Aphrodite Terra is a highland region on Venus, near the equator. Aphrodite Terra is named after the goddess of the Greek equivalent of the Roman goddess Venus, it is about the same size as Africa, much rougher than Ishtar Terra. The surface fractured which suggests large compressive forces. There are numerous extensive lava flows. Channels cross some have an interesting bow shape to them. Aphrodite Terra has mountain ranges but they are only about half the size of the mountains on Ishtar. Aphrodite Terra has Thetis Regio in the east. Ovda Regio has ridges running in two directions, suggesting that the compressive forces are acting in several directions. There are dark regions. There are series of cracks where lava has welled up through the surface and flooded the surrounding terrain. Vega 1 Vega 2 1. D. A. Senske, "Geology of the Venus equatorial region from Pioneer Venus radar imaging," Part 3 Regional Geology, Earth and Planets, July 1990, Volume 50, Issue 1, Springer, pp 305–327. 2. L. S. Crumpler, "Eastern Aphrodite Terra on Venus: Characteristics and mode of origin," Part 3 Regional Geology, Earth and Planets, July 1990, Volume 50, Issue 1, Springer, pp 343–388..
NASA Map of Venus
The National Aeronautics and Space Administration is an independent agency of the United States Federal Government responsible for the civilian space program, as well as aeronautics and aerospace research. NASA was established in 1958; the new agency was to have a distinctly civilian orientation, encouraging peaceful applications in space science. Since its establishment, most US space exploration efforts have been led by NASA, including the Apollo Moon landing missions, the Skylab space station, the Space Shuttle. NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle, the Space Launch System and Commercial Crew vehicles; the agency is responsible for the Launch Services Program which provides oversight of launch operations and countdown management for unmanned NASA launches. NASA science is focused on better understanding Earth through the Earth Observing System. From 1946, the National Advisory Committee for Aeronautics had been experimenting with rocket planes such as the supersonic Bell X-1.
In the early 1950s, there was challenge to launch an artificial satellite for the International Geophysical Year. An effort for this was the American Project Vanguard. After the Soviet launch of the world's first artificial satellite on October 4, 1957, the attention of the United States turned toward its own fledgling space efforts; the US Congress, alarmed by the perceived threat to national security and technological leadership, urged immediate and swift action. On January 12, 1958, NACA organized a "Special Committee on Space Technology", headed by Guyford Stever. On January 14, 1958, NACA Director Hugh Dryden published "A National Research Program for Space Technology" stating: It is of great urgency and importance to our country both from consideration of our prestige as a nation as well as military necessity that this challenge be met by an energetic program of research and development for the conquest of space... It is accordingly proposed that the scientific research be the responsibility of a national civilian agency...
NACA is capable, by rapid extension and expansion of its effort, of providing leadership in space technology. While this new federal agency would conduct all non-military space activity, the Advanced Research Projects Agency was created in February 1958 to develop space technology for military application. On July 29, 1958, Eisenhower signed the National Aeronautics and Space Act, establishing NASA; when it began operations on October 1, 1958, NASA absorbed the 43-year-old NACA intact. A NASA seal was approved by President Eisenhower in 1959. Elements of the Army Ballistic Missile Agency and the United States Naval Research Laboratory were incorporated into NASA. A significant contributor to NASA's entry into the Space Race with the Soviet Union was the technology from the German rocket program led by Wernher von Braun, now working for the Army Ballistic Missile Agency, which in turn incorporated the technology of American scientist Robert Goddard's earlier works. Earlier research efforts within the US Air Force and many of ARPA's early space programs were transferred to NASA.
In December 1958, NASA gained control of the Jet Propulsion Laboratory, a contractor facility operated by the California Institute of Technology. The agency's leader, NASA's administrator, is nominated by the President of the United States subject to approval of the US Senate, reports to him or her and serves as senior space science advisor. Though space exploration is ostensibly non-partisan, the appointee is associated with the President's political party, a new administrator is chosen when the Presidency changes parties; the only exceptions to this have been: Democrat Thomas O. Paine, acting administrator under Democrat Lyndon B. Johnson, stayed on while Republican Richard Nixon tried but failed to get one of his own choices to accept the job. Paine was confirmed by the Senate in March 1969 and served through September 1970. Republican James C. Fletcher, appointed by Nixon and confirmed in April 1971, stayed through May 1977 into the term of Democrat Jimmy Carter. Daniel Goldin was appointed by Republican George H. W. Bush and stayed through the entire administration of Democrat Bill Clinton.
Robert M. Lightfoot, Jr. associate administrator under Democrat Barack Obama, was kept on as acting administrator by Republican Donald Trump until Trump's own choice Jim Bridenstine, was confirmed in April 2018. Though the agency is independent, the survival or discontinuation of projects can depend directly on the will of the President; the first administrator was Dr. T. Keith Glennan appointed by Republican President Dwight D. Eisenhower. During his term he brought together the disparate projects in American space development research; the second administrator, James E. Webb, appointed by President John F. Kennedy, was a Democrat who first publicly served under President Harry S. Truman. In order to implement the Apollo program to achieve Kennedy's Moon la
In gamma-ray astronomy, gamma-ray bursts are energetic explosions that have been observed in distant galaxies. They are the brightest electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several hours. After an initial flash of gamma rays, a longer-lived "afterglow" is emitted at longer wavelengths; the intense radiation of most observed GRBs is thought to be released during a supernova or superluminous supernova as a high-mass star implodes to form a neutron star or a black hole. A subclass of GRBs appear to originate from a kilonova; the cause of the precursor burst observed in some of these short events may be the development of a resonance between the crust and core of such stars as a result of the massive tidal forces experienced in the seconds leading up to their collision, causing the entire crust of the star to shatter. The sources of most GRBs are billions of light years away from Earth, implying that the explosions are both energetic and rare.
All observed GRBs have originated from outside the Milky Way galaxy, although a related class of phenomena, soft gamma repeater flares, are associated with magnetars within the Milky Way. It has been hypothesized that a gamma-ray burst in the Milky Way, pointing directly towards the Earth, could cause a mass extinction event. GRBs were first detected in 1967 by the Vela satellites, designed to detect covert nuclear weapons tests. Following their discovery, hundreds of theoretical models were proposed to explain these bursts, such as collisions between comets and neutron stars. Little information was available to verify these models until the 1997 detection of the first X-ray and optical afterglows and direct measurement of their redshifts using optical spectroscopy, thus their distances and energy outputs; these discoveries, subsequent studies of the galaxies and supernovae associated with the bursts, clarified the distance and luminosity of GRBs, definitively placing them in distant galaxies.
Gamma-ray bursts were first observed in the late 1960s by the U. S. Vela satellites, which were built to detect gamma radiation pulses emitted by nuclear weapons tested in space; the United States suspected that the Soviet Union might attempt to conduct secret nuclear tests after signing the Nuclear Test Ban Treaty in 1963. On July 2, 1967, at 14:19 UTC, the Vela 4 and Vela 3 satellites detected a flash of gamma radiation unlike any known nuclear weapons signature. Uncertain what had happened but not considering the matter urgent, the team at the Los Alamos National Laboratory, led by Ray Klebesadel, filed the data away for investigation; as additional Vela satellites were launched with better instruments, the Los Alamos team continued to find inexplicable gamma-ray bursts in their data. By analyzing the different arrival times of the bursts as detected by different satellites, the team was able to determine rough estimates for the sky positions of sixteen bursts and definitively rule out a terrestrial or solar origin.
The discovery was declassified and published in 1973. Most early theories of gamma-ray bursts posited nearby sources within the Milky Way Galaxy. From 1991, the Compton Gamma Ray Observatory and its Burst and Transient Source Explorer instrument, an sensitive gamma-ray detector, provided data that showed the distribution of GRBs is isotropic—not biased towards any particular direction in space. If the sources were from within our own galaxy they would be concentrated in or near the galactic plane; the absence of any such pattern in the case of GRBs provided strong evidence that gamma-ray bursts must come from beyond the Milky Way. However, some Milky Way models are still consistent with an isotropic distribution. In October 2018, astronomers reported that GRB 150101B, a gamma-ray burst event detected in 2015, may be directly related to the historic GW170817, a gravitational wave event detected in 2017, associated with the merger of two neutron stars; the similarities between the two events, in terms of gamma ray, optical and x-ray emissions, as well as to the nature of the associated host galaxies, are "striking", suggesting the two separate events may both be the result of the merger of neutron stars, both may be a kilonova, which may be more common in the universe than understood, according to the researchers.
For decades after the discovery of GRBs, astronomers searched for a counterpart at other wavelengths: i.e. any astronomical object in positional coincidence with a observed burst. Astronomers considered many distinct classes of objects, including white dwarfs, supernovae, globular clusters, Seyfert galaxies, BL Lac objects. All such searches were unsuccessful, in a few cases well-localized bursts could be shown to have no bright objects of any nature consistent with the position derived from the detecting satellites; this suggested an origin of either faint stars or distant galaxies. The most accurate positions contained numerous faint stars and galaxies, it was agreed that final resolution of the origins of cosmic gamma-ray bursts would require both new satellites and faster communication. Several models for the origin of gamma-ray bursts postulated that the initial burst of gamma rays should be followed by fading emission at longer wavelengths created by collisions betwee
Lada Terra is a major landmass near the south pole of Venus, centered at 60°S and 20°E and has a diameter of 8,615 kilometres. It is defined by the International Astronomical Union as one of the three "major landmasses," or terrae, of Venus; the term "landmass" is not analogous to the landmass on Earth, as there are no apparent oceans on Venus. The term here applies to a substantial portion of land that lies above the average planetary radius, corresponds to highlands; the broad region of Lada Terra contains massive coronae, rift zones, volcanic plains as well as many other features that scientists use to attempt to piece together the history of this complex planet. The distinctive cross-cutting relationships found in the bedding of Lada Terra have been important in realizing relative ages of the extensional belts and coronae, as well as the complex tesserae features present planet-wide. In 1990 the Venus Radar Mapper revealed the largest outflow channel system on the planet located in the northern region of Lada Terra.
Although Lada Terra is considered a highland of Venus, the topography is much lower-lying than its northern counterparts Ishtar Terra and Aphrodite Terra. Lada Terra is named after the Slavic goddess of love. Lada Terra is one of eight distinct regions on the surface of Venus. Ishtar Terra and Aphrodite Terra are the other significant terrae of the planet, located near the northern polar region and the equator, respectively. Lada Terra has a diameter of 8,615 kilometres. and covers most of the south pole region on Venus. The region consists of deformed terrains indicating crustal deformation processes effecting the area in the past; the lowlands are much smoother terrain with little deformation, which scientists postulate to be young lava flow remnants. The most prominent region is the midlands, where sloping topography is disrupted by faults and corona, making this area the most complex and studied region in Lada Terra; the western portion of Lada Terra contains a large dome-shaped structure about 2,000 kilometres across termed, "the Lada Rise,", the main highland of the region.
It reaches an elevation of about 3 kilometres and is dominated by one of the most massive corona in the solar system, the Quetzalpetlatl Corona, as well as two massive rift zones surround and intersect the rise. The high rises of Venus fall into the corona-dominated or rift-dominated categories, but the Lada Rise is unique in that it contains both of these features in equal amounts. In 2007, data retrieved from the Venus Express mission using the Visible and Infrared Thermal Imaging Spectrometer revealed high emissivity anomalies, interpreted by many scientists to be a hotspot analogous to the Hawaii hot spot on Earth. This, along with the positive gravity anomaly observed, implies a active region. Further evidence is observed in the Boala Corona, where the grabens formed in the depression of the Corona are interpreted to be surface manifestations of terrestrial dikes; the mantle upwelling associated with hot spot tectonism appears to be the dominant process which formed and evolved the Lada Rise.
A rift about 6,000 kilometres long and 200 kilometres wide, named the Alpha-Lada extensional belt, spans the northwestern edge of Lada Terra separating the high lands of Lada Terra from the broad lowlands of Lavinia Planitia. The Lavinia Planitia basin is suspected to be an area of mantle downwelling, where there are less thermal stresses on the lithosphere; because the nearby Lada Rise is speculated to be an area of mantle upwelling, models predict this could create a zone of weakness between these two convection cells which stretches the lithosphere, thus creating the rift zone. Associated with the rift zone are large lava flow fields and corona; the bedding relationships between the rift zone and these volcanic structures indicate they were formed about the same time, which many interpret as lava finding a preferential route to the surface through these newly formed fractures. A second rift, named the Ammavuro-Quetzalpetlatl extensional belt, is a 2,000 kilometres long and 300 kilometres wide rift which lies in the northeast region of Lada Terra.
These two massive rifts intersect in the northern region of Lada Terra, the observed deformation of the two extensional belts seems to have occurred at the same time, although the larger Alpha-Lada rift most continued to be deformed for a longer period. Unlike most coronae on the planet, which are about 200 kilometres in diameter, Quetzalpetlatl Corona has a diameter of about 800 kilometres, it is the third most massive corona after Artemis Corona and Heng-O Corona, lies on the Lada Rise, with part of the corona intersecting the Ammavuro-Quetzalpetlatl belt in the northwestern region of Lada Terra. The corona consists of a raised inner region surrounded by the lower-lying "corona floor," with an elevated ridge about 1–2 kilometres above the corona floor, as well as an outer "moat" of depressed terrain, 200–300 metres below the surrounding land; the corona is characterized by massive lava flows that cover 600,000 square kilometres of the Venusian surface, the largest lava flow extent seen on the planet to date.
We can draw an analogue of this lava flow to a flow that occurred on earth, the Deccan Traps igneous province in India. Compared to other corona on Venus, Quetzalpetlatl Corona not only exhibits the most massive lava flow, but is composed of lava of homogeneous composition as revealed by the variations in brightness using radar backscatter imaging; this is in c
A nephelometer is an instrument for measuring the concentration of suspended particulates in a liquid or gas colloid. A nephelometer measures suspended particulates by employing a light beam and a light detector set to one side of the source beam. Particle density is a function of the light reflected into the detector from the particles. To some extent, how much light reflects for a given density of particles is dependent upon properties of the particles such as their shape and reflectivity. Nephelometers are calibrated to a known particulate use environmental factors to compensate lighter or darker colored dusts accordingly. K-factor is determined by the user by running the nephelometer next to an air sampling pump and comparing results. There are a wide variety of research-grade nephelometers on the market as well as open source varieties; the main uses of nephelometers relate to air quality measurement for pollution monitoring, climate monitoring, visibility. Airborne particles are either biological contaminants, particulate contaminants, gaseous contaminants, or dust.
The chart to the left shows the sizes of various particulate contaminants. This information is helpful toward understanding the character of particulate pollution inside a building or in the ambient air, it is useful for understanding the cleanliness level in a controlled environment. Biological contaminants include mold, bacteria, animal dander, dust mites, human skin cells, cockroach parts, or anything alive or living at one time, they are the biggest enemy of indoor air quality specialists because they are contaminants that cause health problems. Levels of biological contamination depend on humidity and temperature that supports the livelihood of micro-organisms; the presence of pets, plants and insects will raise the level of biological contamination. Sheath air is clean filtered air that surrounds the aerosol stream to prevent particulates from circulating or depositing within the optic chamber. Sheath air prevents contamination caused by build-up and deposits, improves response time by containing the sample, improves maintenance by keeping the optic chamber clean.
The nephelometer creates the sheath air by passing air through a zero filter before beginning the sample. Nephelometers are used in global warming studies measuring the global radiation balance. Three wavelength nephelometers fitted with a backscatter shutter can determine the amount of solar radiation, reflected back into space through dust and particulate matter; this reflected light influences the amount of radiation reaching the earth's lower atmosphere and warming the planet. Nephelometers are used for measurement of visibility with simple one-wavelength nephelometers used throughout the world by many EPAs. Nephelometers, through the measurement of light scattering, can determine visibility in distance through the application of a conversion factor called Koschmieder's formula. In medicine, nephelometry is used to measure immune function. Gas-phase nephelometers are used in the detection of smoke and other particles of combustion. In such use, the apparatus is referred to as an aspirated smoke detector.
These have the capability to detect low particle concentrations and are therefore suitable to protecting sensitive or valuable electronic equipment, such as mainframe computers and telephone switches. Because optical properties depend on suspended particle size, a stable synthetic material called "Formazin" with uniform particle size is used as a standard for calibration and reproducibility; the unit is called Formazin Turbidity Unit. Nephelometric Turbidity Units specified by United States Environmental Protection Agency is a special case of FTU, where a white light source and certain geometrical properties of the measurement apparatus are specified. Formazin Nephelometric Units, prescribed for 9 measurements of turbidity in water treatment by ISO 7027, another special case of FTU with near infrared light and 90° scatter. Formazin Attenuation Units specified by ISO 7027 for water treatment standards for turbidity measurements at 0° a special case of FTU. Formazin Backscatter Units, not part of a standard, is the unit of optical backscatter detectors, measured at c.
180° a special case of FTU. European Brewery Convention turbidity units Concentration Units Optical Density Jackson "Candle" Turbidity Units Helms Units American Society of Brewing Chemists turbidity units Parts Per Million of standard substance, such as PPM/DE "Trübungseinheit/Formazin" a German standard, now replaced by the FNU unit. Diatomaceous earth an older standard, now obsoleteA more popular term for this instrument in water quality testing is a turbidimeter. However, there can be differences between models of turbidimeters, depending upon the arrangement of the source beam and the detector. A nephelometric turbidimeter always monitors light reflected off the particles and not attenuation due to cloudiness. In the United States environmental monitoring the turbidity standard unit is called Nephelometric Turbidity Units, while the international standard unit is called Formazin Nephelometric Unit; the most applicable unit is Formazin Turbidity Unit, although different measurement methods can give quite different values as reported in FTU.
Gas-phase nephelometers are used to study the atmosphere. These can provide information on atmospheric albedo. ISO 7027 Water purification
The ionosphere is the ionized part of Earth's upper atmosphere, from about 60 km to 1,000 km altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation, it forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth; as early as 1839, the German mathematician and physicist Carl Friedrich Gauss postulated that an electrically conducting region of the atmosphere could account for observed variations of Earth's magnetic field. Sixty years Guglielmo Marconi received the first trans-Atlantic radio signal on December 12, 1901, in St. John's, Newfoundland using a 152.4 m kite-supported antenna for reception. The transmitting station in Poldhu, used a spark-gap transmitter to produce a signal with a frequency of 500 kHz and a power of 100 times more than any radio signal produced; the message received was three dits, the Morse code for the letter S.
To reach Newfoundland the signal would have to bounce off the ionosphere twice. Dr. Jack Belrose has contested this, based on theoretical and experimental work. However, Marconi did achieve transatlantic wireless communications in Glace Bay, Nova Scotia, one year later. In 1902, Oliver Heaviside proposed the existence of the Kennelly–Heaviside layer of the ionosphere which bears his name. Heaviside's proposal included means by which radio signals are transmitted around the Earth's curvature. Heaviside's proposal, coupled with Planck's law of black-body radiation, may have hampered the growth of radio astronomy for the detection of electromagnetic waves from celestial bodies until 1932. In 1902, Arthur Edwin Kennelly discovered some of the ionosphere's radio-electrical properties. In 1912, the U. S. Congress imposed the Radio Act of 1912 on amateur radio operators, limiting their operations to frequencies above 1.5 MHz. The government thought; this led to the discovery of HF radio propagation via the ionosphere in 1923.
In 1926, Scottish physicist Robert Watson-Watt introduced the term ionosphere in a letter published only in 1969 in Nature: We have in quite recent years seen the universal adoption of the term'stratosphere'..and..the companion term'troposphere'... The term'ionosphere', for the region in which the main characteristic is large scale ionisation with considerable mean free paths, appears appropriate as an addition to this series. In the early 1930s, test transmissions of Radio Luxembourg inadvertently provided evidence of the first radio modification of the ionosphere. Edward V. Appleton was awarded a Nobel Prize in 1947 for his confirmation in 1927 of the existence of the ionosphere. Lloyd Berkner first measured the density of the ionosphere; this permitted the first complete theory of short-wave radio propagation. Maurice V. Wilkes and J. A. Ratcliffe researched the topic of radio propagation of long radio waves in the ionosphere. Vitaly Ginzburg has developed a theory of electromagnetic wave propagation in plasmas such as the ionosphere.
In 1962, the Canadian satellite Alouette 1 was launched to study the ionosphere. Following its success were Alouette 2 in 1965 and the two ISIS satellites in 1969 and 1971, further AEROS-A and -B in 1972 and 1975, all for measuring the ionosphere. On July 26, 1963 the first operational geosynchronous satellite Syncom 2 was launched; the board radio beacons on this satellite enabled – for the first time – the measurement of total electron content variation along a radio beam from geostationary orbit to an earth receiver. Australian geophysicist Elizabeth Essex-Cohen from 1969 onwards was using this technique to monitor the atmosphere above Australia and Antarctica; the ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth, stretching from a height of about 50 km to more than 1,000 km. It exists due to ultraviolet radiation from the Sun; the lowest part of the Earth's atmosphere, the troposphere extends from the surface to about 10 km. Above, the stratosphere, followed by the mesosphere.
In the stratosphere incoming solar radiation creates the ozone layer. At heights of above 80 km, in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion; the number of these free electrons is sufficient to affect radio propagation. This portion of the atmosphere is ionized and contains a plasma, referred to as the ionosphere. Ultraviolet, X-ray and shorter wavelengths of solar radiation are ionizing, since photons at these frequencies contain sufficient energy to dislodge an electron from a neutral gas atom or molecule upon absorption. In this process the light electron obtains a high velocity so that the temperature of the created electronic gas is much higher than the one of ions and neutrals; the reverse process to ionization is recombination, in which a free electron is "captured" by a positive ion. Recombination occurs spontaneously, causes the emission of a photon carrying away the energy produced upon recombination.
As gas density increases at lower altitudes, the recombination process prevails, since the gas molecules and ions are closer together. The balance between these two processes determines th