|
Green Bank Radio Telescope
The Robert C. Byrd Green Bank Telescope (GBT) in Green Bank, West Virginia, US is the world's largest fully steerable radio telescope, surpassing the Effelsberg 100-m Radio Telescope in Germany. The Green Bank site was part of the National Radio Astronomy Observatory (NRAO) until September 30, 2016. Since October 1, 2016, the telescope has been operated by the independent Green Bank Observatory. The telescope's name honors the late Senator Robert C. Byrd who represented West Virginia and who pushed the funding of the telescope through Congress. The Green Bank Telescope operates at meter to millimeter wavelengths. Its 100-meter diameter collecting area, unblocked aperture, and good surface accuracy provide superb sensitivity across the telescope's full 0.1–116 GHz operating range. The GBT is fully steerable, and 85 percent of the local celestial hemisphere is accessible. It is used for astronomy about 6500 hours every year, with 2000–3000 hours per year going to high-f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
West Virginia
West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the Bureau of Labor Statistics classifies the state as a part of the Mid-Atlantic regionMid-Atlantic Home : Mid-Atlantic Information Office: U.S. Bureau of Labor Statistics" www.bls.gov. Archived. It is bordered by Pennsylvania to the north and east, Maryland to the east and northeast, Virginia to the southeast, Kentucky to the southwest, and Ohio to the northwest. West Virginia is the 10th-smallest state by area and ranks as the 12th-least populous state, with a population of 1,793,716 residents. The capital and largest city is Charleston. West Virginia was admitted to the Union on June 20, 1863, and was a key border state during the American Civil War. It was the only state to form by separating from a Confederate state, the second to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
United States National Forest
In the United States, national forest is a classification of protected and managed federal lands. National forests are largely forest and woodland areas owned collectively by the American people through the federal government, and managed by the United States Forest Service, a division of the United States Department of Agriculture. The U.S. Forest Service is also a forestry research organization who provides financial assistance to state and local forestry industry. As of 2020, there are 154 national forests in the United States. History The National Forest System (NFS) was created by the Land Revision Act of 1891, which was enacted during the presidency of Benjamin Harrison. This act took land to form national parks in the West, including 15 reserves containing more than 13 million acres of land. At first one would be called a Forest Reserve; a later one would be termed a National Forest. It was the result of concerted action by Los Angeles-area businessmen and prope ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pulsar
A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Earth (similar to the way a lighthouse can be seen only when the light is pointed in the direction of an observer), and is responsible for the pulsed appearance of emission. Neutron stars are very dense and have short, regular rotational periods. This produces a very precise interval between pulses that ranges from milliseconds to seconds for an individual pulsar. Pulsars are one of the candidates for the source of ultra-high-energy cosmic rays. (See also centrifugal mechanism of acceleration.) The periods of pulsars make them very useful tools for astronomers. Observations of a pulsar in a binary neutron star system were used to indirectly confirm the existence of gravitational radiation. The first extrasolar planets were discovered aroun ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
The Washington Post
''The Washington Post'' (also known as the ''Post'' and, informally, ''WaPo'') is an American daily newspaper published in Washington, D.C. It is the most widely circulated newspaper within the Washington metropolitan area and has a large national audience. Daily broadsheet editions are printed for D.C., Maryland, and Virginia. The ''Post'' was founded in 1877. In its early years, it went through several owners and struggled both financially and editorially. Financier Eugene Meyer (financier), Eugene Meyer purchased it out of bankruptcy in 1933 and revived its health and reputation, work continued by his successors Katharine Graham, Katharine and Phil Graham (Meyer's daughter and son-in-law), who bought out several rival publications. The ''Post'' 1971 printing of the Pentagon Papers helped spur opposition to the Vietnam War. Subsequently, in the best-known episode in the newspaper's history, reporters Bob Woodward and Carl Bernstein led the American press's investigation into ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Statue Of Liberty
The Statue of Liberty (''Liberty Enlightening the World''; French: ''La Liberté éclairant le monde'') is a colossal neoclassical sculpture on Liberty Island in New York Harbor in New York City, in the United States. The copper statue, a gift from the people of France, was designed by French sculptor Frédéric Auguste Bartholdi and its metal framework was built by Gustave Eiffel. The statue was dedicated on October 28, 1886. The statue is a figure of Libertas, a robed Roman liberty goddess. She holds a torch above her head with her right hand, and in her left hand carries a '' tabula ansata'' inscribed JULY IV MDCCLXXVI (July 4, 1776 in Roman numerals), the date of the U.S. Declaration of Independence. A broken shackle and chain lie at her feet as she walks forward, commemorating the recent national abolition of slavery. After its dedication, the statue became an icon of freedom and of the United States, seen as a symbol of welcome to immigrants arriving by sea. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gregorian Telescope
The Gregorian telescope is a type of reflecting telescope designed by Scottish mathematician and astronomer James Gregory in the 17th century, and first built in 1673 by Robert Hooke. James Gregory was a contemporary of Isaac Newton. Both often worked simultaneously on similar projects. Gregory's design was published in 1663 and pre-dates the first practical reflecting telescope, the Newtonian telescope, built by Sir Isaac Newton in 1668."Isaac Newton: adventurer in thought", by Alfred Rupert Hallpage 67 However, Gregory's design was only a theoretical description, and he never actually constructed the telescope. It was not successfully built until five years after Newton's first reflecting telescope. History The Gregorian telescope is named after the James Gregory design, which appeared in his 1663 publication (The Advance of Optics). Similar theoretical designs have been found in the writings of Bonaventura Cavalieri ( (On Burning Mirrors), 1632) and Marin Mersenne (, 16 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Secondary Mirror
A secondary mirror (or secondary) is the second deflecting or focusing mirror element in a reflecting telescope. Light gathered by the primary mirror is directed towards a focal point typically past the location of the secondary. Secondary mirrors in the form of an optically flat ''diagonal mirror'' are used to re-direct the light path in designs such as Newtonian reflectors. They are also used to re-direct and extend the light path and modify the final image in designs such as Cassegrain reflectors. The secondary is typically suspended by X-shaped struts (sometimes called a "spider") in the path of light between the source and the primary, but can be mounted on other types of mounts or optical elements such as optical windows, or schmidt and meniscus corrector plates. Employing secondary mirrors in optical systems causes some image distortion due to the obstruction of the secondary itself, and distortion from the spider mounts, commonly seen as cross-shaped diffraction spikes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feed Horn
A feed horn (or feedhorn) is a small horn antenna used to couple a waveguide to e.g. a parabolic dish antenna or offset dish antenna for reception or transmission of microwave. A typical application is the use for satellite television reception with a satellite dish. In that case the feed horn can either be a separate part used together with e.g. a " low-noise block downconverter" (LNB), or more typically today is integrated into a "low-noise block feedhorn" (LNBF). Principle of operation The feed horn minimizes the mismatch loss between the antenna and the waveguide. If a simple open-ended waveguide would be used, without the horn, the sudden end of the conductive walls causes an abrupt impedance change at the aperture, between the wave impedance in the waveguide and the impedance of free space (see horn antenna for more details). When used with a offset, parabolic or lens antenna, the phase center of the horn is placed at the focal point of the reflector. The charact ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Focus (optics)
In geometrical optics, a focus, also called an image point, is a point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, which is caused by diffraction from the optical system's aperture. Aberrations tend to worsen as the aperture diameter increases, while the Airy circle is smallest for large apertures. An image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, and out of focus if light is not well converged. The border between these is sometimes defined using a " circle of confusion" criterion. A principal focus or focal point is a special focus: * For a lens, or a spherical or parabolic mirror, it is a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Satellite Television
Satellite television is a service that delivers television programming to viewers by relaying it from a communications satellite orbiting the Earth directly to the viewer's location. The signals are received via an outdoor parabolic antenna commonly referred to as a satellite dish and a low-noise block downconverter. A satellite receiver then decodes the desired television program for viewing on a television set. Receivers can be external set-top boxes, or a built-in television tuner. Satellite television provides a wide range of channels and services. It is usually the only television available in many remote geographic areas without terrestrial television or cable television service. Modern systems signals are relayed from a communications satellite on the X band (8–12 GHz) or Ku band (12–18 GHz) frequencies requiring only a small dish less than a meter in diameter. The first satellite TV systems were an obsolete type now known as television receive-only ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Root Mean Square
In mathematics and its applications, the root mean square of a set of numbers x_i (abbreviated as RMS, or rms and denoted in formulas as either x_\mathrm or \mathrm_x) is defined as the square root of the mean square (the arithmetic mean of the squares) of the set. The RMS is also known as the quadratic mean (denoted M_2) and is a particular case of the generalized mean. The RMS of a continuously varying function (denoted f_\mathrm) can be defined in terms of an integral of the squares of the instantaneous values during a cycle. For alternating electric current, RMS is equal to the value of the constant direct current that would produce the same power dissipation in a resistive load. In estimation theory, the root-mean-square deviation of an estimator is a measure of the imperfection of the fit of the estimator to the data. Definition The RMS value of a set of values (or a continuous-time waveform) is the square root of the arithmetic mean of the squares of the values, or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
