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High Sensitivity Array
The Very Long Baseline Array (VLBA) is a system of ten radio telescopes which are operated remotely from their Array Operations Center located in Socorro, New Mexico, as a part of the National Radio Astronomy Observatory (NRAO). These ten radio antennas work together as an array that forms the longest system in the world that uses very long baseline interferometry. The longest baseline available in this interferometer is about . The construction of the VLBA began in February 1986 and it was completed in May 1993. The first astrometry, astrometrical observation using all ten antennas was carried out on May 29, 1993. The total cost of building the VLBA was about $85 million. The array is funded by the National Science Foundation, and costs about $10 million a year to operate. Each receiver in the VLBA consists of a dish antenna, parabolic dish antenna 25 meters (82 feet) in diameter, along with its adjacent control building. This contains the supporting electronics and machinery ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radio Telescope
A radio telescope is a specialized antenna (radio), antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum, just as optical telescopes are used to make observations in the visible light, visible portion of the spectrum in traditional optical astronomy. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night. Since astronomical radio sources such as planets, stars, nebulas and galaxy, galaxies are very far away, the radio waves coming from them are extremely weak, so radio telescopes require very large antennas to collect enough radio energy to study them, and extremely sensitive receiving equipment. Radio telescopes are typically large Parabolic antenna, parabolic ("dish") antennas similar to those employed in tracking and communicating with satellites an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atomic Clock
An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions between such states they interact with a very specific frequency of electromagnetic radiation. This phenomenon serves as the basis for the International System of Units' (SI) definition of a second: The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, \Delta \nu_\text, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be when expressed in the unit Hz, which is equal to s−1. This definition is the basis for the system of International Atomic Time (TAI), which is maintained by an ensemble of atomic clocks around the world. The system of Coordinated Universal Time, Coordinated Universal Time (UTC) that is the basis of civil time implements ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geographic Coordinate System
A geographic coordinate system (GCS) is a spherical coordinate system, spherical or geodetic coordinates, geodetic coordinate system for measuring and communicating position (geometry), positions directly on Earth as latitude and longitude. It is the simplest, oldest, and most widely used type of the various spatial reference systems that are in use, and forms the basis for most others. Although latitude and longitude form a coordinate tuple like a cartesian coordinate system, the geographic coordinate system is not cartesian because the measurements are angles and are not on a planar surface. A full GCS specification, such as those listed in the EPSG Geodetic Parameter Dataset, EPSG and ISO 19111 standards, also includes a choice of geodetic datum (including an Earth ellipsoid), as different datums will yield different latitude and longitude values for the same location. History The invention of a geographic coordinate system is generally credited to Eratosthenes of Cy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Toponymy
Toponymy, toponymics, or toponomastics is the study of '' toponyms'' ( proper names of places, also known as place names and geographic names), including their origins, meanings, usage, and types. ''Toponym'' is the general term for a proper name of any geographical feature, and full scope of the term also includes proper names of all cosmographical features. In a more specific sense, the term ''toponymy'' refers to an inventory of toponyms, while the discipline researching such names is referred to as ''toponymics'' or ''toponomastics''. Toponymy is a branch of onomastics, the study of proper names of all kinds. A person who studies toponymy is called ''toponymist''. Etymology The term ''toponymy'' comes from / , 'place', and / , 'name'. The '' Oxford English Dictionary'' records ''toponymy'' (meaning "place name") first appearing in English in 1876 in the context of geographical studies. Since then, ''toponym'' has come to replace the term ''place-name'' in professional ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Contiguous United States
The contiguous United States, also known as the U.S. mainland, officially referred to as the conterminous United States, consists of the 48 adjoining U.S. states and the District of Columbia of the United States in central North America. The term excludes the only two non- contiguous states and the last two to be admitted to the Union, which are Alaska and Hawaii, and all other offshore insular areas, such as the U.S. territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands. The colloquial term ''Lower48'' is also used, especially in relation to Alaska. The term The Mainland is used in Hawaii. The related but distinct term ''continental United States'' includes Alaska, which is also on North America, but separated from the 48 states by British Columbia in Canada, but excludes Hawaii and all the insular areas in the Caribbean and the Pacific. The greatest distance on a great-circle route entirely within the contiguous U.S. i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequency Band
Spectral bands are regions of a given spectrum, having a specific range of wavelengths or frequencies. Most often, it refers to electromagnetic bands, regions of the electromagnetic spectrum. More generally, spectral bands may also be means in the spectra of other types of signals, e.g., noise spectrum. A frequency band is an interval in the frequency domain, limited by a lower frequency and an upper frequency. For example, it may refer to a '' radio band'', such as wireless communication standards set by the International Telecommunication Union. In nuclear physics In nuclear physics, spectral bands refer to the electromagnetic emission of polyatomic systems, including condensed materials, large molecules, etc. Each '' spectral line'' corresponds to the difference in two energy levels of an atom. In molecules, these levels can split. When the number of atoms is large, one gets a continuum of energy levels, the so-called ''spectral bands''. They are often labeled in the sam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gigahertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base units is 1/s or s−1, meaning that one hertz is one per second or the reciprocal of one second. It is used only in the case of periodic events. It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. For high frequencies, the unit is commonly expressed in multiples: kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz). Some of the unit's most common uses are in the description of periodic waveforms and musical tones, particularly those used in radio- and audio-related applications. It is also used to describe the clock speeds at which computers and other electronics are driven. The units are sometimes also used as a representation of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frequencies
Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light. The interval of time between events is called the period. It is the reciprocal of the frequency. For example, if a heart beats at a frequency of 120 times per minute (2 hertz), its period is one half of a second. Special definitions of frequency are used in certain contexts, such as the angular frequency in rotational or cyclical properties, when the rate of angular progress is measured. Spatial frequency is defined for properties that vary or cccur repeatedly in geometry or space. The unit of measurement of frequency in the International System of Units (SI) is the hertz, having the symbol Hz. Definitions and units For cyclical phenomena such as oscillations, waves, or for examples ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Centimeter
upright=1.35, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is in-between 1 meter to 1 millimeter. A centimetre (International spelling) or centimeter (American English), with SI symbol cm, is a Units of measurement, unit of length in the International System of Units (SI) equal to one hundredth of a metre, ''centi-'' being the SI prefix for a factor of . Equivalently, there are 100 centimetres in 1 metre. The centimetre was the base unit of length in the now deprecated centimetre–gram–second (CGS) system of units. Though for many physical quantities, SI prefixes for factors of 103—like ''milli-'' and ''kilo-''—are often preferred by technicians, the centimetre remains a practical unit of length for many everyday measurements; for instance, human height is commonly measured in centimetres. A centimetre is approximately the width of the fingernail of an average adult person. Equivalence ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Millimeter
330px, Different lengths as in respect of the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 metre to 1 millimetre. The millimetre (American and British English spelling differences#-re, -er, international spelling; International System of Units, SI unit symbol mm) or millimeter (American and British English spelling differences#-re, -er, American spelling) is a Units of measurement, unit of length in the International System of Units (SI), equal to one thousandth of a metre, which is the SI base unit of length. Therefore, there are one thousand millimetres in a metre, and there are ten millimetres in a centimetre. One millimetre is equal to micrometres or nanometres. Since an inch is officially defined as exactly 25.4 millimetres, a millimetre is equal to exactly (≈ 0.03937) of an inch. Definition Since 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves), phase'' on the wave, such as two adjacent crests, troughs, or zero crossings. Wavelength is a characteristic of both traveling waves and standing waves, as well as other spatial wave patterns. The multiplicative inverse, inverse of the wavelength is called the ''spatial frequency''. Wavelength is commonly designated by the Greek letter lambda (''λ''). For a modulated wave, ''wavelength'' may refer to the carrier wavelength of the signal. The term ''wavelength'' may also apply to the repeating envelope (mathematics), envelope of modulated waves or waves formed by Interference (wave propagation), interference of several sinusoids. Assuming a sinusoidal wave moving at a fixed phase velocity, wave speed, wavelength is inversely proportion ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Observation
Observation in the natural sciences is an act or instance of noticing or perceiving and the acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data via the use of scientific instruments. The term may also refer to any data collected during the scientific activity. Observations can be qualitative, that is, the absence or presence of a property is noted and the observed phenomenon described, or quantitative if a numerical value is attached to the observed phenomenon by counting or measuring. Science The scientific method requires observations of natural phenomena to formulate and test hypotheses. It consists of the following steps: # Ask a question about a phenomenon # Make observations of the phenomenon # Formulate a hypothesis that tentatively answers the question # Predict logical, observable consequences of the hypothesis that have not yet been inv ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
