space probe is a scientific space exploration mission in which a robotic spacecraft leaves the gravity well of Earth and approaches the Moon or enters interplanetary or interstellar space (see list of probes by operational status for a list of active probes); The space agencies of the USSR (now Russia and Ukraine), the United States, the European Union, Japan, India and China have in the aggregate launched probes to several planets and moons of the solar system as well as to a number of asteroids and comets.

Adapted from the Wikipedia article Space probe, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1& mm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust (such as in the zodiacal cloud) and circumplanetary dust (such as in a planetary ring).

In our own Solar System, interplanetary dust causes the zodiacal light. Sources include comet dust, asteroidal dust, dust from the Kuiper belt, and interstellar dust passing through our solar system.

The terminology has no specific application for describing materials found on the planet Earth, other than in the most general sense that all elements with an atomic mass higher than hydrogen are believed to be formed in the core of stars via stellar nucleosynthesis and supernova nucleosynthesis events. As such all elements that exist can be indiscriminately considered to be a form of “cosmic dust”.

Adapted from the Wikipedia article Cosmic dust, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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James Clerk Maxwell Telescope (JCMT) is an infrared telescope with a primary mirror diameter of 15 metres (16.4 yards), also called a submillimetre-wavelength telescope. It is located at Mauna Kea Observatory in Hawaii. It is the largest astronomical telescope in the world designed specifically to operate in the submillimetre regime (between the far-infrared and the microwave regions of the electromagnetic spectrum). It is used to study our Solar System, interstellar dust and gas, and distant galaxies.

The JCMT is funded by a partnership between the United Kingdom, Canada, and the Netherlands. It is operated by the Joint Astronomy Centre and was named in honour of James Clerk Maxwell. It is located near the summit of Mauna Kea at an altitude of 13,425 feet (4092 m) as part of the Mauna Kea Observatory. The JCMT has the second largest telescope mirror on Mauna Kea (largest is the VLBA antenna).

This telescope was combined with the Caltech Submillimeter Observatory to form the first submillimeter interferometer. The success of this experiment was important in pushing ahead the construction of the Submillimeter Array and the Atacama Large Millimeter Array interferometers.

Adapted from the Wikipedia article James Clerk Maxwell Telescope, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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The NOVAS library provides three levels of subroutines (functions): basic, utility, and supervisory. Basic-level subroutines supply the values of fundamental variables, such as the nutation angles and the heliocentric positions of solar system bodies for specific epoches. Utility-level subroutines perform transformations, such as those caused by precession, nutation and aberration. Supervisory-level subroutines serve as interfaces to the basic and utility subroutines to compute the coordinates of stars or solar system bodies for specific dates and times.

Adapted from the Wikipedia article Naval Observatory Vector Astrometry Subroutines, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Solar astronomy

The solar system is subdivided into the inner planets, the asteroid belt, and the outer planets. The inner terrestrial planets consist of Mercury, Venus, Earth, and Mars. The outer gas giant planets are Jupiter, Saturn, Uranus, and Neptune. Beyond Neptune lies the Kuiper Belt, and finally the Oort Cloud, which may extend as far as a light-year.

The planets were formed in the protoplanetary disk that surrounded the early Sun. Through a process that included gravitational attraction, collision, and accretion, the disk formed clumps of matter that, with time, became protoplanets. The radiation pressure of the solar wind then expelled most of the unaccreted matter, and only those planets with sufficient mass retained their gaseous atmosphere. The planets continued to sweep up, or eject, the remaining matter during a period of intense bombardment, evidenced by the many impact craters on the Moon. During this period, some of the protoplanets may have collided, the leading hypothesis for how the Moon was formed.

Once a planet reaches sufficient mass, the materials with different densities segregate within, during planetary differentiation. This process can form a stony or metallic core, surrounded by a mantle and an outer surface. The core may include solid and liquid regions, and some planetary cores generate their own magnetic field, which can protect their atmospheres from solar wind stripping.

A planet or moon’s interior heat is produced from the collisions that created the body, radioactive materials (”e.g.” uranium, thorium, and 26A

Stellar astronomy

The study of stars and stellar evolution is fundamental to our understanding of the universe. The astrophysics of stars has been determined through observation and theoretical understanding; and from computer simulations of the interior.

Star formation occurs in dense regions of dust and gas, known as giant molecular clouds. When destabilized, cloud fragments can collapse under the influence of gravity, to form a protostar. A sufficiently dense, and hot, core region will trigger nuclear fusion, thus creating a main-sequence star.

Almost all elements heavier than hydrogen and helium were created inside the cores of stars.

The characteristics of the resulting star depend primarily upon its starting mass. The more massive the star, the greater its luminosity, and the more rapidly it expends the hydrogen fuel in its core. Over time, this hydrogen fuel is completely converted into helium, and the star begins to evolve. The fusion of helium requires a higher core temperature, so that the star both expands in size, and increases in core density. The resulting red giant enjoys a brief life span, before the helium fuel is in turn consumed. Very massive stars can also undergo a series of decreasing evolutionary phases, as they fuse increasingly heavier elements.

The final fate of the star depends on its mass, with stars of mass greater than about eight times the Sun becoming core collapse supernovae; while smaller stars form planetary nebulae, and evolve into white dwarfs. The remnant of a supernova is a dense neutron star, or, if the stellar mass was at least three times that of the Sun, a black hole. Close binary stars can follow more complex evolutionary paths, such as mass transfer onto a white dwarf companion that can potentially cause a supernova. Planetary nebulae and supernovae are necessary for the distribution of metals to the interstellar medium; without them, all new stars (and their planetary systems) would be formed from hydrogen and helium alone.

Galactic astronomy

The study of objects outside our galaxy is a branch of astronomy concerned with the formation and evolution of Galaxies; their morphology and classification; and the examination of active galaxies, and the groups and clusters of galaxies. The latter is important for the understanding of the large-scale structure of the cosmos.

Most galaxies are organized into distinct shapes that allow for classification schemes. They are commonly divided into spiral, elliptical and Irregular galaxies.

As the name suggests, an elliptical galaxy has the cross-sectional shape of an ellipse. The stars move along random orbits with no preferred direction. These galaxies contain little or no interstellar dust; few star-forming regions; and generally older stars. Elliptical galaxies are more commonly found at the core of galactic clusters, and may be formed through mergers of large galaxies.

A spiral galaxy is organized into a flat, rotating disk, usually with a prominent bulge or bar at the center, and trailing bright arms that spiral outward. The arms are dusty regions of star formation where massive young stars produce a blue tint. Spiral galaxies are typically surrounded by a halo of older stars. Both the Milky Way and the Andromeda Galaxy are spiral galaxies.

Irregular galaxies are chaotic in appearance, and are neither spiral nor elliptical. About a quarter of all galaxies are irregular, and the peculiar shapes of such galaxies may be the result of gravitational interaction.

An active galaxy is a formation that is emitting a significant amount of its energy from a source other than stars, dust and gas; and is powered by a compact region at the core, usually thought to be a super-massive black hole that is emitting radiation from in-falling material.

A radio galaxy is an active galaxy that is very luminous in the radio portion of the spectrum, and is emitting immense plumes or lobes of gas. Active galaxies that emit high-energy radiation include Seyfert galaxies, Quasars, and Blazars. Quasars are believed to be the most consistently luminous objects in the known universe.

The large-scale structure of the cosmos is represented by groups and clusters of galaxies. This structure is organized in a hierarchy of groupings, with the largest being the superclusters. The collective matter is formed into filaments and walls, leaving large voids in between.

Cosmology

Cosmology (from the Greek κόσμος “world, universe” and λόγος “word, study”) could be considered the study of the universe as a whole.

Observations of the large-scale structure of the universe, a branch known as physical cosmology, have provided a deep understanding of the formation and evolution of the cosmos. Fundamental to modern cosmology is the well-accepted theory of the big bang, wherein our universe began at a single point in time, and thereafter expanded over the course of 13.7 Gyr to its present condition. The concept of the big bang can be traced back to the discovery of the microwave background radiation in 1965.

In the course of this expansion, the universe underwent several evolutionary stages. In the very early moments, it is theorized that the universe experienced a very rapid cosmic inflation, which homogenized the starting conditions. Thereafter, nucleosynthesis produced the elemental abundance of the early universe. (See also nucleocosmochronology.)

When the first atoms formed, space became transparent to radiation, releasing the energy viewed today as the microwave background radiation. The expanding universe then underwent a Dark Age due to the lack of stellar energy sources.

A hierarchical structure of matter began to form from minute variations in the mass density. Matter accumulated in the densest regions, forming clouds of gas and the earliest stars. These massive stars triggered the reionization process and are believed to have created many of the heavy elements in the early universe which tend to decay back to the lighter elements extending the cycle.

Gravitational aggregations clustered into filaments, leaving voids in the gaps. Gradually, organizations of gas and dust merged to form the first primitive galaxies. Over time, these pulled in more matter, and were often organized into groups and clusters of galaxies, then into larger-scale superclusters.

Fundamental to the structure of the universe is the existence of dark matter and dark energy. These are now thought to be the dominant components, forming 96% of the mass of the universe. For this reason, much effort is expended in trying to understand the physics of these components.

Adapted from the Wikipedia article Astronomy, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Planetary models and observational astronomy

The Eudoxan system had several critical flaws. One was its inability to predict motions exactly. Callippus’ work may have been an attempt to correct this flaw. A related problem is the inability of his models to explain why planets appear to change speed. A third flaw is its inability to explain changes in the brightness of planets as seen from Earth. Because the spheres are concentric, planets will always remain at the same distance from Earth. This problem was pointed out in Antiquity by Autolycus of Pitane (c. 310 BCE).

Apollonius of Perga (c. 262 BC–c. 190 BC) responded by introducing two new mechanisms that allowed a planet to vary its distance and speed: the eccentric deferent and the deferent and epicycle. The deferent is a circle carrying the planet around the Earth. (The word ”deferent” comes from the Latin ”ferro, ferre”, meaning “to carry.”) An eccentric deferent is slightly off-center from Earth. In a deferent and epicycle model, the deferent carries a small circle, the epicycle, which carries the planet. The deferent-and-epicycle model can mimic the eccentric model, as shown by Apollonius’ theorem. It can also explain retrogradation, which happens when planets appear to reverse their motion through the zodiac for a short time. Modern historians of astronomy have determined that Eudoxus’ models could only have approximated retrogradation crudely for some planets, and not at all for others.

In the 2nd century BCE, Hipparchus, aware of the extraordinary ac

Hipparchus also compiled a star catalogue. According to Pliny the Elder, he observed a ”nova” (new star). So that later generations could tell whether other stars came to be, perished, moved, or changed in brightness, he recorded the position and brightness of the stars. Ptolemy mentioned the catalogue in connection with Hipparchus’ discovery of precession. (Precession of the equinoxes is a slow motion of the place of the equinoxes through the zodiac, caused by the shifting of the Earth’s axis). Hipparchus thought it was caused by the motion of the sphere of fixed stars.

Heliocentrism and cosmic scales

In the 3rd century BCE, Aristarchus of Samos proposed an alternate cosmology (arrangement of the universe): a heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe (hence he is sometimes known as the “Greek Copernicus”). His astronomical ideas were not well-received, however, and only a few brief references to them are preserved. We know the name of one follower of Aristarchus: Seleucus of Seleucia.

Aristarchus also wrote a book ”On the Sizes and Distances of the Sun and Moon”, which is his only work to have survived. In this work, he calculated the sizes of the Sun and Moon, as well as their distances from the Earth in Earth radii. Shortly afterwards, Eratosthenes calculated the size of the Earth, providing a value for the Earth radii which could be plugged into Aristarchus’ calculations. Hipparchus wrote another book ”On the Sizes and Distances of the Sun and Moon”, which has not survived. Both Aristarchus and Hipparchus drastically underestimated the distance of the Sun from the Earth.

Adapted from the Wikipedia article Greek astronomy, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Sounding rocket X-ray astronomy involves using a sounding rocket to carry an X-ray detector to high altitudes. The first evidence of X-rays from the Sun and of an astronomical X-ray source from the Milky Way (MW), other than the Sun, was detected by a sounding rocket. These rockets have contributed significantly to our understanding of the Sun, the solar system, and the universe as a whole.

A sounding rocket, sometimes called a research rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The origin of the term comes from nautical vocabulary, it refers to ”sounding”, which means throwing a weighted line off of a ship to gauge the water’s depth, or measuring a vertical distribution of a physical property such as in atmospheric sounding. Here it is intended as taking a measurement.

Sounding rockets have certain advantages even over satellites for X-ray astronomy. They are usually much simpler, have far fewer interfaces to match up, and require launch facilities that are less elaborate. Some basic space research efforts need to successfully explore the region of the atmosphere above balloon altitudes (about 40& km) and below satellite orbits (about 160& km). Convenient to the effort is the informality. For most payloads, only one experimenter is involved so there is no need for formal, time-consuming reviews to ensure compatibility with other experimenters. In addition, there is low cost. Some sounding rockets cost as little as $10,000; then, there is recoverability, geograph

An X-ray detector is placed in the nose cone section of a sounding rocket and launched above the atmosphere. The largest drawback to rocket flights is their very short duration (just a few minutes above the atmosphere before the rocket falls back to Earth) and their limited field of view. A rocket launched from the United States will not be able to see sources in the southern sky; a rocket launched from Australia will not be able to see sources in the northern sky.

Sounding rockets are in use both for detecting and studying X-ray sources, including newly discovered ones, and to develop and perfect novel X-ray astronomy techniques and instruments.

Adapted from the Wikipedia article Sounding rocket X-ray astronomy, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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Galactic astronomy is the study of our own Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies.

Galactic astronomy should not be confused with galaxy formation and evolution, which is the general study of galaxies, their formation, structure, components, dynamics, interactions, and the range of forms they take.

Our own Milky Way galaxy, where our solar system belongs, is in many ways the best studied galaxy, although important parts of it are obscured from view in visible wavelengths by regions of cosmic dust. The development of radio astronomy, infrared astronomy and submillimeter astronomy in the 20th Century allowed the gas and dust of the Milky Way to be mapped for the first time.

Adapted from the Wikipedia article Galactic astronomy, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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solar mass (begin{smallmatrix}M_odotend{smallmatrix}), , is a standard way to express mass in astronomy, used to describe the masses of other stars and galaxies. It is equal to the mass of the Sun, about two nonillion kilograms or about 332,950 times the mass of the Earth or 1,048 times the mass of Jupiter.

:M_{odot}=( 1.98892 pm 0.00025 ) times10^{30}hbox{ kg}

The solar mass can be determined from the length of the year, the distance of the Earth to the Sun (the astronomical unit) (AU), and the gravitational constant (”G”) as

:M_odot=frac{4 pi^2 times ({Gtimes(.

The value of the gravitational constant was derived from 1798 measurements by Henry Cavendish using a torsion balance. The value obtained differed only by about 1% from the modern value. The diurnal parallax of the Sun was accurately measured during the transits of Venus in 1761 and 1769, yielding a value of 9″ (compared to the present 1976 value of 8.794148″). When the value of the diurnal parallax is known, the distance to the Sun can be determined from the geometry of the Earth.

The first person to estimate the mass of the Sun was Isaac Newton. In his work ”Principia”, he estimated that the ratio of the mass of the Earth to the Sun was about 1/28,700. Later he determined that this value was based upon a faulty value for the solar parallax, which was used to estimate the distance to the Sun (1 AU). He revised his result to obtain a ratio of 1/169,282 in the third edition of the ”Principia”. The current value for the solar parallax is sm

Until recently, neither the AU nor the gravitational constant was precisely measured. However, a determination of the relative mass of another planet in the Solar System or of a binary star in units of solar masses does not depend on these poorly known constants. So it was useful to express these masses in units of solar masses (see Gaussian gravitational constant).

The mass of the Sun changes slowly, compared to the lifetime of the Sun. Mass is lost due to two main processes in nearly equal amounts. First, in the Sun’s core hydrogen is converted into helium by nuclear fusion, in particular the pp chain. Thereby mass is converted to energy in correspondence to the mass–energy equivalence. This energy is eventually radiated away by the Sun. The second process is the solar wind, which is the ejection of mainly protons and electrons to outer space.

Adapted from the Wikipedia article Solar mass, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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He started working at Texas Instruments in 1961, where one of his early projects was the development of a low-temperature thermometer that was developed using a germanium semiconductor that had been doped with small quantities of gallium, which measured changes in temperature based on the change in the device’s electrical resistance as energy was absorbed. Based on his academic experiences, he came to the conclusion that the technology behind this thermometer could be integrated as the basis for a bolometer that could be used to measure the radiant energy coming from stars as infrared radiation, waves that occupy a portion of the electromagnetic spectrum whose wavelength is longer than for visible light (400-700& nm), but shorter than those of terahertz radiation (100& µm – 1& mm) or microwaves.

Astronomers had been trying to find measures to detect infrared radiation for years, and Low went to the National Radio Astronomy Observatory in Green Bank, West Virginia in 1962 to test his bolometer, more sensitive to infrared than detectors previously in use on the Green Bank Telescope, the world’s largest fully steerable radio telescope. However, infrared waves are absorbed by molecules such as water vapor in the atmosphere.

To avoid atmospheric absorption of infrared radiation, Low developed devices that could be placed aboard aircraft, first using a Douglas A-3 Skywarrior from the United States Navy that carried a 2-inch telescope in 1965 and 1966, and later using a Learjet operated by NASA with a 12-inch telescope on board. Low used the Learjet to

He had worked at Rice University and at the University of Arizona. He was also the president of Infrared Laboratories, Inc., which he founded in 1967 to make infrared detectors and cryostats for observatories and infrared microscopes as well.

He proposed and joined the international project to build the Infrared Astronomy Satellite (IRAS), a project that included joint efforts from the United States, United Kingdom and the Netherlands, which made the first survey of the infrared sky from space, avoiding all atmospheric interference with observations, starting in 1983. Low served as the chief technologist for the project. After an accident at Jet Propulsion Laboratory destroyed preamplifiers used in the infrared detectors, Low led an effort at Infrared Laboratories to develop improved replacement units to resolve the crisis. IRAS was able to discover in excess of 500,000 infrared sources, including many galaxies, and has discovered shells of debris surrounding stars that show the early stages of planetary formation, with debris similar to that later found as the Kuiper belt that encircles our Solar System beyond the orbit of Neptune. Based on these findings, researchers have concluded that the majority of galactic radiation is emitted in the form of infrared radiation that is generated when light from young stars is absorbed by interstellar dust and then radiated from the dust in the form of heat. In 1984, IRAS found that the galaxy Arp 220, located 300 million light years from Earth, is the closest Ultraluminous Infrared Galaxy, emitting 100 times more energy than the Milky Way galaxy, primarily in the infrared spectrum, even though it is faintly visible by telescope using visible light.

Low was named to serve as facility scientist for NASA’s Space Infrared Telescope Facility, later renamed the Spitzer Space Telescope. The effort had been delayed by cost overruns, until Low had an inspiration at a 1993 retreat for the project’s scientists; Rather than place the entire telescope in a bath of liquid helium to cool the unit to temperatures near absolute zero, the unit could be exposed to the vacuum of space to radiate most of its heat while the detectors themselves were the only components cooled using liquid helium, a design change that allowed the Spitzer project to go ahead towards its launch in 2003. Low’s design has also been included in other space probes, such as the James Webb Space Telescope, a partial successor to the Hubble Space Telescope that will search for the oldest objects in the universe.

Adapted from the Wikipedia article Frank J. Low, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki

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