Gamma-ray astronomy
Gamma-ray astronomy is the astronomical observation of gamma rays, the most energetic form of electromagnetic radiation, with photon energies above 100 keV. Radiation is the subject of X-ray astronomy. In most known cases, gamma rays from solar flares and Earth's atmosphere are generated in the MeV range, but it is now known that gamma rays in the GeV range can be generated by solar flares, it had been believed. As GeV gamma rays are important in the study of extra-solar, extra-galactic, new observations may complicate some prior models and findings."Strange gamma rays from the sun may help decipher its magnetic fields"."NASA's Fermi Sees Gamma Rays from'Hidden' Solar Flares". The mechanisms emitting gamma rays are diverse identical with those emitting X-rays but at higher energies, including electron-positron annihilation, the inverse Compton effect, in some cases the decay of radioactive material in space reflecting extreme events such as supernovae and hypernovae, the behaviour of matter under extreme conditions, as in pulsars and blazars.
The highest photon energies measured to date are in the TeV range, the record being held by the Crab Pulsar in 2004, yielding photons with as much as 80 TeV. Observation of gamma rays first became possible in the 1960s, their observation is much more problematic than that of X-rays or of visible light, because gamma-rays are comparatively rare a "bright" source needing an observation time of several minutes before it is detected, because gamma rays are difficult to focus, resulting in a low resolution. The most recent generation of gamma-ray telescopes have a resolution of the order of 6 arc minutes in the GeV range, compared to 0.5 arc seconds seen in the low energy X-ray range by the Chandra X-ray Observatory, about 1.5 arc minutes in the high energy X-ray range seen by High-Energy Focusing Telescope. Energetic gamma rays, with photon energies over ~30 GeV, can be detected by ground-based experiments; the low photon fluxes at such high energies require detector effective areas that are impractically large for current space-based instruments.
Such high-energy photons produce extensive showers of secondary particles in the atmosphere that can be observed on the ground, both directly by radiation counters and optically via the Cherenkov light which the ultra-relativistic shower particles emit. The Imaging Atmospheric Cherenkov Telescope technique achieves the highest sensitivity. Gamma radiation in the TeV range emanating from the Crab Nebula was first detected in 1989 by the Fred Lawrence Whipple Observatory at Mt. Hopkins, in Arizona in the USA. Modern Cherenkov telescope experiments like H. E. S. S. VERITAS, MAGIC, CANGAROO III can detect the Crab Nebula in a few minutes; the most energetic photons observed from an extragalactic object originate from the blazar, Markarian 501. These measurements were done by the High-Energy-Gamma-Ray Astronomy air Cherenkov telescopes. Gamma-ray astronomy observations are still limited by non-gamma-ray backgrounds at lower energies, and, at higher energy, by the number of photons that can be detected.
Larger area detectors and better background suppression are essential for progress in the field. A discovery in 2012 may allow focusing gamma-ray telescopes. At photon energies greater than 700 keV, the index of refraction starts to increase again. Long before experiments could detect gamma rays emitted by cosmic sources, scientists had known that the universe should be producing them. Work by Eugene Feenberg and Henry Primakoff in 1948, Sachio Hayakawa and I. B. Hutchinson in 1952, Philip Morrison in 1958 had led scientists to believe that a number of different processes which were occurring in the universe would result in gamma-ray emission; these processes included cosmic ray interactions with interstellar gas, supernova explosions, interactions of energetic electrons with magnetic fields. However, it was not until the 1960s that our ability to detect these emissions came to pass. Most gamma rays coming from space are absorbed by the Earth's atmosphere, so gamma-ray astronomy could not develop until it was possible to get detectors above all or most of the atmosphere using balloons and spacecraft.
The first gamma-ray telescope carried into orbit, on the Explorer 11 satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons. They appeared to come from all directions in the Universe, implying some sort of uniform "gamma-ray background"; such a background would be expected from the interaction of cosmic rays with interstellar gas. The first true astrophysical gamma-ray sources were solar flares, which revealed the strong 2.223 MeV line predicted by Morrison. This line results from the formation of deuterium via the union of a proton; these first gamma-ray line observations were from OSO-3, OSO-7, the Solar Maximum Mission, the latter spacecraft launched in 1980. The solar observations inspired theoretical work by others. Significant gamma-ray emission from our galaxy was first detected in 1967 by the detector aboard the OSO-3 satellite, it detected 621 events attributable to cosmic gamma rays. However, the field of gamma-ray astronomy took great leaps forward with the SAS-2 and the COS-B satellites.
These two satellites provided an exciting view into the high-energy universe (sometimes called the'violent' universe
Observational astronomy
Observational astronomy is a division of astronomy, concerned with recording data about the observable universe, in contrast with theoretical astronomy, concerned with calculating the measurable implications of physical models. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments; as a science, the study of astronomy is somewhat hindered in that direct experiments with the properties of the distant universe are not possible. However, this is compensated by the fact that astronomers have a vast number of visible examples of stellar phenomena that can be examined; this allows for observational data to be plotted on graphs, general trends recorded. Nearby examples of specific phenomena, such as variable stars, can be used to infer the behavior of more distant representatives; those distant yardsticks can be employed to measure other phenomena in that neighborhood, including the distance to a galaxy. Galileo Galilei recorded what he saw.
Since that time, observational astronomy has made steady advances with each improvement in telescope technology. A traditional division of observational astronomy is based on the region of the electromagnetic spectrum observed: Optical astronomy is the part of astronomy that uses optical instruments to observe light from near-infrared to near-ultraviolet wavelengths. Visible-light astronomy, using wavelengths detectable with the human eyes, falls in the middle of this spectrum. Infrared astronomy deals with the analysis of infrared radiation; the most common tool is the reflecting telescope, but with a detector sensitive to infrared wavelengths. Space telescopes are used at certain wavelengths where the atmosphere is opaque, or to eliminate noise. Radio astronomy detects radiation of millimetre to decametre wavelength; the receivers are similar to those used in radio broadcast transmission but much more sensitive. See Radio telescopes. High-energy astronomy includes X-ray astronomy, gamma-ray astronomy, extreme UV astronomy.
Occultation astronomy is the observation of the instant one celestial object occults or eclipses another. Multi-chord asteroid occultation observations measure the profile of the asteroid to the kilometre level. In addition to using electromagnetic radiation, modern astrophysicists can make observations using neutrinos, cosmic rays or gravitational waves. Observing a source using multiple methods is known as multi-messenger astronomy. Optical and radio astronomy can be performed with ground-based observatories, because the atmosphere is transparent at the wavelengths being detected. Observatories are located at high altitudes so as to minimise the absorption and distortion caused by the Earth's atmosphere; some wavelengths of infrared light are absorbed by water vapor, so many infrared observatories are located in dry places at high altitude, or in space. The atmosphere is opaque at the wavelengths used by X-ray astronomy, gamma-ray astronomy, UV astronomy and far infrared astronomy, so observations must be carried out from balloons or space observatories.
Powerful gamma rays can, however be detected by the large air showers they produce, the study of cosmic rays is a expanding branch of astronomy. For much of the history of observational astronomy all observation was performed in the visual spectrum with optical telescopes. While the Earth's atmosphere is transparent in this portion of the electromagnetic spectrum, most telescope work is still dependent on seeing conditions and air transparency, is restricted to the night time; the seeing conditions depend on thermal variations in the air. Locations that are cloudy or suffer from atmospheric turbulence limit the resolution of observations; the presence of the full Moon can brighten up the sky with scattered light, hindering observation of faint objects. For observation purposes, the optimal location for an optical telescope is undoubtedly in outer space. There the telescope can make observations without being affected by the atmosphere. However, at present it remains costly to lift telescopes into orbit.
Thus the next best locations are certain mountain peaks that have a high number of cloudless days and possess good atmospheric conditions. The peaks of the islands of Mauna Kea, Hawaii and La Palma possess these properties, as to a lesser extent do inland sites such as Llano de Chajnantor, Cerro Tololo and La Silla in Chile; these observatory locations have attracted an assemblage of powerful telescopes, totalling many billion US dollars of investment. The darkness of the night sky is an important factor in optical astronomy. With the size of cities and human populated areas expanding, the amount of artificial light at night has increased; these artificial lights produce a diffuse background illumination that makes observation of faint astronomical features difficult without special filters. In a few locations such as the state of Arizona and in the United Kingdom, this has led to campaigns for the reduction of light pollution; the use of hoods around street lights not only improves the amount of light directed toward the ground, but helps reduce the light directed toward the sky.
Atmospheric effects can hinder the resolution of a telescope. Without some means of correcting for the blurring effect of the shifting atmosphere, teles
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around 5,000 K or lower; the appearance of the red giant is from yellow-orange to red, including the spectral types K and M, but class S stars and most carbon stars. The most common red giants are stars on the red-giant branch that are still fusing hydrogen into helium in a shell surrounding an inert helium core. Other red giants are the red-clump stars in the cool half of the horizontal branch, fusing helium into carbon in their cores via the triple-alpha process. Red giants are stars that have exhausted the supply of hydrogen in their cores and have begun thermonuclear fusion of hydrogen in a shell surrounding the core, they have radii tens to hundreds of times larger than that of the Sun. However, their outer envelope is lower in temperature, giving them a reddish-orange hue. Despite the lower energy density of their envelope, red giants are many times more luminous than the Sun because of their great size.
Red-giant-branch stars have luminosities up to nearly three thousand times that of the Sun, spectral types of K or M, have surface temperatures of 3,000–4,000 K, radii up to about 200 times the Sun. Stars on the horizontal branch are hotter, with only a small range of luminosities around 75 L☉. Asymptotic-giant-branch stars range from similar luminosities as the brighter stars of the red giant branch, up to several times more luminous at the end of the thermal pulsing phase. Among the asymptotic-giant-branch stars belong the carbon stars of type C-N and late C-R, produced when carbon and other elements are convected to the surface in what is called a dredge-up; the first dredge-up occurs during hydrogen shell burning on the red-giant branch, but does not produce a large carbon abundance at the surface. The second, sometimes third, dredge up occurs during helium shell burning on the asymptotic-giant branch and convects carbon to the surface in sufficiently massive stars; the stellar limb of a red giant is not defined, contrary to their depiction in many illustrations.
Rather, due to the low mass density of the envelope, such stars lack a well-defined photosphere, the body of the star transitions into a'corona'. The coolest red giants have complex spectra, with molecular lines, emission features, sometimes masers from thermally pulsing AGB stars. Another noteworthy feature of red giants is that, unlike Sun-like stars whose photospheres have a large number of small convection cells, red-giant photospheres, as well as those of red supergiants, have just a few large cells, the features of which cause the variations of brightness so common on both types of stars. Red giants are evolved from main-sequence stars with masses in the range from about 0.3 M☉ to around 8 M☉. When a star forms from a collapsing molecular cloud in the interstellar medium, it contains hydrogen and helium, with trace amounts of "metals"; these elements are all uniformly mixed throughout the star. The star reaches the main sequence when the core reaches a temperature high enough to begin fusing hydrogen and establishes hydrostatic equilibrium.
Over its main sequence life, the star converts the hydrogen in the core into helium. For the Sun, the main-sequence lifetime is 10 billion years. More-massive stars burn disproportionately faster and so have a shorter lifetime than less massive stars; when the star exhausts the hydrogen fuel in its core, nuclear reactions can no longer continue and so the core begins to contract due to its own gravity. This brings additional hydrogen into a zone where the temperature and pressure are adequate to cause fusion to resume in a shell around the core; the outer layers of the star expand thus beginning the red-giant phase of the star's life. As the star expands, the energy produced in the burning shell of the star is spread over a much larger surface area, resulting in a lower surface temperature and a shift in the star's visible light output towards the red—hence it becomes a red giant. At this time, the star is said to be ascending the red-giant branch of the Hertzsprung–Russell diagram; the evolutionary path the star takes as it moves along the red-giant branch, which ends with the complete collapse of the core, depends on the mass of the star.
For the Sun and stars of less than about 2 M☉ the core will become dense enough that electron degeneracy pressure will prevent it from collapsing further. Once the core is degenerate, it will continue to heat until it reaches a temperature of 108 K, hot enough to begin fusing helium to carbon via the triple-alpha process. Once the degenerate core reaches this temperature, the entire core will begin helium fusion nearly in a so-called helium flash. In more-massive stars, the collapsing core will reach 108 K before it is dense enough to be degenerate, so helium fusion will begin much more smoothly, produce no helium flash; the core helium fusing phase of a star's life is called the horizontal branch in metal-poor stars, so named because these stars lie on a nearly horizontal line in the H–R diagram of many star clusters. Metal-rich helium-fusing stars instead lie on the so-called red clump in the H–R diagram. An analogous process oc
Cosmic ray
Cosmic rays are high-energy radiation originating outside the Solar System and from distant galaxies. Upon impact with the Earth's atmosphere, cosmic rays can produce showers of secondary particles that sometimes reach the surface. Composed of high-energy protons and atomic nuclei, they are originated either from the sun or from outside of our solar system. Data from the Fermi Space Telescope have been interpreted as evidence that a significant fraction of primary cosmic rays originate from the supernova explosions of stars. Active galactic nuclei appear to produce cosmic rays, based on observations of neutrinos and gamma rays from blazar TXS 0506+056 in 2018; the term ray is somewhat of a misnomer due to a historical accident, as cosmic rays were at first, wrongly, thought to be electromagnetic radiation. In common scientific usage, high-energy particles with intrinsic mass are known as "cosmic" rays, while photons, which are quanta of electromagnetic radiation are known by their common names, such as gamma rays or X-rays, depending on their photon energy.
In current usage, the term cosmic ray exclusively refers to massive particles – those that have rest mass – as opposed to photons, which have no rest mass, neutrinos, which have negligible rest mass. Massive particles have additional, mass-energy when they are moving, due to relativistic effects. Through this process, some particles acquire tremendously high mass-energies; these are higher than the photon energy of the highest-energy photons detected to date. The energy of the massless photon depends on frequency, not speed, as photons always travel at the same speed. At the higher end of the energy spectrum, relativistic kinetic energy is the main source of the mass-energy of cosmic rays; the highest-energy fermionic cosmic rays detected to date, such as the Oh-My-God particle, had an energy of about 3×1020 eV, while the highest-energy gamma rays to be observed, very-high-energy gamma rays, are photons with energies of up to 1014 eV, the highest energy neutrinos detected so far have energies of several 1015 eV.
Hence, the highest-energy detected fermionic cosmic rays are about 3×106 times as energetic as the highest-energy detected cosmic photons. Of primary cosmic rays, which originate outside of Earth's atmosphere, about 99% are the nuclei of well-known atoms, about 1% are solitary electrons. Of the nuclei, about 90% are simple protons; these fractions vary over the energy range of cosmic rays. A small fraction are stable particles of antimatter, such as positrons or antiprotons; the precise nature of this remaining fraction is an area of active research. An active search from Earth orbit for anti-alpha particles has failed to detect them. Cosmic rays attract great interest due to the damage they inflict on microelectronics and life outside the protection of an atmosphere and magnetic field, scientifically, because the energies of the most energetic ultra-high-energy cosmic rays have been observed to approach 3 × 1020 eV, about 40 million times the energy of particles accelerated by the Large Hadron Collider.
One can show that such enormous energies might be achieved by means of the centrifugal mechanism of acceleration in active galactic nuclei. At 50 J, the highest-energy ultra-high-energy cosmic rays have energies comparable to the kinetic energy of a 90-kilometre-per-hour baseball; as a result of these discoveries, there has been interest in investigating cosmic rays of greater energies. Most cosmic rays, however, do not have such extreme energies. After the discovery of radioactivity by Henri Becquerel in 1896, it was believed that atmospheric electricity, ionization of the air, was caused only by radiation from radioactive elements in the ground or the radioactive gases or isotopes of radon they produce. Measurements of increasing ionization rates at increasing heights above the ground during the decade from 1900 to 1910 could be explained as due to absorption of the ionizing radiation by the intervening air. In 1909, Theodor Wulf developed an electrometer, a device to measure the rate of ion production inside a hermetically sealed container, used it to show higher levels of radiation at the top of the Eiffel Tower than at its base.
However, his paper published in Physikalische Zeitschrift was not accepted. In 1911, Domenico Pacini observed simultaneous variations of the rate of ionization over a lake, over the sea, at a depth of 3 metres from the surface. Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth. In 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers to an altitude of 5,300 metres in a free balloon flight, he found the ionization rate increased fourfold over the rate at ground level. Hess ruled out the Sun as the radiation's source by making a balloon ascent during a near-total eclipse. With the moon blocking much of the Sun's visible radiation, Hess still measured rising radiation at rising altitudes, he concluded that "The results of the observations seem most to be explained by the assumption that radiation of high penetrating power enters from above into our atmosphere." In 1913–1914, Werner Kolhörster confirmed Victor Hess's earlier results by measuring the increased ionization enthalpy rate at an altitude of 9 km.
Hess received the Nobel Prize in Physics in 1936
Spitzer Space Telescope
The Spitzer Space Telescope the Space Infrared Telescope Facility, is an infrared space telescope launched in 2003 and still operating as of 2019. The planned mission period was to be 2.5 years with a pre-launch expectation that the mission could extend to five or more years until the onboard liquid helium supply was exhausted. This occurred on 15 May 2009. Without liquid helium to cool the telescope to the low temperatures needed to operate, most of the instruments are no longer usable. However, the two shortest-wavelength modules of the IRAC camera are still operable with the same sensitivity as before the cryogen was exhausted, have continued to be used to the present in the Spitzer Warm Mission. All Spitzer data, from both the primary and warm phases, are archived at the Infrared Science Archive. In keeping with NASA tradition, the telescope was renamed after its successful demonstration of operation, on 18 December 2003. Unlike most telescopes that are named after famous deceased astronomers by a board of scientists, the new name for SIRTF was obtained from a contest open to the general public.
The contest led to the telescope being named in honor of astronomer Lyman Spitzer, who had promoted the concept of space telescopes in the 1940s. Spitzer wrote a 1946 report for RAND Corporation describing the advantages of an extraterrestrial observatory and how it could be realized with available or upcoming technology, he has been cited for his pioneering contributions to rocketry and astronomy, as well as "his vision and leadership in articulating the advantages and benefits to be realized from the Space Telescope Program."The US$720 million Spitzer was launched on 25 August 2003 at 05:35:39 UTC from Cape Canaveral SLC-17B aboard a Delta II 7920H rocket. It follows a heliocentric instead of geocentric orbit and drifting away from Earth's orbit at 0.1 astronomical units per year. The primary mirror is 85 centimeters in diameter, f/12, made of beryllium and was cooled to 5.5 K. The satellite contains three instruments that allow it to perform astronomical imaging and photometry from 3.6 to 160 micrometers, spectroscopy from 5.2 to 38 micrometers, spectrophotometry from 5 to 100 micrometers.
By the early 1970s, astronomers began to consider the possibility of placing an infrared telescope above the obscuring effects of Earth's atmosphere. In 1979, a report from the National Research Council of the National Academy of Sciences, A Strategy for Space Astronomy and Astrophysics for the 1980s, identified a Space Infrared Telescope Facility as "one of two major astrophysics facilities for Spacelab", a Shuttle-borne platform. Anticipating the major results from an upcoming Explorer satellite and from the Shuttle mission, the report favored the "study and development of... long-duration spaceflights of infrared telescopes cooled to cryogenic temperatures." The launch in January 1983 of the Infrared Astronomical Satellite, jointly developed by the United States, the Netherlands, the United Kingdom, to conduct the first infrared survey of the sky, whetted the appetites of scientists worldwide for follow-up space missions capitalizing on the rapid improvements in infrared detector technology.
Earlier infrared observations had been made by both ground-based observatories. Ground-based observatories have the drawback that at infrared wavelengths or frequencies, both the Earth's atmosphere and the telescope itself will radiate strongly. Additionally, the atmosphere is opaque at most infrared wavelengths; this necessitates lengthy exposure times and decreases the ability to detect faint objects. It could be compared to trying to observe the stars at noon. Previous space observatories were launched during the 1980s and 1990s and great advances in astronomical technology have been made since then. Most of the early concepts envisioned repeated flights aboard the NASA Space Shuttle; this approach was developed in an era when the Shuttle program was expected to support weekly flights of up to 30 days duration. A May 1983 NASA proposal described SIRTF as a Shuttle-attached mission, with an evolving scientific instrument payload. Several flights were anticipated with a probable transition into a more extended mode of operation in association with a future space platform or space station.
SIRTF would be a 1-meter class, cryogenically cooled, multi-user facility consisting of a telescope and associated focal plane instruments. It would be launched on the Space Shuttle and remain attached to the Shuttle as a Spacelab payload during astronomical observations, after which it would be returned to Earth for refurbishment prior to re-flight; the first flight was expected to occur about 1990, with the succeeding flights anticipated beginning one year later. However, the Spacelab-2 flight aboard STS-51-F showed that the Shuttle environment was poorly suited to an onboard infrared telescope due to contamination from the "dirty" vacuum associated with the orbiters. By September 1983 NASA was considering the "possibility of a long duration SIRTF mission". Spitzer is the only one of the Great Observatories not launched by the Space Shuttle, as was intended. However, after the 1986 Challenger disaster, the Centaur LH2–LOX upper stage, which would have been required to place it in its final orbit, was banned from Shuttle use.
The mission underwent a series of redesigns during the 1990s due to budget considerations. This resulted in a much smaller but still capable mission that could use the smaller Delta II expendable launch vehicle. One of the most important
Water vapor
Water vapor, water vapour or aqueous vapor is the gaseous phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Unlike other forms of water, water vapor is invisible. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation, it triggers convection currents that can lead to clouds. Being a component of Earth's hydrosphere and hydrologic cycle, it is abundant in Earth's atmosphere where it is a potent greenhouse gas along with other gases such as carbon dioxide and methane. Use of water vapor, as steam, has been important to humans for cooking and as a major component in energy production and transport systems since the industrial revolution. Water vapor is a common atmospheric constituent, present in the solar atmosphere as well as every planet in the Solar System and many astronomical objects including natural satellites and large asteroids.
The detection of extrasolar water vapor would indicate a similar distribution in other planetary systems. Water vapor is significant in that it can be indirect evidence supporting the presence of extraterrestrial liquid water in the case of some planetary mass objects. Whenever a water molecule leaves a surface and diffuses into a surrounding gas, it is said to have evaporated; each individual water molecule which transitions between a more associated and a less associated state does so through the absorption or release of kinetic energy. The aggregate measurement of this kinetic energy transfer is defined as thermal energy and occurs only when there is differential in the temperature of the water molecules. Liquid water that becomes water vapor takes a parcel of heat with it, in a process called evaporative cooling; the amount of water vapor in the air determines how molecules will return to the surface. When a net evaporation occurs, the body of water will undergo a net cooling directly related to the loss of water.
In the US, the National Weather Service measures the actual rate of evaporation from a standardized "pan" open water surface outdoors, at various locations nationwide. Others do around the world; the US data is compiled into an annual evaporation map. The measurements range from under 30 to over 120 inches per year. Formulas can be used for calculating the rate of evaporation from a water surface such as a swimming pool. In some countries, the evaporation rate far exceeds the precipitation rate. Evaporative cooling is restricted by atmospheric conditions. Humidity is the amount of water vapor in the air; the vapor content of air is measured with devices known as hygrometers. The measurements are expressed as specific humidity or percent relative humidity; the temperatures of the atmosphere and the water surface determine the equilibrium vapor pressure. This condition is referred to as complete saturation. Humidity ranges from 0 gram per cubic metre in dry air to 30 grams per cubic metre when the vapor is saturated at 30 °C.
Sublimation is when water molecules directly leave the surface of ice without first becoming liquid water. Sublimation accounts for the slow mid-winter disappearance of ice and snow at temperatures too low to cause melting. Antarctica shows this effect to a unique degree because it is by far the continent with the lowest rate of precipitation on Earth; as a result, there are large areas where millennial layers of snow have sublimed, leaving behind whatever non-volatile materials they had contained. This is valuable to certain scientific disciplines, a dramatic example being the collection of meteorites that are left exposed in unparalleled numbers and excellent states of preservation. Sublimation is important in the preparation of certain classes of biological specimens for scanning electron microscopy; the specimens are prepared by cryofixation and freeze-fracture, after which the broken surface is freeze-etched, being eroded by exposure to vacuum till it shows the required level of detail.
This technique can display protein molecules, organelle structures and lipid bilayers with low degrees of distortion. Water vapour will only condense onto another surface when that surface is cooler than the dew point temperature, or when the water vapour equilibrium in air has been exceeded; when water vapour condenses onto a surface, a net warming occurs on that surface. The water molecule brings heat energy with it. In turn, the temperature of the atmosphere drops slightly. In the atmosphere, condensation produces clouds and precipitation; the dew point of an air parcel is the temperature to which it must cool before water vapour in the air begins to condense concluding water vapour is a type of water or rain. A net condensation of water vapour occurs on surfaces when the temperature of the surface is at or below the dew point temperature of the atmosphere. Deposition is a phase transition separate from condensation which leads to the direct formation of ice from water vapour. Frost and snow are examples of deposition.
There are many mechanism of cooling by which condensation occurs 1.direct loss of heat known as radiation cooling. 2.cooling with upliftment of air known as adiabatic cooling. There are 4 types of upliftment of air: a. orographic upliftment- mountains work as barrier for upliftment of air b. convectional upliftment- upliftment of air due to pressure difference c. frontal upliftment- upliftment of air due to temp difference d. cyclonic upliftment bu
Astronomer
An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, moons and galaxies – in either observational or theoretical astronomy. Examples of topics or fields astronomers study include planetary science, solar astronomy, the origin or evolution of stars, or the formation of galaxies. Related but distinct subjects like physical cosmology. Astronomers fall under either of two main types: observational and theoretical. Observational astronomers analyze the data. In contrast, theoretical astronomers create and investigate models of things that cannot be observed; because it takes millions to billions of years for a system of stars or a galaxy to complete a life cycle, astronomers must observe snapshots of different systems at unique points in their evolution to determine how they form and die. They use these data to create models or simulations to theorize how different celestial objects work.
Further subcategories under these two main branches of astronomy include planetary astronomy, galactic astronomy, or physical cosmology. Astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws. Today, that distinction has disappeared and the terms "astronomer" and "astrophysicist" are interchangeable. Professional astronomers are educated individuals who have a Ph. D. in physics or astronomy and are employed by research institutions or universities. They spend the majority of their time working on research, although they quite have other duties such as teaching, building instruments, or aiding in the operation of an observatory; the number of professional astronomers in the United States is quite small. The American Astronomical Society, the major organization of professional astronomers in North America, has 7,000 members; this number includes scientists from other fields such as physics and engineering, whose research interests are related to astronomy.
The International Astronomical Union comprises 10,145 members from 70 different countries who are involved in astronomical research at the Ph. D. beyond. Contrary to the classical image of an old astronomer peering through a telescope through the dark hours of the night, it is far more common to use a charge-coupled device camera to record a long, deep exposure, allowing a more sensitive image to be created because the light is added over time. Before CCDs, photographic plates were a common method of observation. Modern astronomers spend little time at telescopes just a few weeks per year. Analysis of observed phenomena, along with making predictions as to the causes of what they observe, takes the majority of observational astronomers' time. Astronomers who serve as faculty spend much of their time teaching undergraduate and graduate classes. Most universities have outreach programs including public telescope time and sometimes planetariums as a public service to encourage interest in the field.
Those who become astronomers have a broad background in maths and computing in high school. Taking courses that teach how to research and present papers are invaluable. In college/university most astronomers get a Ph. D. in astronomy or physics. While there is a low number of professional astronomers, the field is popular among amateurs. Most cities have amateur astronomy clubs that meet on a regular basis and host star parties; the Astronomical Society of the Pacific is the largest general astronomical society in the world, comprising both professional and amateur astronomers as well as educators from 70 different nations. Like any hobby, most people who think of themselves as amateur astronomers may devote a few hours a month to stargazing and reading the latest developments in research. However, amateurs span the range from so-called "armchair astronomers" to the ambitious, who own science-grade telescopes and instruments with which they are able to make their own discoveries and assist professional astronomers in research.
List of astronomers List of women astronomers List of Muslim astronomers List of French astronomers List of Hungarian astronomers List of Russian astronomers and astrophysicists List of Slovenian astronomers Dallal, Ahmad. "Science and Technology". In Esposito, John; the Oxford History of Islam. Oxford University Press, New York. ISBN 0-300-15911-0. Kennedy, E. S.. "A Survey of Islamic Astronomical Tables. 46. Philadelphia: American Philosophical Society. Toomer, Gerald. "Al-Khwārizmī, Abu Jaʿfar Muḥammad ibn Mūsā". In Gillispie, Charles Coulston. Dictionary of Scientific Biography. 7. New York: Charles Scribner's Sons. ISBN 0-684-16962-2. American Astronomical Society European Astronomical Society International Astronomical Union Astronomical Society of the Pacific Space's astronomy news
