The Sun. An Introduction. Springer: Berlin et al. 2002, ISBN 3-540-42886-0 .
- E.g. Kitchin, Section 2.2 .; on Schmidt cameras pp. 100-101.
- Flashing comparator: Sidgwick, Section 22.8.
- Kitchin, Section 2.2.
- See e.g. B. Kitchin, Sections 1.1 and 2.3.
- See Chapters 12 and 16 in W. Romanishin, An Introduction to Astronomical Photometry Using CCDs (PDF; 2 MB).
- On the classic observatory locations Siegfried Marx and Werner Pfau: Sternwarten der Welt . Herder: Freiburg et al. 1980, ISBN 3-451-18903-8 .
- For the interference effects, see Chapter 2 (especially on speckle interferometry, Section 2.3.3 and on adaptive optics, Section 2.4) in Ian McLean: Electronic Imaging in Astronomy: Detectors and Instrumentation . Springer: Berlin et al. 2008, ISBN 978-3-540-76582-0 . For Lucky Imaging, see NM Law, CD Mackay and JE Baldwin: Lucky imaging: high angular resolution imaging in the visible from the ground. In: Astronomy and Astrophysics Vol. 446, Vol. 2 (2006), pp. 739-745. bibcode : 2005astro.ph..7299L
- Bob Mizon: Light Pollution: Responses and Remedies. Springer: London 2002, ISBN 978-1-85233-497-0 . Information with a focus on Germany on the website of the Initiative against Light Pollution (last accessed on November 1, 2008).
- E.g. Chapter 8 in Michael E. Bakich: The Cambridge Encyclopedia of Amateur Astronomy . Cambridge University Press: Cambridge 2003. ISBN 978-0-521-81298-6 .
- Section 2.3. in J. Krautter, E. Sedlmayr, K. Schaifers and G. Traving: Meyers Handbuch Weltall . Meyers Lexikonverlag: Mannheim u. A. 1994, ISBN 3-411-07757-3 .
- On Boomerang see Michael Burton: Astronomy at the end of the world . In: Stars and Space Vol. 12/2004, pp. 22-29. On airborne telescopes Cecilia Scorza de Appl: Astronomy at lofty heights . In: Sterne und Weltraum Vol. 7/2008, pp. 64–67.
- On Hubble, for example, Tilmann Althaus: 15 years of Hubble . In: Stars and Space Vol. 7/2005, pp. 22–33. To the James Webb Telescope Dietrich Lemke: Construction of the James Webb Space Telescope on schedule . In: Stars and Space Vol. 10/2007, pp. 21-23.
- Radio astronomy satellite: Hisashi Hirabayashi et al .: The VLBI Space Observatory Program and the Radio Astronomical Satellite HALCA . In: Publ. Of the Astronomical Society of Japan Vol. 52 (2000), pp. 955-965. bibcode : 2000PASJ ... 52..955H ; Radio astronomy on the moon z. BCL Carilli, JN Hewitt and A. Loeb: Low frequency radio astronomy from the moon: cosmic reionization and more . arxiv : astro-ph / 0702070 .
- See Chapter 23 in William Romanishin's script An Introduction to Astronomical Photometry Using CCDs (PDF 1.9 MB; Oakland University, September 16, 2000 version). A widely used catalog of standard stars is Arlo Landolt: UBVRI photometric standard stars in the magnitude range 11.5-16.0 around the celestial equator . In: Astronomical Journal , Vol. 104 (1992), pp. 340-371 and 436-491. bibcode : 1992AJ .... 104..340L
- See Chapters 12, 16 and 17 in W. Romanishin, An Introduction to Astronomical Photometry Using CCDs (PDF; 2 MB).
- HL Johnson and WW Morgan: Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas . In: Astrophysical Journal Vol. 117 (1953), pp. 313-352. bibcode : 1953ApJ ... 117..313J
- E.g. Kitchin, Section 4.2.2.
- E.g. Kitchin, Section 4.2.3. and Section A. Unsöld and B. Baschek: The New Cosmos .
- infrared observations, see IS Glass: Handbook of Infrared Astronomy . Cambridge University Press: Cambridge 1999, ISBN 0-521-63311-7 .
- KI Kellermann and JM Moran: The development of high-resolution imaging in radio astronomy . In: Annual Review of Astronomy and Astrophysics. 39, 2001, pp. 457-509, doi: 10.1146 / annurev.astro.39.1.457 .
- On the Kitchin detectors, Section 1.3.2, and on the Kitchin imaging method, Section 1.3.4.
- C. Ruggles: Astronomy in Prehistoric Britain & Ireland, especially on Stonehenge, pp. 35–41 and 136–139. Yale University Press 1999. For the possibilities of this simplest kind of astronomy, see also Neil DeGrasse Tyson: Death by Black Hole , Chapter 5. Norton: New York and London 2007, ISBN 978-0-393-33016-8 .
- For the development of astronomical instruments, see Dieter B. Herrmann: Vom Schattenstab zum Riesenspiegel: 2000 years of sky research technology . Verlag Neues Leben, Berlin 1988, ISBN 3-355-00786-2 and Ernst Zinner: German and Dutch astronomical instruments of the 11th-18th centuries. Century. CH Beck: Munich 1967, ISBN 3-406-03301-6 .
- See Douglas J. Mink: 100 Years of Occultations: A Statistical View . In: Bulletin of the American Astronomical Society , Vol. 29, 1997, pp. 1023ff. bibcode : 1997DPS .... 29.2703M . The website of the International Lunar Occultation Center ( Memento from October 25, 2008 in the Internet Archive ) provides material on the occultations of the stars by the moon .
- p. 219 in Hoskin 1997.
- On the functional principle of Gaia see Marielle van Veggel et al .: Metrology concept design of the GAIA basic angle monitoring system . In: Proc. SPIE , Vol. 5495, 2004, pp. 11ff.
- On radio interferometry in general: Kitchin, pp. 279–298. For more information on the Very Large Array, see the VLA web portal .
- E.g. Kitchin, Section 2.5.2.
- For the LBT, see K. Jäger, Scientific observations started at the LBT . In: Stars and Space Vol. 7/2007, pp. 16-18. For the VLT interferometer see A. Glindemann: Das VLT interferometer . In: Stars and Space Vol. 3/2003, pp. 24–32.
- See Thomas Bührke: The "Pierre Auger" observatory - New eyes for cosmic rays . In: Stars and Space, Vol. 3/2006, pp. 36–39.
- Current information about the new detectors on the Amanda and IceCube web portals .
- Heinrich J. Völk: New results in gamma astronomy. In: Stars and Space, Vol. 8/2006, pp. 36–45.
- For general on detection methods, see Kitchin, Section 1.3. For GLAST, see Giselher Lichti and Andreas von Kienlin: The GLAST mission . In: Sterne und Weltraum Vol. 5/2008, pp. 40–48.
- Marcia Bartusiak: Einstein's Legacy. The race for the final riddle of the theory of relativity . European Publishing House 2005, ISBN 978-3-434-50529-7 . Markus Pössel: The Einstein Window . Hamburg: Hoffmann & Campe 2005, ISBN 978-3-455-09494-7 .