1.
Mount Wilson Observatory
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The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 1, 740-metre peak in the San Gabriel Mountains near Pasadena, the observatory was conceived and founded by George Ellery Hale, who had previously built the 1 meter telescope at the Yerkes Observatory, then the worlds largest telescope. The Mount Wilson Solar Observatory was first funded by the Carnegie Institution of Washington in 1904, among the conditions of the lease was that it allow public access. There are three solar telescopes at Mount Wilson Observatory, today, just one of these telescopes, the 60 foot Solar Tower, is still used for solar research. The Snow Solar Telescope was the first telescope installed at the fledgling Mount Wilson Solar Observatory and it was the worlds first permanently mounted solar telescope. Solar telescopes had previously been portable so they could be taken to solar eclipses around the world, the telescope was donated to Yerkes Observatory by Helen Snow of Chicago. George Ellery Hale, then director of Yerkes, had the telescope brought to Mount Wilson to put it into service as a scientific instrument. Stellar research soon followed as the brightest stars could have their spectra recorded with very long exposures on glass plates, today the Snow solar telescope is mostly used by undergraduate students who get hands on training in solar physics and spectroscopy. It was also used publicly for the May 9,2016 transit of Mercury across the face of the sun, the 60-foot Solar Tower soon built on the work started at the Snow telescope. At its completion in 1908, the tower design of the 60 foot focal length solar telescope allowed much higher resolution of the solar image. The higher resolution came from situating the optics higher above the ground, on June 25,1908, Hale would record Zeeman splitting in the spectrum of a sunspot, showing for the first time that magnetic fields existed somewhere besides the earth. A later discovery was of the polarity in sunspots of the new solar cycle of 1912. The success of the 60 foot Tower prompted Hale to pursue yet another, taller tower telescope, in the 1960s, Robert Leighton discovered the sun had a 5-minute oscillation and the field of heliosiesmology was born. The 60 foot Tower is operated by the Department of Physics, the 150-foot focal length solar tower expanded on the solar tower design with its tower-in-a-tower design. An inner tower supports the optics above, while an outer tower and this design allowed complete isolation of the optics from the effect of wind swaying the tower. Two mirrors feed sunlight to a 12-inch lens which focuses light down at the ground floor and it was first completed in 1910, but unsatisfactory optics caused a two-year delay before a suitable doublet lens was installed. Research included solar rotation, sunspot polarities, daily sunspot drawings, the solar telescope would be the worlds largest for 50 years until the McMath-Pierce Solar telescope was completed at Kitt Peak in Arizona in 1962. In 1985, UCLA took over operation of the tower from the Carnegie Observatories after it was decided to stop funding the observatory
2.
Mount Wilson (California)
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The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 1, 740-metre peak in the San Gabriel Mountains near Pasadena, the observatory was conceived and founded by George Ellery Hale, who had previously built the 1 meter telescope at the Yerkes Observatory, then the worlds largest telescope. The Mount Wilson Solar Observatory was first funded by the Carnegie Institution of Washington in 1904, among the conditions of the lease was that it allow public access. There are three solar telescopes at Mount Wilson Observatory, today, just one of these telescopes, the 60 foot Solar Tower, is still used for solar research. The Snow Solar Telescope was the first telescope installed at the fledgling Mount Wilson Solar Observatory and it was the worlds first permanently mounted solar telescope. Solar telescopes had previously been portable so they could be taken to solar eclipses around the world, the telescope was donated to Yerkes Observatory by Helen Snow of Chicago. George Ellery Hale, then director of Yerkes, had the telescope brought to Mount Wilson to put it into service as a scientific instrument. Stellar research soon followed as the brightest stars could have their spectra recorded with very long exposures on glass plates, today the Snow solar telescope is mostly used by undergraduate students who get hands on training in solar physics and spectroscopy. It was also used publicly for the May 9,2016 transit of Mercury across the face of the sun, the 60-foot Solar Tower soon built on the work started at the Snow telescope. At its completion in 1908, the tower design of the 60 foot focal length solar telescope allowed much higher resolution of the solar image. The higher resolution came from situating the optics higher above the ground, on June 25,1908, Hale would record Zeeman splitting in the spectrum of a sunspot, showing for the first time that magnetic fields existed somewhere besides the earth. A later discovery was of the polarity in sunspots of the new solar cycle of 1912. The success of the 60 foot Tower prompted Hale to pursue yet another, taller tower telescope, in the 1960s, Robert Leighton discovered the sun had a 5-minute oscillation and the field of heliosiesmology was born. The 60 foot Tower is operated by the Department of Physics, the 150-foot focal length solar tower expanded on the solar tower design with its tower-in-a-tower design. An inner tower supports the optics above, while an outer tower and this design allowed complete isolation of the optics from the effect of wind swaying the tower. Two mirrors feed sunlight to a 12-inch lens which focuses light down at the ground floor and it was first completed in 1910, but unsatisfactory optics caused a two-year delay before a suitable doublet lens was installed. Research included solar rotation, sunspot polarities, daily sunspot drawings, the solar telescope would be the worlds largest for 50 years until the McMath-Pierce Solar telescope was completed at Kitt Peak in Arizona in 1962. In 1985, UCLA took over operation of the tower from the Carnegie Observatories after it was decided to stop funding the observatory
3.
Geographic coordinate system
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A geographic coordinate system is a coordinate system used in geography that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are chosen such that one of the numbers represents a vertical position. A common choice of coordinates is latitude, longitude and elevation, to specify a location on a two-dimensional map requires a map projection. The invention of a coordinate system is generally credited to Eratosthenes of Cyrene. Ptolemy credited him with the adoption of longitude and latitude. Ptolemys 2nd-century Geography used the prime meridian but measured latitude from the equator instead. Mathematical cartography resumed in Europe following Maximus Planudes recovery of Ptolemys text a little before 1300, in 1884, the United States hosted the International Meridian Conference, attended by representatives from twenty-five nations. Twenty-two of them agreed to adopt the longitude of the Royal Observatory in Greenwich, the Dominican Republic voted against the motion, while France and Brazil abstained. France adopted Greenwich Mean Time in place of local determinations by the Paris Observatory in 1911, the latitude of a point on Earths surface is the angle between the equatorial plane and the straight line that passes through that point and through the center of the Earth. Lines joining points of the same latitude trace circles on the surface of Earth called parallels, as they are parallel to the equator, the north pole is 90° N, the south pole is 90° S. The 0° parallel of latitude is designated the equator, the plane of all geographic coordinate systems. The equator divides the globe into Northern and Southern Hemispheres, the longitude of a point on Earths surface is the angle east or west of a reference meridian to another meridian that passes through that point. All meridians are halves of great ellipses, which converge at the north and south poles, the prime meridian determines the proper Eastern and Western Hemispheres, although maps often divide these hemispheres further west in order to keep the Old World on a single side. The antipodal meridian of Greenwich is both 180°W and 180°E, the combination of these two components specifies the position of any location on the surface of Earth, without consideration of altitude or depth. The grid formed by lines of latitude and longitude is known as a graticule, the origin/zero point of this system is located in the Gulf of Guinea about 625 km south of Tema, Ghana. To completely specify a location of a feature on, in, or above Earth. Earth is not a sphere, but a shape approximating a biaxial ellipsoid. It is nearly spherical, but has an equatorial bulge making the radius at the equator about 0. 3% larger than the radius measured through the poles, the shorter axis approximately coincides with the axis of rotation
4.
Observatory
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An observatory is a location used for observing terrestrial or celestial events. Astronomy, climatology/meteorology, geology, oceanography and volcanology are examples of disciplines for which observatories have been constructed, historically, observatories were as simple as containing an astronomical sextant or Stonehenge. Astronomical observatories are mainly divided into four categories, space based, airborne, ground based, ground-based observatories, located on the surface of Earth, are used to make observations in the radio and visible light portions of the electromagnetic spectrum. Most optical telescopes are housed within a dome or similar structure, Telescope domes have a slit or other opening in the roof that can be opened during observing, and closed when the telescope is not in use. In most cases, the upper portion of the telescope dome can be rotated to allow the instrument to observe different sections of the night sky. Radio telescopes usually do not have domes, for optical telescopes, most ground-based observatories are located far from major centers of population, to avoid the effects of light pollution. The ideal locations for modern observatories are sites that have dark skies, a percentage of clear nights per year, dry air. At high elevations, the Earths atmosphere is thinner, thereby minimizing the effects of atmospheric turbulence, sites that meet the above criteria for modern observatories include the southwestern United States, Hawaii, Canary Islands, the Andes, and high mountains in Mexico such as Sierra Negra. Major optical observatories include Mauna Kea Observatory and Kitt Peak National Observatory in the USA, Roque de los Muchachos Observatory in Spain, and Paranal Observatory in Chile. Specific research study performed in 2009 shows that the best possible location for ground-based observatory on Earth is Ridge A — a place in the part of Eastern Antarctica. This location provides the least atmospheric disturbances and best visibility, beginning in 1930s, radio telescopes have been built for use in the field of radio astronomy to observe the Universe in the radio portion of the electromagnetic spectrum. Since the mid-20th century, a number of observatories have been constructed at very high altitudes, above 4. The largest and most notable of these is the Mauna Kea Observatory, the Chacaltaya Astrophysical Observatory in Bolivia, at 5,230 m, was the worlds highest permanent astronomical observatory from the time of its construction during the 1940s until 2009. It has now surpassed by the new University of Tokyo Atacama Observatory. As a result, the resolution of space telescopes such as the Hubble Space Telescope is often much smaller than a ground-based telescope with a similar aperture. However, all these advantages do come with a price, Space telescopes are much more expensive to build than ground-based telescopes. Due to their location, space telescopes are also difficult to maintain. The Hubble Space Telescope was serviced by the Space Shuttle while many other space telescopes cannot be serviced at all, Airborne observatories have the advantage of height over ground installations, putting them above most of the Earths atmosphere
5.
Los Angeles County, California
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Los Angeles County, officially the County of Los Angeles, is the most populous county in both the United States and the state of California, the countrys most populous state. Its population is larger than that of 42 individual U. S. states and it has 88 incorporated cities and many unincorporated areas and at 4,083 square miles, it is larger than the combined areas of the U. S. states of Delaware and Rhode Island. The county is home to more than one-quarter of California residents and is one of the most ethnically diverse counties in the U. S and its county seat, the City of Los Angeles, is also its most populous city at about four million. Los Angeles County is one of the counties of California. The county originally included parts of what are now Kern, San Bernardino, Riverside, as the population increased, sections were split off to organize San Bernardino County in 1853, Kern County in 1866, and Orange County in 1889. According to the U. S. Census Bureau, the county has an area of 4,751 square miles, Los Angeles County borders 70 miles of coast on the Pacific Ocean and encompasses mountain ranges, valleys, forests, islands, lakes, rivers, and desert. The western extent of the Mojave Desert begins in the Antelope Valley, most of the population of Los Angeles County is located in the south and southwest, with major population centers in the Los Angeles Basin, San Fernando Valley and San Gabriel Valley. Other population centers are found in the Santa Clarita Valley, Pomona Valley, Crescenta Valley, the county is divided west-to-east by the San Gabriel Mountains, which are part of the Transverse Ranges of southern California, and are contained mostly within the Angeles National Forest. Los Angeles County includes San Clemente Island and Santa Catalina Island, non-Hispanic whites numbered 2,728,321, or 28% of the population. Hispanic or Latino residents of any race numbered 4,687,889, 36% of Los Angeles Countys population was of Mexican ancestry,3. 7% Salvadoran, and 2. 2% Guatemalan heritage. The largest Asian groups of the 1,346,865 Asians in Los Angeles County are 4. 0% Chinese,3. 3% Filipino,2. 2% Korean,1. 0% Japanese,0. 9% Vietnamese,0. 8% Indian, and 0. 3% Cambodian. The racial makeup of the county is 48. 7% White,11. 0% African American,0. 8% Native American,10. 0% Asian,0. 3% Pacific Islander,23. 5% from other races, and 4. 9% from two or more races. 44. 6% of the population are Hispanic or Latino of any race, the largest European-American ancestry groups are German, Irish, English and Italian. 45. 9% of the population reported speaking only English at home,37. 9% spoke Spanish,2. 22% Tagalog,2. 0% Chinese,1. 9% Korean,1. 87% Armenian,0. 5% Arabic, and 0. 2% Hindi. At the census of 2000, there were 9,519,338 people,3,133,774 households, the population density was 2,344 people per square mile. There were 3,270,909 housing units at a density of 806 per square mile. 25% of all households were made up of individuals and 7% had someone living alone who was 65 years of age or older, the average household size was 2.98 and the average family size was 3.61. In the county, the population was out with 28% under the age of 18, 10% from 18 to 24, 33% from 25 to 44, 19% from 45 to 64
6.
San Gabriel Mountains
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The San Gabriel Mountains are a mountain range located in northern Los Angeles County and western San Bernardino County, California, United States. The mountain range is part of the Transverse Ranges and lies between the Los Angeles Basin and the Mojave Desert, with Interstate 5 to the west and Interstate 15 to the east. This range lies in, and is surrounded by, the Angeles National Forest, the highest peak in the range is Mount San Antonio, commonly referred to as Mt. Baldy. Mount Wilson is another peak, famed for the Mount Wilson Observatory. The observatory may be visited by the public, on October 10,2014, President Obama designated the area the San Gabriel Mountains National Monument. Much of the range features rolling peaks, the range lacks craggy features, but contains a large number of canyons and is generally very rugged and difficult to traverse. The San Gabriel Mountains are in effect a large block that was uplifted and then dissected by numerous rivers. North of San Fernando, the San Gabriel Mountains crest abruptly up to almost 4,000 feet, pacoima and Big Tujunga Canyons cut through the range just east of San Fernando, carrying runoff into the San Fernando Valley. Little Tujunga Canyon Road bridges the range in area, connecting the San Fernando Valley to the Santa Clara River valley in the north. Towering over Big Tujunga Canyon north of Big Tujunga Reservoir is Mount Gleason, which at 6,502 feet, is the highest in this region of the San Gabriels. South of the gorge are the foothills of the mountains, which rise abruptly 4,000 feet above the Los Angeles Basin and give rise to the Arroyo Seco. Southeast of Big Tujunga Canyon, the front range of the San Gabriels gradually grows in elevation. On the north the range is dissected by the canyon of the West Fork San Gabriel River. On the north slopes of the San Gabriel crest, the ranks of mountains drop down incrementally to the floor of the Mojave Desert in a much more gradual manner than the sheer southern flank. The Angeles Crest Highway, one of the routes across the San Gabriels. Little Rock, Big Rock and Sheep Creeks drain off the part of the mountains. To the east, the San Andreas Fault cuts across the range, forming a series of long, straight and narrow depressions, including Swarthout Valley, South of Mount San Antonio, San Antonio Creek drains the mountains, cutting the deep San Antonio Canyon. However, there are several notable peaks in this region, including Telegraph Peak, at 8,985 feet, Cucamonga Peak, at 8,859 feet
7.
Pasadena, California
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Pasadena /ˌpæsəˈdiːnə/ is a city in Los Angeles County, California, United States. As of 2013, the population of Pasadena was 139,731. Pasadena is the ninth-largest city in Los Angeles County, Pasadena was incorporated on June 19,1886, becoming one of the first cities be incorporated in what is now Los Angeles County, the only one being incorporated earlier being its namesake. It is one of the cultural centers of the San Gabriel Valley. The city is known for hosting the annual Rose Bowl football game, the original inhabitants of Pasadena and surrounding areas were members of the Native American Hahamog-na tribe, a branch of the Tongva Nation. They spoke the Tongva language and had lived in the Los Angeles Basin for thousands of years, Tongva dwellings lined the Arroyo Seco in present day Pasadena and south to where it joins the Los Angeles River and along other natural waterways in the city. The native people lived in thatched, dome-shape lodges and they lived on a diet of acorn meal, seeds and herbs, venison, and other small animals. They traded for fish with the coastal Tongva. They made cooking vessels from steatite soapstone from Catalina Island, the trail has been in continuous use for thousands of years. An arm of the trail is still in use in what is now known as Salvia Canyon. When the Spanish occupied the Los Angeles Basin they built the San Gabriel Mission and renamed the local Tongva people Gabrielino Indians, today, several bands of Tongva people live in the Los Angeles area. The Rancho comprised the lands of todays communities of Pasadena, Altadena, before the annexation of California in 1848, the last of the Mexican owners was Manuel Garfias who retained title to the property after statehood in 1850. Garfias sold sections of the property to the first Anglo settlers to come into the area, Dr. Benjamin Eaton, the father of Fred Eaton, much of the property was purchased by Benjamin Wilson, who established his Lake Vineyard property in the vicinity. Wilson, known as Don Benito to the local Indians, also owned the Rancho Jurupa and was mayor of Los Angeles and he was the grandfather of WWII General George S. Patton, Jr. and the namesake of Mount Wilson. Berry was an asthmatic and claimed that he had his best three nights sleep at Rancho San Pascual, to keep the find a secret, Berry code-named the area Muscat after the grape that Wilson grew. To raise funds to bring the company of people to San Pascual, Berry formed the Southern California Orange and Citrus Growers Association and sold stock in it. The newcomers were able to purchase a portion of the property along the Arroyo Seco and on January 31,1874. As a gesture of good will, Wilson added 2,000 acres of then-useless highland property, at the time, the Indiana Colony was a narrow strip of land between the Arroyo Seco and Fair Oaks Avenue
8.
Inversion (meteorology)
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In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to an inversion, i. e. an increase in temperature with height. An inversion can lead to such as smog being trapped close to the ground. An inversion can also suppress convection by acting as a cap, if this cap is broken for any of several reasons, convection of any moisture present can then erupt into violent thunderstorms. Temperature inversion can notoriously result in freezing rain in cold climates. g, given the right conditions, the normal vertical temperature gradient is inverted such that the air is colder near the surface of the Earth. This can occur when, for example, a warmer, less-dense air mass moves over a cooler, denser air mass. This type of inversion occurs in the vicinity of warm fronts, with sufficient humidity in the cooler layer, fog is typically present below the inversion cap. This effect is virtually confined to regions as the ocean retains heat far longer. In the polar regions during winter, inversions are nearly always present over land, a warmer air mass moving over a cooler one can shut off any convection which may be present in the cooler air mass. This is known as a capping inversion, such capping inversions typically precede the development of tornadoes in the Midwestern United States. In this instance, the layer is actually quite warm. An inversion can develop aloft as a result of air gradually sinking over an area and being warmed by adiabatic compression. A stable marine layer may develop over the ocean as a result. The accumulated smog and dust under the inversion quickly taints the sky reddish and this can become a problem in cities where many pollutants exist. During a severe inversion, trapped air pollutants form a haze that can cause respiratory problems. The Great Smog of 1952 in London, England, is one of the most serious examples of such an inversion and it was blamed for an estimated 11,000 to 12,000 deaths. Sometimes the inversion layer is at a high altitude that cumulus clouds can condense. This decreases the amount of sunlight reaching the ground and prevents new thermals from forming, as the clouds disperse, sunny weather replaces cloudiness in a cycle that can occur more than once a day
9.
Smog
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Smog is a type of air pollutant. The word smog was coined in the early 20th century as a portmanteau of the smoke and fog to refer to smoky fog, its opacity. The word was then intended to refer to what was known as pea soup fog. This kind of air pollution is composed of nitrogen oxides, sulfur oxides, ozone. Human-made smog is derived from coal emissions, vehicular emissions, industrial emissions, forest and agricultural fires, in certain other cities, such as Delhi, smog severity is often aggravated by stubble burning in neighboring agricultural areas. The atmospheric pollution levels of Los Angeles, Beijing, Delhi, Mexico City, Tehran and it is usually highly toxic to humans and can cause severe sickness, shortened life or death. Coinage of the smog is generally attributed to Dr. Henry Antoine Des Voeux in his 1905 paper, Fog. The following day the newspaper stated that Dr. Des Voeux did a service in coining a new word for the London fog. However, this is predated by a Los Angeles Times article of January 19,1893, coal fires, used to heat individual buildings or in a power-producing plant, can emit significant clouds of smoke that contributes to smog. Air pollution from this source has reported in England since the Middle Ages. London, in particular, was notorious up through the century for its coal-caused smogs. Traffic emissions – such as trucks, buses, and automobiles – also contribute. Airborne by-products from vehicle exhaust systems cause air pollution and are an ingredient in the creation of smog in some large cities. The major culprits from transportation sources are carbon monoxide, nitrogen oxides, volatile compounds, sulfur dioxide. These molecules react with sunlight, heat, ammonia, moisture, and other compounds to form the noxious vapors, ground level ozone, Photochemical smog is the chemical reaction of sunlight, nitrogen oxides and volatile organic compounds in the atmosphere, which leaves airborne particles and ground-level ozone. A secondary pollutant is not directly emitted as such, but forms when other pollutants react in the atmosphere, all of these harsh chemicals are usually highly reactive and oxidizing. Photochemical smog is therefore considered to be a problem of modern industrialization and it is present in all modern cities, but it is more common in cities with sunny, warm, dry climates and a large number of motor vehicles. Because it travels with the wind, it can affect sparsely populated areas as well, the composition and chemical reactions involved in photochemical smog were not understood until the 1950s
10.
Interferometry
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Interferometry is a family of techniques in which waves, usually electromagnetic waves, are superimposed causing the phenomenon of interference in order to extract information. Interferometers are widely used in science and industry for the measurement of small displacements, refractive index changes, in an interferometer, light from a single source is split into two beams that travel different optical paths, then combined again to produce interference. The resulting interference fringes give information about the difference in path length, waves which are not completely in phase nor completely out of phase will have an intermediate intensity pattern, which can be used to determine their relative phase difference. Most interferometers use light or some form of electromagnetic wave. Typically a single incoming beam of coherent light will be split into two beams by a beam splitter. Each of these beams travels a different route, called a path, the path difference, the difference in the distance traveled by each beam, creates a phase difference between them. It is this phase difference that creates the interference pattern between the initially identical waves. If a single beam has been split along two paths, then the difference is diagnostic of anything that changes the phase along the paths. This could be a change in the path length itself or a change in the refractive index along the path. As seen in Fig. 2a and 2b, the observer has a view of mirror M1 seen through the beam splitter. The fringes can be interpreted as the result of interference between light coming from the two virtual images S1 and S2 of the original source S, the characteristics of the interference pattern depend on the nature of the light source and the precise orientation of the mirrors and beam splitter. In Fig. 2a, the elements are oriented so that S1 and S2 are in line with the observer. Use of white light will result in a pattern of colored fringes, the central fringe representing equal path length may be light or dark depending on the number of phase inversions experienced by the two beams as they traverse the optical system. Interferometers and interferometric techniques may be categorized by a variety of criteria, In homodyne detection, the phase difference between the two beams results in a change in the intensity of the light on the detector. The resulting intensity of the light after mixing of two beams is measured, or the pattern of interference fringes is viewed or recorded. Most of the interferometers discussed in this article fall into this category, the heterodyne technique is used for shifting an input signal into a new frequency range as well as amplifying a weak input signal. A weak input signal of frequency f1 is mixed with a reference frequency f2 from a local oscillator. The nonlinear combination of the input signals creates two new signals, one at the sum f1 + f2 of the two frequencies, and the other at the difference f1 − f2 and these new frequencies are called heterodynes
11.
Light pollution
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Light pollution, also known as photopollution, is excessive, misdirected or obtrusive artificial light. As a major side-effect of urbanization, it is blamed for compromising health, disrupting ecosystems, Light pollution is the adding-of/added light itself, in analogy to added sound, carbon dioxide, etc. Adverse consequences are multiple, some of them may not be known yet, scientific definitions thus include the following, The degradation of photic habitat by artificial light. The alteration of light levels in the outdoor environment owing to artificial light sources. The alteration of light levels in the environment due to man-made sources of light. Indoor light pollution is such alteration of light levels in the environment due to sources of light. The introduction by humans, directly or indirectly, of light into the environment. The first three of the four scientific definitions describe the state of the environment. The fourth one describes the process of polluting by light, Light pollution is a side effect of industrial civilization. Its sources include building exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, since the early 1980s, a global dark-sky movement has emerged, with concerned people campaigning to reduce the amount of light pollution. The International Dark-Sky Association is one non-profit advocacy group involved in this movement, several industry groups also recognize light pollution as an important issue. For example, the Institution of Lighting Engineers in the United Kingdom provides its members with information about light pollution, the problems it causes, and how to reduce its impact. Since not everyone is irritated by the same lighting sources, it is common for one persons light pollution to be light that is desirable for another. One example of this is found in advertising, when an advertiser wishes for particular lights to be bright and visible, other types of light pollution are more certain. For instance, light that crosses a property boundary and annoys a neighbor is generally wasted. Where objective measurement is desired, light levels can be quantified by field measurement or mathematical modeling, authorities have also taken a variety of measures for dealing with light pollution, depending on the interests, beliefs and understandings of the society involved. Measures range from doing nothing at all, to implementing strict laws, Light pollution is a broad term that refers to multiple problems, all of which are caused by inefficient, unappealing, or unnecessary use of artificial light. Specific categories of light pollution include light trespass, over-illumination, glare, light clutter, a single offending light source often falls into more than one of these categories
12.
George Ellery Hale
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George Ellery Hale was born on June 29,1868 in Chicago, Illinois to William Ellery Hale and Mary Browne. He is descended from Thomas Hale of Watton-on-Stone, Hertfordshire, England and his father acquired a considerable fortune manufacturing and installing passenger elevators during the reconstruction of Chicago, which had been destroyed in the Great Chicago Fire of 1871. He spent his youth fascinated by the books and machinery given to him by his parents—one of his most prized possessions was a small microscope, with his fathers encouragement, he built a small shop in their house that turned into a laboratory. The microscope led to his interest in optics, at the age of fourteen, George built his first telescope. His father later replaced it with a second-hand Clark refractor that they mounted on the roof of their Kenwood house, soon he was photographing the night skies, observing a partial eclipse of the sun, and drawing sun-spots. As an avid reader with a strong interest in the field of astrophysics, Hale was drawn to the writings of William Huggins, Norman Lockyer. His fascination with science, however, did not preclude interests more typical of a boy, such as fishing, boating, swimming, skating, tennis. He was a reader of the stories of Jules Verne—particularly drawn to the tales of adventure set in the mountains of California. Hale spent summers at his grandmothers house in the old New England village of Madison, Connecticut, after graduating from Oakland Public School in Chicago, Hale attended the Allen Academy, where he studied chemistry, physics, and astronomy. He supplemented his practical experience by attending a course in shop-work at the Chicago Manual Training School. During these years, Hale developed a knowledge of the principles of architecture and city planning with the help of his fathers friend, upon Burnhams advice and encouragement, Hale decided at the age of seventeen to continue his education at the Massachusetts Institute of Technology. Hale was educated at MIT, at the Harvard College Observatory, as an undergraduate at MIT, he is known for inventing the spectroheliograph, with which he made his discovery of solar vortices. In 1908, he used the Zeeman effect with a modified spectroheliograph to establish that sunspots were magnetic and this systematic property of sunspot magnetic fields is now commonly referred to as the Hale–Nicholson law, or in many cases simply Hales law. He was coeditor of Astronomy and Astrophysics, 1892–95, and after 1895 editor of the Astrophysical Journal and he also served on the board of trustees for Science Service, now known as Society for Science & the Public, from 1921 to 1923. Hale replied in November, saying that such observations could be done only during an eclipse of the sun. At Mount Wilson, he hired and encouraged Harlow Shapley and Edwin Hubble toward some of the most significant discoveries of the time and he was a prolific organizer who helped create a number of astronomical institutions, societies and journals. Hale also played a role in developing the California Institute of Technology into a leading research university. After retiring as director at Mount Wilson, he built the Hale Solar Laboratory in Pasadena, California, as his office and workshop, from early youth, Hale had been internationally oriented, travelling widely throughout Europe in his younger years
13.
Yerkes Observatory
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Yerkes Observatory is an astronomical observatory in Williams Bay, Wisconsin operated by the University of Chicago Department of Astronomy and Astrophysics. The observatory, which calls itself the birthplace of modern astrophysics, was founded in 1897 by astronomer George Ellery Hale, the observatory houses a 40 refracting telescope, the largest ever successfully used for astronomy. And a collection of over 170,000 photographic plates, the director of the observatory is Doyle Al Harper. Yerkes Observatorys 100 cm refracting telescope was built by the refracting telescope company Alvan Clark & Sons and it is the largest refracting telescope used for scientific research. The mounting and tube for the 100-centimeter telescope was exhibited at the 1893 Worlds Columbian Exposition in Chicago before being installed in the observatory, the grinding of the lens was completed later. The observatory also houses 100 cm and 61 cm reflecting telescopes, several smaller telescopes are used for educational purposes. Research conducted at Yerkes includes work on the medium, globular cluster formation, infrared astronomy. The University of Chicago also maintains a center in the observatory. In 2012 the engineers completed work on the High-resolution Airborne Wideband Camera, researchers also use the Yerkes collection of over 170,000 archival photographic plates that date back to the 1890s. In March 2005, the University of Chicago announced plans to sell the observatory, two purchasers had expressed an interest, Mirbeau, an East Coast developer that wanted to build luxury homes, and Aurora University, which has a campus straddling the Williams Bay property. About 70 homes were to be developed on the upper Yerkes property surrounding the historic observatory and these grounds had been designed more than 100 years previously by John Olmsted, the brother of famed landscape architect Frederick Law Olmsted, designer of New Yorks Central Park. Ultimately, Williams Bays refusal to change the zoning from education to residential caused Mirbeau to abandon its development plans, in view of the public controversy surrounding the development proposals, the university suspended these plans in January 2007. The study group began its work in February 2007 and issued its final report November 30,2007 and it also suggested that some lakefront and woods parcels could be sold for residential development. List of largest optical refracting telescopes List of observatories Media related to Yerkes Observatory at Wikimedia Commons Yerkes Observatory, description and history from the National Park Service. Save Yerkes Yerkes Study Group Geneva Lake Conservancy
14.
Solar telescope
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A solar telescope is a special purpose telescope used to observe the Sun. Solar telescopes usually detect light with wavelengths in, or not far outside, obsolete names for sun telescopes include heliograph and photoheliograph. Solar telescopes need optics large enough to achieve the best possible diffraction limit, however, recently newer narrower filters and higher framerates have also driven solar telescopes towards photon-starved operations. Both the European Solar Telescope as well as the Advanced Technology Solar Telescope have larger apertures not only to increase the resolution, to alleviate this, solar telescopes are usually built on towers and the structures are painted white. The Dutch Open Telescope is built on a framework to allow the wind to pass through the complete structure. Another solar telescope-specific problem is the heat generated by the tightly-focused sunlight, for this reason, a heat stop is an integral part of the design of solar telescopes. For the upcoming ATST, the load is 2.5 MW/m2. The goal of such a stop is not only to survive this heat load. However, this is not possible for apertures over 1 meter, therefore, the EST and ATST have active cooling of the dome to minimize the temperature difference between the air inside and outside the telescope. Because the Sun travels on a fixed path across the sky, some solar telescopes are fixed in position. One example of this is the McMath-Pierce Solar Telescope, the Einstein Tower became operational in 1924 McMath-Pierce Solar Telescope McMath-Hulbert Observatory Swedish Vacuum Solar Telescope Swedish 1-m Solar Telescope Richard B. Advanced Technology Solar Telescope, a telescope with 4m aperture. European Solar Telescope, a future 4-meter class aperture telescope, national Large Solar Telescope, is a Gregorian multi-purpose open telescope proposed to be built and Installed in India and aims to study the suns microscopic structure. The Radio Solar Telescope Network is a network of solar observatories maintained and operated by the U. S. Air Force Weather Agency. CERN Axion Solar Telescope, looks for solar axions in the early 2000s In the field of astronomy there are many methods used to observe the sun. In contrast to professional telescopes, amateur solar telescopes are much smaller. List of solar telescopes List of telescope types Heliostat Solar telescopes, Wolfgang Schmidt, doi,10. 4249/scholarpedia.4333 CSIRO Solar Heliograph part 2 Solar Gallery of an amateur astronomer Solar Gallery of the Hong Kong Astronomical Society Lawrence, Pete
15.
Zeeman splitting
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The Zeeman effect, named after the Dutch physicist Pieter Zeeman, is the effect of splitting a spectral line into several components in the presence of a static magnetic field. It is analogous to the Stark effect, the splitting of a line into several components in the presence of an electric field. Also similar to the Stark effect, transitions between different components have, in general, different intensities, with some being entirely forbidden, the Zeeman effect is very important in applications such as nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, magnetic resonance imaging and Mössbauer spectroscopy. It may also be utilized to improve accuracy in atomic absorption spectroscopy, a theory about the magnetic sense of birds assumes that a protein in the retina is changed due to the Zeeman effect. When the spectral lines are lines, the effect is called inverse Zeeman effect. Historically, one distinguishes between the normal and an anomalous Zeeman effect, the anomalous effect appears on transitions where the net spin of the electrons is an odd half-integer, so that the number of Zeeman sub-levels is even. It was called anomalous because the spin had not yet been discovered. At higher magnetic fields the effect ceases to be linear, at even higher field strength, when the strength of the external field is comparable to the strength of the atoms internal field, electron coupling is disturbed and the spectral lines rearrange. This is called the Paschen-Back effect, in the modern scientific literature, these terms are rarely used, with a tendency to use just the Zeeman effect. The magnetic moment consists of the electronic and nuclear parts, however, therefore, μ → ≈ − μ B g J → ℏ, where μ B is the Bohr magneton, J → is the total electronic angular momentum, and g is the Landé g-factor.0023192. If the interaction term V M is small, it can be treated as a perturbation, in the Paschen-Back effect, described below, V M exceeds the LS coupling significantly. In ultrastrong magnetic fields, the interaction may exceed H0, in which case the atom can no longer exist in its normal meaning. There are, of course, intermediate cases which are more complex than these limit cases. If the spin-orbit interaction dominates over the effect of the magnetic field, L → and S → are not separately conserved. The spin and orbital angular momentum vectors can be thought of as precessing about the angular momentum vector J →. Thus, ⟨ V M ⟩ = μ B ℏ J → ⋅ B →, in the presence of an external magnetic field, the weak-field Zeeman effect splits the 1S1/2 and 2P1/2 levels into 2 states each and the 2P3/2 level into 4 states. Note in particular that the size of the splitting is different for the different orbitals. On the left, fine structure splitting is depicted and this splitting occurs even in the absence of a magnetic field, as it is due to spin-orbit coupling
16.
Kitt Peak
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Kitt Peak is a mountain in the U. S. state of Arizona, and at 6,883 feet is the highest point in the Quinlan Mountains. It is the location of the Kitt Peak National Observatory, the radio telescope at the Observatory is one of ten dishes comprising the Very Long Baseline Array radio telescope. The peak was named in English by County Surveyor George J. Roskruge for his sister, Phillippa, on his 1893 Pima County Survey map, Roskruge spelled the name Kits. At the request of the wife of George F. Kitt, Kitt Peak is the second-highest peak on the Tohono Oodham Indian reservation, and as such is the second-most sacred after Baboquivari Peak. Near the summit is Iitois Garden, the residence of the nations elder brother deity. The name Ioligam means red stick in reference to the abundance of bushes on
17.
Hale Telescope
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The Hale Telescope is a 200-inch, f/3.3 reflecting telescope at the Palomar Observatory in California, US, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation, he orchestrated the planning, design, and construction of the observatory and it is still in active use. It was the largest optical telescope in the world from its completion in 1948 until the BTA-6 was built in 1976, the chief optical designer for Hales previous 100-inch telescope was George Willis Ritchey, who intended the new telescope to be of Ritchey–Chrétien design. Compared to the parabolic primary, this design would have provided sharper images over a larger usable field of view. However, Ritchey and Hale had a falling out, with the project already late and over budget, Hale refused to adopt the new design, with its complex curvatures, and Ritchey left the project. The Mount Palomar Hale telescope turned out to be the last world-leading telescope to have a primary mirror. The Corning Glass Works was assigned the task of making a 200-inch primary mirror, construction of the observatory facilities and dome started in 1936, but because of interruptions caused by World War II, the telescope was not completed until 1948 when it was dedicated. Due to slight distortions of images, corrections were made to the telescope throughout 1949 and it became available for research in 1950. The 200-inch Hale saw first light on January 26,1949 under the direction of American astronomer Edwin Powell Hubble, targeting NGC2261, the photographs made then were published in the astronomical literature and in the May 7,1949 issue of Colliers Magazine. It is equipped with optical and infrared array imagers, spectrographs. It has also used lucky cam imaging, which in combination with adaptive optics pushed the mirror close to its resolution for certain types of viewing. One of the Corning Labs glass test blanks for the Hale was used for the C. Donald Shane telescopes 120-inch primary mirror, the collecting area of the Hale is about 31,000 square inches. The optical tube assembly uses a Serrurier truss, then newly invented by Mark U, Serrurier of Caltech in Pasadena in 1935, designed to flex in such a way as to keep all of the optics in alignment. Theodore von Karman designed the system to avoid potential issues with turbulence during tracking. Pyrex was chosen for its low expansion qualities so the mirror would not distort the images produced when it changed shape due to temperature variations. The mirror was cast in a mold with 36 raised mold blocks, the shape of a central hole was also part of the mold so light could pass through the finished mirror when it was used in a Cassegrain configuration. The defective mirror was used to test the annealing process, after the mold was re-engineered, a second mirror was successfully cast. After cooling several months, the mirror blank was transported by rail to Pasadena
18.
Saint-Gobain
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Saint-Gobain S. A. is a French multinational corporation, founded in 1665 in Paris and headquartered on the outskirts of Paris, at La Défense and in Courbevoie. Originally a mirror manufacturer, it now produces a variety of construction. The company is a component of the Euro Stoxx 50 stock market index, since the middle of the 17th century, luxury products such as silk textiles, lace and mirrors were in high demand. French minister of finance Jean-Baptiste Colbert wanted France to become completely self-sufficient in meeting domestic demand for luxury products, Colbert established by letters patent the public enterprise Manufacture royale de glaces de miroirs in October 1665. The company was created for a period of twenty years and would be financed in part by the State. The beneficiary and first director was the French financier Nicolas du Noyer, receiver of taxes of Orléans, the company had the informal name Compagnie du Noyer. To compete with the Italian mirror industry, Colbert commissioned several Venetian glassworkers he had enticed to Paris to work for the company, the first unblemished mirrors were produced in 1666. Soon the mirrors created in the Faubourg Saint-Antoine, under the French company, the French company was capable of producing mirrors that were 40 to 45 inches long, which at the time was considered impressive. Competition between France and the Venetians became so fierce that Venice considered it a crime for any glass artisan to leave and practice their trade elsewhere, especially in foreign territory. Nicolas du Noyer complained in writing that the jealous Venetians were unwilling to impart the secrets of glassmaking to the French workers, the distractions of Paris proved distracting to the workers, and supplies of firewood to stoke the furnaces were dearer in the capital than elsewhere. In 1678, the company produced the glass for the Hall of Mirrors at the Palace of Versailles, in 1683 the companys financial arrangement with the State was renewed for another two decades. However, in 1688 the rival Compagnie Thévart was created, also financed in part by the state, the two companies were in competition for seven years, until 1695, when the economy slowed down and their technical and commercial rivalry became counterproductive. Under an order from the French government, the two companies were forced to merge, creating the Compagnie Plastier, in 1702 Compagnie Plastier declared bankruptcy. A group of Franco-Swiss Protestant bankers rescued the company, changing the name to Compagnie Dagincourt. In 1789, as a consequence of the French Revolution, the state financial, the company now had to depend on the participation and capital of private investors, although it continued to remain partly under the control of the French state. In the 1820s, Saint-Gobain continued to function as it had under the Ancien Régime, manufacturing high-quality mirrors, however, in 1824, a new glass manufacturer was established in Commentry, France, and in 1837 several Belgian glass manufacturers were also founded. While Saint-Gobain continued to dominate the luxury high-quality mirror and glass markets, its newly created competitors focused their attention on making medium, the manufacture of products of such quality made mirrors and glass affordable for the masses. In response, the extended its product line to include lower-quality glass
19.
San Francisco
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San Francisco, officially the City and County of San Francisco, is the cultural, commercial, and financial center of Northern California. It is the birthplace of the United Nations, the California Gold Rush of 1849 brought rapid growth, making it the largest city on the West Coast at the time. San Francisco became a consolidated city-county in 1856, after three-quarters of the city was destroyed by the 1906 earthquake and fire, San Francisco was quickly rebuilt, hosting the Panama-Pacific International Exposition nine years later. In World War II, San Francisco was a port of embarkation for service members shipping out to the Pacific Theater. Politically, the city votes strongly along liberal Democratic Party lines, San Francisco is also the headquarters of five major banking institutions and various other companies such as Levi Strauss & Co. Dolby, Airbnb, Weebly, Pacific Gas and Electric Company, Yelp, Pinterest, Twitter, Uber, Lyft, Mozilla, Wikimedia Foundation, as of 2016, San Francisco is ranked high on world liveability rankings. The earliest archaeological evidence of habitation of the territory of the city of San Francisco dates to 3000 BC. Upon independence from Spain in 1821, the became part of Mexico. Under Mexican rule, the system gradually ended, and its lands became privatized. In 1835, Englishman William Richardson erected the first independent homestead, together with Alcalde Francisco de Haro, he laid out a street plan for the expanded settlement, and the town, named Yerba Buena, began to attract American settlers. Commodore John D. Sloat claimed California for the United States on July 7,1846, during the Mexican–American War, montgomery arrived to claim Yerba Buena two days later. Yerba Buena was renamed San Francisco on January 30 of the next year, despite its attractive location as a port and naval base, San Francisco was still a small settlement with inhospitable geography. The California Gold Rush brought a flood of treasure seekers, with their sourdough bread in tow, prospectors accumulated in San Francisco over rival Benicia, raising the population from 1,000 in 1848 to 25,000 by December 1849. The promise of fabulous riches was so strong that crews on arriving vessels deserted and rushed off to the gold fields, leaving behind a forest of masts in San Francisco harbor. Some of these approximately 500 abandoned ships were used at times as storeships, saloons and hotels, many were left to rot, by 1851 the harbor was extended out into the bay by wharves while buildings were erected on piles among the ships. By 1870 Yerba Buena Cove had been filled to create new land, buried ships are occasionally exposed when foundations are dug for new buildings. California was quickly granted statehood in 1850 and the U. S. military built Fort Point at the Golden Gate, silver discoveries, including the Comstock Lode in Nevada in 1859, further drove rapid population growth. With hordes of fortune seekers streaming through the city, lawlessness was common, and the Barbary Coast section of town gained notoriety as a haven for criminals, prostitution, entrepreneurs sought to capitalize on the wealth generated by the Gold Rush
20.
1906 San Francisco earthquake
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The 1906 San Francisco earthquake struck the coast of Northern California at 5,12 a. m. on April 18 with an estimated moment magnitude of 7.8 and a maximum Mercalli intensity of XI. Severe shaking was felt from Eureka on the North Coast to the Salinas Valley, devastating fires soon broke out in the city and lasted for several days. As a result, about 3,000 people died and over 80% of the city of San Francisco was destroyed, the events are remembered as one of the worst and deadliest natural disasters in the history of the United States. The death toll remains the greatest loss of life from a disaster in Californias history. The San Andreas Fault is a transform fault that forms part of the tectonic boundary between the Pacific Plate and the North American Plate. The strike-slip fault is characterized by mainly lateral motion in a dextral sense, the 1906 rupture propagated both northward and southward for a total of 296 miles. This fault runs the length of California from the Salton Sea in the south to Cape Mendocino in the north, the maximum observed surface displacement was about 20 feet, geodetic measurements show displacements of up to 28 feet. The 1906 earthquake preceded the development of the Richter magnitude scale by three decades. The most widely accepted estimate for the magnitude of the quake on the moment magnitude scale is 7.8. According to findings published in the Journal of Geophysical Research, severe deformations in the earths crust took place both before and after the earthquakes impact. Accumulated strain on the faults in the system was relieved during the earthquake, the main shock epicenter occurred offshore about 2 miles from the city, near Mussel Rock. Shaking was felt from Oregon to Los Angeles, and inland as far as central Nevada, a strong foreshock preceded the main shock by about 20 to 25 seconds. The strong shaking of the main shock lasted about 42 seconds, there were decades of minor earthquakes – more than at any other time in the historical record for northern California – before the 1906 quake. For years, the epicenter of the quake was assumed to be near the town of Olema, in the Point Reyes area of Marin County, because of evidence of the degree of local earth displacement. In the 1960s, a seismologist at UC Berkeley proposed that the epicenter was more likely offshore of San Francisco, at the time,375 deaths were reported, partly because hundreds of fatalities in Chinatown went ignored and unrecorded. The total number of deaths is uncertain today, and is estimated to be roughly 3,000 at minimum. Most of the deaths occurred in San Francisco itself, but 189 were reported elsewhere in the Bay Area, nearby cities, such as Santa Rosa and San Jose, in Monterey County, the earthquake permanently shifted the course of the Salinas River near its mouth. Where previously the river emptied into Monterey Bay between Moss Landing and Watsonville, it was diverted 6 miles south to a new channel just north of Marina
21.
First light (astronomy)
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In astronomy, first light is the first use of a telescope to take an astronomical image after it has been constructed. This is often not the first viewing using the telescope, optical tests will probably have been performed during daylight to adjust the components. The first light image is normally of little scientific interest and is of poor quality since the various elements are yet to be adjusted for optimum efficiency. A well-known and spectacular astronomical object is chosen as a subject. For example, the 5. 08-metre Hale Telescope saw first light January 26,1949, the image was published in many magazines and is available on Caltech Archives. The Isaac Newton Telescope had two first lights, one in England in 1965 with its mirror, and another in 1984 at La Palma island. The second first light was done with a camera that showed the Crab Pulsar flashing. The Large Binocular Telescope had its first light with a primary mirror on October 12,2005. The second primary mirror was installed in January 2006 and became operational in January 2008. The 10.4 m Gran Telescopio Canarias had a first light image of Tycho 1205081 on 14 July 2007, the IRIS solar space observatory achieved first light on July 17,2013. The PI noted, The quality of images and spectra we are receiving from IRIS is amazing and this is just what we were hoping for
22.
Leviathan of Parsonstown
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Leviathan of Parsonstown is the unofficial name of the Rosse six-foot telescope. This is a reflecting telescope of 72 in aperture, which was the largest telescope in the world from 1845 until the construction of the 100-inch Hooker Telescope in 1917. The Rosse six-foot telescope was built by William Parsons, 3rd Earl of Rosse on his estate, Birr Castle, Parsons improved the techniques of casting, grinding and polishing large telescope mirrors from speculum metal, and constructed steam-powered grinding machines for parabolic mirrors. His 3 ft mirror of 1839 was cast in pieces, fitted together before grinding and polishing. In 1842, Parsons cast his first 6 ft mirror, but it took another five casts, speculum mirrors tarnished rapidly, with two mirrors, one could be used in the telescope while the other was being re-polished. The telescope tube and supporting structure were completed in 1845, the mirror was 5 in thick and weighed almost 3 tons. This required a mirror cell to support and to prevent the mirror deforming under its own weight, the length of the tube and mirror box is about 54 ft, including the mirror it weighed about 12 tons. The azimuth range is limited to one hour by the supporting walls that flank the tube on its eastern and western sides. The walls are 23 ft apart,40 ft high, and 71 ft long, a chain and counterweight keeps the telescope in balance, another chain with a winch controls the altitude. A rack and pinion beam underneath the tube controls the azimuth and this beam is connected to the eastern supporting wall, where it can move on a circular iron arc to allow the telescope to change altitude. The tube is of the Newtonian design with the eyepiece on its western side, at low altitude, the observer accesses the eyepiece from a wooden gallery that spans the distance between the walls and can slide up and down guides to follow the telescope in altitude. A cage on the gallery moves sideways to reach the eyepiece at different azimuth, at high elevation, curved galleries on top of the western wall are used, which can be moved across the wall to follow the telescope in azimuth. The purpose of the telescope was to re-visit the nebulae in the catalogues of Charles Messier and these catalogues list star clusters as well as nebulae, and the question was whether the latter were merely unresolved star clusters or genuinely nebulous regions of space. If resolved into stars they might be the first galaxies to be identified as such, Parsons discovered that several nebulae had a spiral structure, suggesting dynamical laws. The most notable spiral nebula observed by Parsons was Messier 51, after William Parsons died in 1867, the 4th Earl continued to operate the six-foot telescope. From 1874 to 1878, J. L. E. Dreyer worked with the telescope and began the compilation of his New General Catalogue of Nebulae, although the 4th Earl built a smaller 3 ft equatorial in 1876, the six-foot telescope remained in use until about 1890. After his death in 1908, the telescope was partly dismantled, the tube, second mirror box, and universal joint survived. Following a TV programme, lecture, and book by Patrick Moore, there was renewed interest in the telescope in the 1970s
23.
Newtonian telescope
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The Newtonian telescope is a type of reflecting telescope invented by the British scientist Sir Isaac Newton, using a concave primary mirror and a flat diagonal secondary mirror. Newton’s first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope, the Newtonian telescopes simple design makes it very popular with amateur telescope makers. Newtons idea for a telescope was not new. Newton may even have read James Gregorys 1663 book Optica Promota which described reflecting telescope designs using parabolic mirrors, Newton built his reflecting telescope because he suspected it could prove his theory that white light is composed of a spectrum of colours. Colour distortion was the fault of refracting telescopes of Newtons day. If this were true, then chromatic aberration could be eliminated by building a telescope which did not use a lens – a reflecting telescope, in late 1668 Isaac Newton built his first reflecting telescope. He chose an alloy of tin and copper as the most suitable material for his objective mirror and he later devised means for shaping and grinding the mirror and may have been the first to use a pitch lap to polish the optical surface. He chose a shape for his mirror instead of a parabola to simplify construction, even though it would introduce spherical aberration. This unique addition allowed the image to be viewed with minimal obstruction of the objective mirror and he also made the tube, mount, and fittings. Newtons first version had a mirror diameter of 1.3 inches. He found that the telescope worked without colour distortion and that he could see the four Galilean moons of Jupiter, Newtons friend Isaac Barrow showed a second telescope to a small group from the Royal Society of London at the end of 1671. They were so impressed with it that they demonstrated it to Charles II in January 1672, Newton was admitted as a fellow of the society in the same year. Like Gregory before him, Newton found it hard to construct an effective reflector and it was difficult to grind the speculum metal to a regular curvature. The surface also tarnished rapidly, the consequent low reflectivity of the mirror, because of these difficulties in construction, the Newtonian reflecting telescope was initially not widely adopted. In 1721 John Hadley showed a model to the Royal Society. Hadley had solved many of the problems of making a parabolic mirror and his Newtonian with a mirror diameter of 6 inches compared favourably with the large aerial refracting telescopes of the day. The size of reflecting telescopes subsequently grew rapidly, with designs doubling in primary mirror diameter about every 50 years and they are free of chromatic aberration found in refracting telescopes. Newtonian telescopes are usually less expensive for any given objective diameter than comparable quality telescopes of other types, since there is only one surface that needs to be ground and polished into a complex shape, overall fabrication is much simpler than other telescope designs
24.
Cassegrain reflector
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The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas. Alternatively, as in radio telescopes, the final focus may be in front of the primary. In an asymmetrical Cassegrain, the mirror may be tilted to avoid obscuration of the primary or to avoid the need for a hole in the primary mirror, the classic Cassegrain configuration uses a parabolic reflector as the primary while the secondary mirror is hyperbolic. Modern variants often have a primary for increased performance, or the primary and/or secondary are spherical or elliptical for ease of manufacturing. The Cassegrain reflector is named after a published reflecting telescope design that appeared in the April 25,1672 Journal des sçavans which has been attributed to Laurent Cassegrain. Similar designs using convex secondaries have been found in the Bonaventura Cavalieris 1632 writings describing burning mirrors, james Gregorys 1662 attempts to create a reflecting telescope included a Cassegrain configuration, judging by a convex secondary mirror found among his experiments. The Cassegrain design is used in catadioptric systems. The Classic Cassegrain has a primary mirror, and a hyperbolic secondary mirror that reflects the light back down through a hole in the primary. Folding the optics makes this a compact design, on smaller telescopes, and camera lenses, the secondary is often mounted on an optically flat, optically clear glass plate that closes the telescope tube. This support eliminates the diffraction effects caused by a straight-vaned support spider. The closed tube stays clean, and the primary is protected and it makes use of the special properties of parabolic and hyperbolic reflectors. A concave parabolic reflector will reflect all incoming light rays parallel to its axis of symmetry to a single point, a convex hyperbolic reflector has two foci and will reflect all light rays directed at one of its two foci towards its other focus. The parabolic mirror reflects parallel light rays entering the telescope to its focus, the hyperbolic mirror then reflects those light rays to its other focus, where the image is observed. The Ritchey-Chrétien is a specialized Cassegrain reflector which has two hyperbolic mirrors and it is free of coma and spherical aberration at a flat focal plane, making it well suited for wide field and photographic observations. It was invented by George Willis Ritchey and Henri Chrétien in the early 1910s and this design is very common in large professional research telescopes, including the Hubble Space Telescope, Keck Telescopes and VLT telescope, it is also found in high-grade amateur telescopes. Ingalls, the astronomy editor at the time. It uses a concave primary mirror and a convex spherical secondary. While this system is easier to polish than a classic Cassegrain or Ritchey-Chretien system, because this is less noticeable at longer focal ratios, Dall-Kirkhams are seldom faster than f/15
25.
Reflecting telescope
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A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the telescope which. Although reflecting telescopes produce other types of aberrations, it is a design that allows for very large diameter objectives. Almost all of the telescopes used in astronomy research are reflectors. Reflecting telescopes come in many variations and may employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is referred to as a catoptric telescope. The idea that curved mirrors behave like lenses dates back at least to Alhazens 11th century treatise on optics, the potential advantages of using parabolic mirrors, primarily reduction of spherical aberration with no chromatic aberration, led to many proposed designs for reflecting telescopes. The most notable being James Gregory, who published a design for a ‘reflecting’ telescope in 1663. It would be ten years, before the experimental scientist Robert Hooke was able to build this type of telescope, Isaac Newton has been generally credited with building the first reflecting telescope in 1668. It used a spherically ground metal primary mirror and a diagonal mirror in an optical configuration that has come to be known as the Newtonian telescope. A curved primary mirror is the reflector telescopes basic optical element that creates an image at the focal plane, the distance from the mirror to the focal plane is called the focal length. The primary mirror in most modern telescopes is composed of a glass cylinder whose front surface has been ground to a spherical or parabolic shape. A thin layer of aluminum is deposited onto the mirror. Some telescopes use primary mirrors which are made differently, molten glass is rotated to make its surface paraboloidal, and is kept rotating while it cools and solidifies. The resulting mirror shape approximates a desired paraboloid shape that requires grinding and polishing to reach the exact figure needed. Reflecting telescopes, just like any other system, do not produce perfect images. The use of mirrors avoids chromatic aberration but they produce other types of aberrations, to avoid this problem most reflecting telescopes use parabolic shaped mirrors, a shape that can focus all the light to a common focus. Field curvature - The best image plane is in general curved and it is sometimes corrected by a field flattening lens
26.
Spectroscopy
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Spectroscopy /spɛkˈtrɒskəpi/ is the study of the interaction between matter and electromagnetic radiation. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, later the concept was expanded greatly to include any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency. Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers, daily observations of color can be related to spectroscopy. Neon lighting is an application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies, neon lamps use collision of electrons with the gas to excite these emissions. Inks, dyes and paints include chemical compounds selected for their characteristics in order to generate specific colors. A commonly encountered molecular spectrum is that of nitrogen dioxide, gaseous nitrogen dioxide has a characteristic red absorption feature, and this gives air polluted with nitrogen dioxide a reddish-brown color. Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the color of the sky, Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect, identify and quantify information about the atoms, Spectroscopy is also used in astronomy and remote sensing on earth. The measured spectra are used to determine the composition and physical properties of astronomical objects. One of the concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums, mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency and this plot is one type of spectrum, with the peak often referred to as a spectral line, and most spectral lines have a similar appearance. In quantum mechanical systems, the resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the matches the energy difference between the two states. The energy of a photon is related to its frequency by E = h ν where h is Plancks constant, spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states
27.
Parallax
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The term is derived from the Greek word παράλλαξις, meaning alternation. Due to foreshortening, nearby objects have a larger parallax than more distant objects when observed from different positions, astronomers use the principle of parallax to measure distances to the closer stars. Here, the parallax is the semi-angle of inclination between two sight-lines to the star, as observed when the Earth is on opposite sides of the Sun in its orbit. Parallax also affects optical instruments such as rifle scopes, binoculars, microscopes, many animals, including humans, have two eyes with overlapping visual fields that use parallax to gain depth perception, this process is known as stereopsis. In computer vision the effect is used for stereo vision, and there is a device called a parallax rangefinder that uses it to find range. A simple everyday example of parallax can be seen in the dashboard of motor vehicles that use a needle-style speedometer gauge. When viewed from directly in front, the speed may show exactly 60, as the eyes of humans and other animals are in different positions on the head, they present different views simultaneously. This is the basis of stereopsis, the process by which the brain exploits the parallax due to the different views from the eye to gain depth perception, animals also use motion parallax, in which the animals move to gain different viewpoints. For example, pigeons bob their heads up and down to see depth, the motion parallax is exploited also in wiggle stereoscopy, computer graphics which provide depth cues through viewpoint-shifting animation rather than through binocular vision. Parallax arises due to change in viewpoint occurring due to motion of the observer, of the observed, what is essential is relative motion. By observing parallax, measuring angles, and using geometry, one can determine distance, astronomers also use the word parallax as a synonym for distance measurent by other methods, see parallax #Astronomy. In a geostatic model, the movement of the star would have to be taken as real with the star oscillating across the sky with respect to the background stars, the parsec is defined as the distance for which the annual parallax is 1 arcsecond. Annual parallax is measured by observing the position of a star at different times of the year as the Earth moves through its orbit. Measurement of annual parallax was the first reliable way to determine the distances to the closest stars, the first successful measurements of stellar parallax were made by Friedrich Bessel in 1838 for the star 61 Cygni using a heliometer. Stellar parallax remains the standard for calibrating other measurement methods, accurate calculations of distance based on stellar parallax require a measurement of the distance from the Earth to the Sun, now based on radar reflection off the surfaces of planets. The angles involved in these calculations are very small and thus difficult to measure, the nearest star to the Sun, Proxima Centauri, has a parallax of 0.7687 ±0.0003 arcsec. This angle is approximately that subtended by an object 2 centimeters in diameter located 5.3 kilometers away, the fact that stellar parallax was so small that it was unobservable at the time was used as the main scientific argument against heliocentrism during the early modern age. In 1989, the satellite Hipparcos was launched primarily for obtaining improved parallaxes and proper motions for over 100,000 nearby stars, increasing the reach of the method tenfold
28.
Nebula
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A nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, nebula was a name for any diffuse astronomical object, the Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others. Most nebulae are of vast size, even millions of years in diameter. The Orion Nebula, the brightest nebula in the sky that occupies a region twice the diameter of the full Moon, can be viewed with the naked eye but was missed by early astronomers. Many nebulae are visible due to their fluorescence caused by the hot stars, while others are so diffuse they can only be detected with long exposures. Some nebulae are variably illuminated by T Tauri variable stars, Nebulae are often star-forming regions, such as in the Pillars of Creation in the Eagle Nebula. In these regions the formations of gas, dust, and other materials together to form denser regions, which attract further matter. The remaining material is believed to form planets and other planetary system objects. Around 150 AD, Claudius Ptolemaeus recorded, in books VII–VIII of his Almagest and he also noted a region of nebulosity between the constellations Ursa Major and Leo that was not associated with any star. The first true nebula, as distinct from a cluster, was mentioned by the Persian astronomer Abd al-Rahman al-Sufi. He noted a little cloud where the Andromeda Galaxy is located and he also cataloged the Omicron Velorum star cluster as a nebulous star and other nebulous objects, such as Brocchis Cluster. The supernova that created the Crab Nebula, the SN1054, was observed by Arabic, in 1610, Nicolas-Claude Fabri de Peiresc discovered the Orion Nebula using a telescope. This nebula was observed by Johann Baptist Cysat in 1618. However, the first detailed study of the Orion Nebula was not performed until 1659 by Christiaan Huygens, in 1715, Edmund Halley published a list of six nebulae. This number steadily increased during the century, with Jean-Philippe de Cheseaux compiling a list of 20 in 1746, from 1751 to 1753, Nicolas Louis de Lacaille cataloged 42 nebulae from the Cape of Good Hope, most of which were previously unknown. Charles Messier then compiled a catalog of 103 nebulae by 1781, his interest was detecting comets, the number of nebulae was then greatly expanded by the efforts of William Herschel and his sister Caroline Herschel. Their Catalogue of One Thousand New Nebulae and Clusters of Stars was published in 1786, a second catalog of a thousand was published in 1789 and the third and final catalog of 510 appeared in 1802. During much of their work, William Herschel believed that these nebulae were merely unresolved clusters of stars, in 1790, however, he discovered a star surrounded by nebulosity and concluded that this was a true nebulosity, rather than a more distant cluster
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Adaptive optics
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Adaptive optics works by measuring the distortions in a wavefront and compensating for them with a device that corrects those errors such as a deformable mirror or a liquid crystal array. Adaptive optics should not be confused with active optics, which works on a timescale to correct the primary mirror geometry. Adaptive optics was first envisioned by Horace W, some of the initial development work on adaptive optics was done by the US military during the Cold War and was intended for use in tracking Soviet satellites. The simplest form of adaptive optics is tip-tilt correction, which corresponds to correction of the tilts of the wavefront in two dimensions and this is performed using a rapidly moving tip–tilt mirror that makes small rotations around two of its axes. A significant fraction of the aberration introduced by the atmosphere can be removed in this way, tip–tilt mirrors are effectively segmented mirrors having only one segment which can tip and tilt, rather than having an array of multiple segments that can tip and tilt independently. Due to the simplicity of such mirrors and having a large stroke, meaning they have large correcting power, most AO systems use these, first. Higher order aberrations may then be corrected with deformable mirrors, when light from a star or another astronomical object enters the Earths atmosphere, atmospheric turbulence can distort and move the image in various ways. Visual images produced by any larger than approximately 20 centimeters are blurred by these distortions. In order to perform adaptive optics correction, the shape of the incoming wavefronts must be measured as a function of position in the aperture plane. The mean wavefront perturbation in each pixel is calculated and this pixelated map of the wavefronts is fed into the deformable mirror and used to correct the wavefront errors introduced by the atmosphere. The deformable mirror corrects incoming light so that the images appear sharp, because a science target is often too faint to be used as a reference star for measuring the shape of the optical wavefronts, a nearby brighter guide star can be used instead. This severely limits the application of the technique for astronomical observations, another major limitation is the small field of view over which the adaptive optics correction is good. As the angular distance from the star increases, the image quality degrades. A technique known as adaptive optics uses several deformable mirrors to achieve a greater field of view. An alternative is the use of a beam to generate a reference light source in the atmosphere. LGSs come in two flavors, Rayleigh guide stars and sodium guide stars, Rayleigh guide stars work by propagating a laser, usually at near ultraviolet wavelengths, and detecting the backscatter from air at altitudes between 15–25 km. Sodium guide stars use laser light at 589 nm to excite sodium atoms higher in the mesosphere and thermosphere, which then appear to glow. The LGS can then be used as a wavefront reference in the way as a natural guide star – except that natural reference stars are still required for image position information
30.
DARPA
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The Defense Advanced Research Projects Agency is an agency of the U. S. Department of Defense responsible for the development of emerging technologies for use by the military. DARPA was created in February 1958 as the Advanced Research Projects Agency by President Dwight D. Eisenhower and its purpose was to formulate and execute research and development projects to expand the frontiers of technology and science, with the aim to reach beyond immediate military requirements. DARPA was created in response to the Soviet launching of Sputnik 1 in 1957, the name of the organization changed several times from its founding name ARPA, DARPA, ARPA, and DARPA. DARPA is independent from other research and development and reports directly to senior Department of Defense management. DARPA has about 240 employees, of whom 13 are in management, dARPA-funded projects have provided significant technologies that influenced many non-military fields, such as computer networking and graphical user interfaces in information technology. S. The mission statement has evolved over time, today, DARPAs mission is still to prevent technological surprise to the U. S. but also to create technological surprise for U. S. enemies. The creation of the Advanced Research Projects Agency was authorized by President Dwight D.15 and its creation was directly attributed to the launching of Sputnik and to U. S. realization that the Soviet Union had developed the capacity to rapidly exploit military technology. Initial funding of ARPA was $520 million, ARPAs first director, Roy Johnson, left a $160,000 management job at General Electric for an $18,000 job at ARPA. Herbert York from Lawrence Livermore National Laboratory was hired as his scientific assistant, Johnson and York were both keen on space projects, but when NASA was established later in 1958 all space projects and most of ARPAs funding were transferred to it. Johnson resigned and ARPA was repurposed to do high-risk, high-gain, far out basic research, ARPAs second director was Brigadier General Austin W. Betts, who resigned in early 1961. He was succeeded by Jack Ruina who served until 1963, Ruina, the first scientist to administer ARPA, managed to raise its budget to $250 million. In pursuit of this mission, DARPA has developed and transferred technology programs encompassing a range of scientific disciplines that address the full spectrum of national security needs. From 1958 to 1965, ARPAs emphasis centered on major issues, including space, ballistic missile defense. During 1960, all of its civilian space programs were transferred to the National Aeronautics and Space Administration and the military space programs to the individual Services. This allowed ARPA to concentrate its efforts on the Project Defender, Project Vela, and Project AGILE Programs, and to work on computer processing, behavioral sciences. The DEFENDER and AGILE Programs formed the foundation of DARPA sensor, surveillance, and directed energy R&D, particularly in the study of radar, infrared sensing, ARPA at this point played an early role in Transit a predecessor to the Global Positioning System. Fast-forward to 1959 when a joint effort between DARPA and the Johns Hopkins Applied Physics Laboratory began to fine-tune the early explorers’ discoveries, TRANSIT, sponsored by the Navy and developed under the leadership of Dr. Richard Kirschner at Johns Hopkins, was the first satellite positioning system. The agency was renamed the Defense Advanced Research Projects Agency in 1972, and during the early 1970s, it emphasized direct energy programs, information processing, concerning information processing, DARPA made great progress, initially through its support of the development of time-sharing
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Strategic Defense Initiative
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The Strategic Defense Initiative was a proposed missile defense system intended to protect the United States from attack by ballistic strategic nuclear weapons. The system, which was to combine ground-based units and orbital deployment platforms, was first publicly announced by President Ronald Reagan on March 23,1983, the initiative focused on strategic defense rather than the prior strategic offense doctrine of mutual assured destruction. The Strategic Defense Initiative Organization was set up in 1984 within the United States Department of Defense to oversee the Strategic Defense Initiative, Reagan was a vocal critic of MAD doctrine. The ambitious initiative was criticized for threatening to destabilize the MAD-approach. SDI was nicknamed largely in the media as Star Wars. Under the SDIOs Innovative Sciences and Technology Office, headed by physicist and it was never truly developed or deployed, though certain aspects of SDI research and technologies paved the way for some anti-ballistic missile systems of today. BMDO was renamed to the Missile Defense Agency in 2002 and this article covers defense efforts under the SDIO. Today, the United States holds a significant advantage in the field of advanced missile defense systems through years of extensive research. The US and the UK also have both laser weapons and 360 degree laser shields in development, which are expected to be ready for use as early as 2020. Many of the obtained technological insights were transferred to subsequent programs, George Shultz, Secretary of State under Reagan, suggests that a 1967 lecture by physicist Edward Teller was an important precursor to SDI. In the lecture Teller talked about the idea of defending against nuclear missiles by using nuclear weapons, held at Lawrence Livermore National Laboratory, the lecture was attended by Reagan shortly after he became the governor of California. However, he was struck by their comments that while they could track the attack down to the individual targets, Shultz suggests that this feeling of helplessness, coupled with the defensive ideas proposed by Teller a decade earlier, combined to form the impetus of the SDI. It was designed to replace the doctrine of Mutual assured destruction, O Group was headed by physicist Lowell Wood, a protégé and friend of Edward Teller. Ronald Reagan was told of Hagelsteins breakthrough by Teller in 1983, the concept for the space-based portion was to use lasers to shoot down incoming Soviet intercontinental ballistic missiles armed with nuclear warheads. Although Nazi Germany put considerable effort into the first surface-to-air missiles after 1943 and their research proved valuable to teams in the US and Soviet Union, where missile programs slowly developed in the immediate post-war era. As the Cold War started, the Soviets found themselves facing massive USAF, in response they dramatically increased their efforts in SAM development, deploying the S-25 Berkut system around Moscow as early as 1955. This was followed by the improved and semi-mobile S-75 Dvina. Similar US and UK weapons soon followed, by the late 1950s, as missiles developed both in quality and number, the ability for the US air fleet to penetrate Soviet airspace was increasingly at risk
32.
National Science Foundation
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The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health, with an annual budget of about US$7.0 billion, the NSF funds approximately 24% of all federally supported basic research conducted by the United States colleges and universities. In some fields, such as mathematics, computer science, economics, and the social sciences, the current NSF director, confirmed in March 2014, is astronomer France A. Córdova, former president of Purdue University. The NSF seeks to fulfill its mission chiefly by issuing competitive, the NSF also makes some contracts. Some proposals are solicited, and some are not, the NSF funds both kinds, the NSF does not operate its own laboratories, unlike other federal research agencies, notable examples being the NASA and the National Institutes of Health. The NSF receives over 50,000 such proposals each year and those funded are typically projects that are ranked highest in a merit review process, the current version of which was introduced in 1997. For example, reviewers cannot work at the NSF itself, nor for the institution that employs the proposing researchers, all proposal evaluations are confidential, the proposing researchers may see them, but they do not see the names of the reviewers. However, both already had been mandated for all NSF merit review procedures in the 2010 re-authorization of the America COMPETES Act. The Act also includes an emphasis on promoting potentially transformative research, most NSF grants go to individuals or small groups of investigators, who carry out research at their home campuses. Other grants provide funding for research centers, instruments. Still, others fund national-scale facilities that are shared by the community as a whole. In addition to researchers and research facilities, NSF grants also support science, engineering, Undergraduates can receive funding through Research Experiences for Undergraduates summer programs. K-12 and some community college instructors are eligible to participate in compensated Research Experiences for Teachers programs, the NSFs workforce numbers about 1,700, nearly all working at its Arlington headquarters. In June 2013 it was announced that the NSF would relocate its headquarters to Alexandria, Virginia in 2017. S, examples include initiatives in, Nanotechnology The science of learning Digital libraries The ecology of infectious diseases The NSF was established by the National Science Foundation Act of 1950. Its stated mission is To promote the progress of science, to advance the health, prosperity, and welfare. Some historians of science have argued that the result was a compromise between too many clashing visions of the purpose and scope of the federal government. The NSF was certainly not the government agency for the funding of basic science. By 1950, support for areas of research had already become dominated by specialized agencies such as the National Institutes of Health
33.
Observational astronomy
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It is the practice of observing celestial objects by using telescopes and other astronomical apparatus. 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 partly compensated by the fact that astronomers have a vast number of visible examples of stellar phenomena that can be examined. This allows for data to be plotted on graphs. Nearby examples of phenomena, such as variable stars, can then be used to infer the behavior of more distant representatives. Those distant yardsticks can then be employed to measure other phenomena in that neighborhood, galileo Galilei turned a telescope to the heavens and recorded what he saw. Since that time, observational astronomy has made steady advances with each improvement in telescope technology, visible-light astronomy falls in the middle of this range. Infrared astronomy deals with the detection and 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 wavelengths where the atmosphere is opaque. Radio astronomy detects radiation of millimetre to decametre wavelength, the receivers are similar to those used in radio broadcast transmission but much more sensitive. High-energy astronomy includes X-ray astronomy, gamma-ray astronomy, and extreme UV astronomy, in addition to using electromagnetic radiation, modern astrophysicists can also 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 relatively transparent at the wavelengths being detected. Observatories are usually located at high altitudes so as to minimise the absorption and distortion caused by the Earths atmosphere, some wavelengths of infrared light are heavily absorbed by water vapor, so many infrared observatories are located in dry places at high altitude, or in space. Powerful gamma rays can, however be detected by the air showers they produce. For much of the history of astronomy, almost all observation was performed in the visual spectrum with optical telescopes. The seeing conditions depend on the turbulence and thermal variations in the air, locations that are frequently cloudy or suffer from atmospheric turbulence limit the resolution of observations. Likewise the presence of the full Moon can brighten up the sky with scattered light, 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 number of cloudless days
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Edwin Hubble
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Edwin Powell Hubble was an American astronomer. He played a role in establishing the fields of extragalactic astronomy. Hubbles Law implies that the universe is expanding, Hubble also discovered that many objects previously thought to be clouds of dust and gas and classified as nebulae were actually galaxies beyond the Milky Way. A decade before, the American astronomer Vesto Slipher had provided the first evidence that the light from many of these nebulae was strongly red-shifted, indicative of high recession velocities. Hubbles name is most widely recognized for the Hubble Space Telescope which was named in his honor, with a prominently displayed in his hometown of Marshfield. Edwin Hubble was born to Virginia Lee Hubble and John Powell Hubble, an executive, in Marshfield, Missouri. In his younger days, he was noted more for his athletic prowess than his intellectual abilities, Edwin was a gifted athlete playing baseball, football, basketball, and he ran track in both high school and college. He played a variety of positions on the court from center to shooting guard. In fact Hubble even led the University of Chicagos basketball team to their first conference title in 1907 and he won seven first places and a third place in a single high school track and field meet in 1906. His studies at the University of Chicago were concentrated on law, Hubble also became a member of the Kappa Sigma Fraternity. In 1909, Hubbles father moved his family from Chicago to Shelbyville, Kentucky, so that the family could live in a small town, the family moved once more to Everett Avenue, in Louisvilles Highlands neighborhood, to accommodate Edwin and William. After the death of his father in 1913, Edwin returned to the Midwest from Oxford, instead, he proceeded to teach Spanish, physics and mathematics at New Albany High School in New Albany, Indiana, where he also coached the boys basketball team. His dissertation was titled Photographic Investigations of Faint Nebulae, after the United States declared war on Germany in 1917, Hubble rushed to complete his PhD dissertation so he could join the military. Hubble volunteered for the United States Army and was assigned to the newly created 86th Division and he rose to the rank of lieutenant colonel, and was found fit for overseas duty on July 9,1918, but the 86th Division never saw combat. After the end of World War I, Hubble spent a year in Cambridge, in 1919, Hubble was offered a staff position at the Carnegie Institutions Mount Wilson Observatory, near Pasadena, California, by George Ellery Hale, the founder and director of the observatory. Hubble remained on staff at Mount Wilson until his death in 1953, shortly before his death, Hubble became the first astronomer to use the newly completed giant 200-inch reflector Hale Telescope at the Palomar Observatory near San Diego, California. Hubble also worked as a civilian for U. S, the results of his studies were credited with greatly improving design, performance, and military effectiveness of bombs and rockets. For his work there, he received the Legion of Merit award, although Hubble was raised as a Christian, he later became an agnostic
35.
Spiral galaxy
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A spiral galaxy is a type of galaxy originally described by Edwin Hubble in his 1936 work The Realm of the Nebulae and, as such, forms part of the Hubble sequence. Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and these are surrounded by a much fainter halo of stars, many of which reside in globular clusters. Spiral galaxies are named for the structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the surrounding disc because of the young, hot OB stars that inhabit them. Roughly two-thirds of all spirals are observed to have a component in the form of a bar-like structure, extending from the central bulge. Our own Milky Way has recently confirmed to be a barred spiral. The most convincing evidence for its existence comes from a recent survey, performed by the Spitzer Space Telescope, together with irregular galaxies, spiral galaxies make up approximately 60% of galaxies in the local Universe. They are mostly found in low-density regions and are rare in the centers of galaxy clusters, Spiral arms are regions of stars that extend from the center of spiral and barred spiral galaxies. These long, thin regions resemble a spiral and thus give spiral galaxies their name, naturally, different classifications of spiral galaxies have distinct arm-structures. Sc and SBc galaxies, for instance, have very loose arms, whereas Sa, either way, spiral arms contain many young, blue stars, which make the arms so bright. A bulge is a huge, tightly packed group of stars, the term commonly refers to the central group of stars found in most spiral galaxies. Using the Hubble classification, the bulge of Sa galaxies is usually composed of Population II stars, further, the bulge of Sa and SBa galaxies tends to be large. In contrast, the bulges of Sc and SBc galaxies are much smaller and are composed of young, some bulges have similar properties to those of elliptical galaxies, others simply appear as higher density centers of disks, with properties similar to disk galaxies. Many bulges are thought to host a supermassive black hole at their centers, such black holes have never been directly observed, but many indirect proofs exist. In our own galaxy, for instance, the object called Sagittarius A* is believed to be a black hole. There is a correlation between the mass of the black hole and the velocity dispersion of the stars in the bulge. However, some stars inhabit a spheroidal halo or galactic spheroid, the orbital behaviour of these stars is disputed, but they may describe retrograde and/or highly inclined orbits, or not move in regular orbits at all. The galactic halo also contains many globular clusters, due to their irregular movement around the center of the galaxy—if they do so at all—these stars often display unusually high proper motion
36.
Andromeda Galaxy
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The Andromeda Galaxy, also known as Messier 31, M31, or NGC224, is a spiral galaxy approximately 780 kiloparsecs from Earth. It is the nearest major galaxy to the Milky Way and was referred to as the Great Andromeda Nebula in older texts. It received its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda. Andromeda is approximately 220,000 light years across, and it is the largest galaxy of the Local Group, which contains the Milky Way, the Triangulum Galaxy. The mass of the Andromeda Galaxy is estimated to be 1. 5×1012 solar masses, the Milky Way and Andromeda galaxies are expected to collide in 4.5 billion years, eventually merging to form a giant elliptical galaxy or perhaps a large disc galaxy. Around the year 964, the Persian astronomer Abd al-Rahman al-Sufi described the Andromeda Galaxy, star charts of that period labeled it as the Little Cloud. In 1612, the German astronomer Simon Marius gave a description of the Andromeda Galaxy based on telescopic observations. In 1764, Charles Messier catalogued Andromeda as object M31 and incorrectly credited Marius as the discoverer despite it being visible to the naked eye, in 1785, the astronomer William Herschel noted a faint reddish hue in the core region of Andromeda. In 1850, William Parsons, 3rd Earl of Rosse, saw, in 1864, William Huggins noted that the spectrum of Andromeda differs from a gaseous nebula. The spectra of Andromeda displays a continuum of frequencies, superimposed with dark lines that help identify the chemical composition of an object. Andromedas spectrum is similar to the spectra of individual stars. In 1885, a supernova was seen in Andromeda, the first, at the time Andromeda was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, and was named accordingly, Nova 1885. In 1887, Isaac Roberts took the first photographs of Andromeda, Roberts actually mistook Andromeda and similar spiral nebulae as solar systems being formed. In 1912, Vesto Slipher used spectroscopy to measure the velocity of Andromeda with respect to our solar system—the largest velocity yet measured. In 1917, Heber Curtis observed a nova within Andromeda, searching the photographic record,11 more novae were discovered. Curtis noticed that these novae were, on average,10 magnitudes fainter than those that occurred elsewhere in the sky, as a result, he was able to come up with a distance estimate of 500,000 light-years. He became a proponent of the island universes hypothesis, which held that spiral nebulae were actually independent galaxies. In 1920, the Great Debate between Harlow Shapley and Curtis took place, concerning the nature of the Milky Way, spiral nebulae, in 1922 Ernst Öpik presented a method to estimate the distance of Andromeda using the measured velocities of its stars
37.
Fritz Zwicky
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Fritz Zwicky was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, in 1933, Zwicky was the first to use the virial theorem to infer the existence of unseen dark matter, describing it as dunkle Materie. Fritz Zwicky was born in Varna, in the Principality of Bulgaria and his father, Fridolin, was a prominent industrialist in the Bulgarian city and also served as ambassador of Norway in Varna. The Zwicky House in Varna was designed and built by Fridolin Zwicky, fritzs mother, Franziska Vrček, was an ethnic Czech of the Austro-Hungarian Empire. Fritz was the oldest of the Zwicky familys three children, he had a brother named Rudolf and a sister, Leonie. Fritzs mother died in Varna in 1927, and his father Fridolin remained in Bulgaria until 1945 and his sister Leonie married a Bulgarian from Varna and spent her entire life in the city. In 1904, at the age of six, Fritz was sent to his grandparents in the familys ancestral canton in Glarus, Switzerland, to study commerce. His interests shifted to math and physics and he received an education in mathematics and experimental physics at the Swiss Federal Polytechnic, located in Zurich. He was responsible for positing numerous cosmological theories that have a impact on the understanding of our universe today. He was the first to coin the term supernova during his fostering the concept of neutron stars, Zwicky was a lone wolf and did all of his own mathematical work. He intended to write an autobiography titled, Operation Lone Wolf and it would be five years later when Oppenheimer would publish his landmark paper announcing neutron stars. He developed some of the earliest jet engines and holds over 50 patents, many in jet propulsion, and is the inventor of the Underwater Jet, the Two Piece Jet Thrust Motor and Inverted Hydro Pulse. In April 1932, Fritz Zwicky married Dorothy Vernon Gates, a member of a prominent local family and her money was instrumental in the funding of the Palomar Observatory during the Great Depression. Nicholas Roosevelt, cousin of President Theodore Roosevelt, was his brother-in-law by marriage to Tirzah Gates, Zwicky and Dorothy divorced amicably in 1941. In 1947 Zwicky was married in Switzerland to Anna Margaritha Zurcher, Zwicky died in Pasadena on February 8,1974, and was buried in Mollis, Switzerland. He is remembered as both a genius and a curmudgeon, one of his favorite insults was to refer to people he did not approve of as spherical bastards, because, he explained, they were bastards no matter which way you looked at them. A recent biography in English was published by the Fritz Zwicky Foundation, Alfred Stöckli & Roland Müller, a review of the book is available from Acta Morphologica Generalis. Fritz Zwicky was a prolific scientist and made important contributions in areas of astronomy
38.
Dark matter
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Dark matter is an unidentified type of matter distinct from dark energy, baryonic matter, and neutrinos whose existence would explain a number of otherwise puzzling astronomical observations. The name refers to the fact that it does not emit or interact with radiation, such as light. The standard model of cosmology indicates that the total mass–energy of the universe contains 4. 9% ordinary matter,26. 8% dark matter and 68. 3% dark energy. Thus, dark matter constitutes 84. 5% of total mass, the most widely accepted hypothesis on the form for dark matter is that it is composed of weakly interacting massive particles that interact only through gravity and the weak force. All these lines of evidence suggest that galaxies, galaxy clusters, and the universe as a whole contain far more matter than that which is observable via electromagnetic signals. Many experiments to detect proposed dark matter particles through non-gravitational means are under way, however, no dark matter particle has been conclusively identified. ”In 1906 Henri Poincaré in the “The Milky Way and Theory of Gases” used dark matter, ” or “matière obscure” in French in discussing Kelvins work. The first to suggest the existence of matter was Dutch astronomer Jacobus Kapteyn in 1922. Fellow Dutchman and radio astronomy pioneer Jan Oort also hypothesized the existence of matter in 1932. In 1933, Swiss astrophysicist Fritz Zwicky, who studied galactic clusters while working at the California Institute of Technology, Zwicky applied the virial theorem to the Coma galaxy cluster and obtained evidence of unseen mass that he called dunkle Materie dark matter. Zwicky estimated its mass based on the motions of galaxies near its edge and compared that to an estimate based on its brightness and he estimated that the cluster had about 400 times more mass than was visually observable. The gravity effect of the galaxies was far too small for such fast orbits. Based on these conclusions, Zwicky inferred that some unseen matter provided the mass and this was the first formal inference about the existence of dark matter. However, Zwicky did correctly infer that the bulk of the matter was dark, the first robust indications that the mass to light ratio was anything other than unity came from measurements of galaxy rotation curves. In 1939, Horace W. Babcock reported the rotation curve for the Andromeda nebula and he attributed it to either light absorption within the galaxy or modified dynamics in the outer portions of the spiral and not to missing matter. Vera Rubin and Kent Ford in the 1960s–1970s provided further strong evidence, Rubin worked with a new spectrograph to measure the velocity curve of edge-on spiral galaxies with greater accuracy. This result was confirmed in 1978, an influential paper presented Rubins results in 1980. According to consensus among cosmologists, dark matter is composed primarily of a not yet characterized type of subatomic particle, the search for this particle, by a variety of means, is one of the major efforts in particle physics. In cosmology, the CMB is explained as relic radiation which has travelled freely since the era of recombination, the CMB’s anisotropies are explained as the result of small primordial density fluctuations, and subsequent acoustic oscillations in the photon-baryon plasma whose restoring force is gravity
39.
Jupiter
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Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, Jupiter and Saturn are gas giants, the other two giant planets, Uranus and Neptune are ice giants. Jupiter has been known to astronomers since antiquity, the Romans named it after their god Jupiter. Jupiter is primarily composed of hydrogen with a quarter of its mass being helium and it may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rotation, the planets shape is that of an oblate spheroid. The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence, a prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere, Jupiter has at least 67 moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a greater than that of the planet Mercury. Jupiter has been explored on several occasions by robotic spacecraft, most notably during the early Pioneer and Voyager flyby missions and later by the Galileo orbiter. In late February 2007, Jupiter was visited by the New Horizons probe, the latest probe to visit the planet is Juno, which entered into orbit around Jupiter on July 4,2016. Future targets for exploration in the Jupiter system include the probable ice-covered liquid ocean of its moon Europa, Earth and its neighbor planets may have formed from fragments of planets after collisions with Jupiter destroyed those super-Earths near the Sun. Astronomers have discovered nearly 500 planetary systems with multiple planets, Jupiter moving out of the inner Solar System would have allowed the formation of inner planets, including Earth. Jupiter is composed primarily of gaseous and liquid matter and it is the largest of the four giant planets in the Solar System and hence its largest planet. It has a diameter of 142,984 km at its equator, the average density of Jupiter,1.326 g/cm3, is the second highest of the giant planets, but lower than those of the four terrestrial planets. Jupiters upper atmosphere is about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, a helium atom has about four times as much mass as a hydrogen atom, so the composition changes when described as the proportion of mass contributed by different atoms. Thus, Jupiters atmosphere is approximately 75% hydrogen and 24% helium by mass, the atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds. There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, the outermost layer of the atmosphere contains crystals of frozen ammonia. The interior contains denser materials - by mass it is roughly 71% hydrogen, 24% helium, through infrared and ultraviolet measurements, trace amounts of benzene and other hydrocarbons have also been found
40.
Stellar population
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In 1944, Walter Baade categorized groups of stars within the Milky Way from their spectra. Two main divisions were defined as Population I and II, with another known as Population III added in 1978. By coincidence, each population group definition has decreasing metal content, hence, the first stars in the universe were deemed Population III, and recent stars are Population I. Population I stars are stars with high metallicity, while Population II stars are older stars with low metallicity. Observation of the spectra of stars has revealed that the metallicity of older stars have fewer heavy elements compared to the Sun and this immediately suggests that metallicity has evolved through the generations of stars by the process of stellar evolution. In current cosmological models, the matter created in the Big Bang was mostly hydrogen and helium, after this, when the universe cooled sufficiently, the first stars were born as extremely metal-poor Population III stars. Without metals, it is postulated that their masses were hundreds of times that of the Sun. In turn, these massive stars evolved very quickly, and their nucleosynthetic processes quickly created the first 26 elements, current theoretical stellar models show that most high-mass Population III stars quickly exhausted their fuel and exploded in extremely energetic pair-instability supernovae. Those explosions would have thoroughly dispersed their material, ejecting metals into the interstellar medium and their destruction suggests that no galactic high-mass Population III stars should be observable. However, some Population III stars might be seen in high-redshift galaxies whose light originated during the history of the universe. It has been proposed that recent supernovae SN 2006gy and SN 2007bi may have been pair-instability supernovae in which such super-massive Population III stars exploded. As those stars died, they returned metal-enriched material to the interstellar medium via planetary nebulae and supernovae and these youngest stars, including the Sun, therefore have the highest metal content, and are known as Population I stars. Population I, or metal-rich stars, are stars with the highest metallicity out of all three populations. The Earths Sun is an example of a metal-rich star and these are common in the spiral arms of the Milky Way galaxy. Generally, the youngest stars, the extreme Population I, are found farther toward the center of a galaxy, the Sun is an intermediate Population I star. Population I stars have regular elliptical orbits of the galactic centre, between the intermediate Population I and the Population II stars comes the intermediary disc population. Population II, or metal-poor stars, are those with little metal.8 billion years after the Big Bang. However, metal-poor objects are more primitive
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Cepheid variable
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A Cepheid variable is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude. This robust characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of stars in the Magellanic Clouds. This discovery allows one to know the true luminosity of a Cepheid by simply observing its pulsation period and this in turn allows one to determine the distance to the star, by comparing its known luminosity to its observed brightness. The term Cepheid originates from Delta Cephei in the constellation Cepheus, identified by John Goodricke in 1784, Cepheid variables are divided into two subclasses which exhibit markedly different masses, ages, and evolutionary histories, classical Cepheids and type II Cepheids. Delta Scuti variables are A class stars on or near the main sequence at the end of the instability strip and were originally referred to as dwarf Cepheids. RR Lyrae variables have short periods and lie on the instability strip where it crosses the horizontal branch, Delta Scuti variables and RR Lyrae variables are not generally treated with Cepheid variables although their pulsations originate with the same helium ionisation kappa mechanism. Classical Cepheids undergo pulsations with very regular periods on the order of days to months, classical Cepheids are Population I variable stars which are 4–20 times more massive than the Sun, and up to 100,000 times more luminous. These Cepheids are yellow bright giants and supergiants of spectral class F6 – K2, classical Cepheids are used to determine distances to galaxies within the Local Group and beyond, and are a means by which the Hubble constant can be established. Classical Cepheids have also used to clarify many characteristics of our galaxy, such as the Suns height above the galactic plane. A group of classical Cepheids with small amplitudes and sinusoidal light curves are often separated out as Small Amplitude Cepheids or s-Cepheids, type II Cepheids are population II variable stars which pulsate with periods typically between 1 and 50 days. Type II Cepheids are typically metal-poor, old, low mass objects, type II Cepheids are divided into several subgroups by period. Stars with periods between 1 and 4 days are of the BL Her subclass, 10–20 days belong to the W Virginis subclass, type II Cepheids are used to establish the distance to the Galactic Center, globular clusters, and galaxies. A group of pulsating stars on the instability strip have periods of less than 2 days, similar to RR Lyrae variables, anomalous Cepheid variables have masses higher than type II Cepheids, RR Lyrae variables, and our sun. It is unclear whether they are stars on a turned-back horizontal branch, blue stragglers formed through mass transfer in binary systems. A small proportion of Cepheid variables have been observed to pulsate in two modes at the time, usually the fundamental and first overtone, occasionally the second overtone. A very small number pulsate in three modes, or a combination of modes including higher overtones. On September 10,1784, Edward Pigott detected the variability of Eta Aquilae, however, the eponymous star for classical Cepheids is Delta Cephei, discovered to be variable by John Goodricke a few months later. A relationship between the period and luminosity for classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt in an investigation of thousands of stars in the Magellanic Clouds
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