X-ray Astronomy

stars emit a variety of electromagnetic radiation including X-rays, but this is unable to penetrate the Earth's atmosphere to be detected. Very hot stars send out large amounts of X-rays which can be detected by equipment contained on space satellites. The satellite ROSAT launched in 1990 has equipment to undertake X-ray astronomy and obtain information about distant bodies in space (e.g. WHITE DWARFS and SUPERNOVAE) that are emitting X-rays.

Taken from Dictionary of Science

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X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray emission from celestial objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray astronomy is part of space science.

X-ray emission is expected in sources which contain an extremely hot gas at temperatures from a million to hundred million degrees kelvin. In general, this occurs in objects where the atoms and/or electrons have a very high energy. The discovery of the first cosmic X-ray source in 1962 came as a surprise. This source is called Scorpius X-1, the first X-ray source found in the constellation Scorpius. Based on discoveries in this new field, Riccardo Giacconi received the Nobel Prize in Physics in 2002. It was found that the X-ray emission of Sco X-1 was 10,000 times greater than its optical emission, based on a precise location obtained with a modulation collimator - a specific type of coded aperture imager. In addition, the energy output in X-rays is 100,000 times greater than the total emission of the Sun in all wavelengths. It is now known that such X-ray sources are compact stars, such as neutron stars and black holes. The energy source is gravity. Gas is heated by the fall in the strong gravitational field of celestial objects.

Many thousands of X-ray sources are known. In addition, it appears that the space between galaxies in a cluster of galaxies is filled with a very hot, but very dilute gas at a temperature between 10 and 100 megakelvin (MK). The total amount of hot gas is five to ten times the total mass in the visible galaxies.

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Ultraviolet Radiation

a form of radiation that occurs beyond the violet end of the visible light spectrum of ELECTROMAGNETIC WAVES. Ultraviolet rays have a FREQUENCY ranging from 10¹⁵Hz to 10¹⁸Hz, with a wavelength from 10^-7m to 10^-10m. They are part of natural sunlight and are also emitted by white-hot objects (as opposed to red-hot objects, which emit INFRARED RADIATION). As well as affecting photographic film and causing certain minerals to fluoresce, ultraviolet radiation will rapidly destroy bacteria. Although ultraviolet rays in sunlight will convert steroids in human skin to vitamin D (essential for healthy bone growth), too much can cause irreversible damage to the skin and eyes and damage the structure of the DNA in cells. Fortunately, a great deal of the ultraviolet radiation from the sun is prevented from reaching the earth as the OZONE LAYER in the upper atmosphere acts as a UV filter.

Taken from Dictionary of Science

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The discovery of UV radiation was intimately associated with the observation that silver salts darken when exposed to sunlight. In 1801 the German physicist Johann Wilhelm Ritter made the hallmark observation that invisible rays just beyond the violet end of the visible spectrum were especially effective at darkening silver chloride-soaked paper. He called them "de-oxidizing rays" to emphasize their chemical reactivity and to distinguish them from "heat rays" at the other end of the visible spectrum. The simpler term "chemical rays" was adopted shortly thereafter, and it remained popular throughout the 19th century. The terms chemical and heat rays were eventually dropped in favor of ultraviolet and infrared radiation, respectively.

The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is strongly absorbed by air, was made in 1893 by the German physicist Victor Schumann.

Taken from Wikipedia

Quantum

(plural quanta) a small amount or unit of electromagnetic radiation which can be thought of as a particle of energy.

Taken from Dictionary of Science

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In physics, a quantum (plural: quanta) is the minimum unit of any physical entity involved in an interaction. An example of an entity that is quantized is the energy transfer of elementary particles of matter (called fermions) and of photons and other bosons. The word comes from the Latin "quantus", for "how much." Behind this, one finds the fundamental notion that a physical property may be "quantized", referred to as "quantization". This means that the magnitude can take on only certain discrete numerical values, rather than any value, at least within a range. There is a related term of quantum number.

A photon, for example, is a single quantum of light, and may thus be referred to as a "light quantum". The energy of an electron bound to an atom (at rest) is said to be quantized, which results in the stability of atoms, and of matter in general.

As incorporated into the theory of quantum mechanics, this is regarded by physicists as part of the fundamental framework for understanding and describing nature at the infinitesimal level, for the very practical reason that it works. It is "in the nature of things", not a more or less arbitrary human preference.

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Radiation

the giving out of energy from a source, which may be in the form of ELECTROMAGNETIC WAVES (radio, light, X-rays, infrared rays, etc.), particles or sound waves.

Taken from Dictionary of Science

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In physics, radiation describes any process in which energy emitted by one body travels through a medium or through space, ultimately to be absorbed by another body. Non-physicists often associate the word with ionizing radiation (e.g., as occurring in nuclear weapons, nuclear reactors, and radioactive substances), but it can also refer to electromagnetic radiation (i.e., radio waves, infrared light, visible light, ultraviolet light, and X-rays) which can also be ionizing radiation, to acoustic radiation, or to other more obscure processes. What makes it radiation is that the energy radiates (i.e., it travels outward in straight lines in all directions) from the source. This geometry naturally leads to a system of measurements and physical units that are equally applicable to all types of radiation. Some radiations can be hazardous.

Taken from Wikipedia