Dictionary of Astrophysics
By Students’ Academy
Copyright@2011Students’ Academy
Smashwords Edition
Chapter 1
A
Accretion
Accretion refers to the formation of a celestial object by the effect of gravity pulling together surrounding objects and gases
In other words it is defined as the coming together of the dust and gas into larger bodies such as stars, planets and moons.
AAS
Full form of AAS is the American Astronomical Society.
Active Galactic Nuclei
Active Galactic Nuclei comes in to existence through the production of enormous amounts of energy at all wavelengths of the electromagnetic spectrum by normal galaxies with a massive black hole accreting gas at its center.
Angstrom
Angstrom is a unit of length which is equal to 0.00000001 centimeters. Scientifically it is also written as 1 × 10-8 cm.
Anonymous FTP
Anonymous FTP is a practice in which users are allowed to log in as 'guest' without a password and copy whatever has been made available.
Apastron
Apastron refers to the point of greatest separation of two stars, as in a binary star orbit.
Aphelion
Apoapsis refers to a point in solar orbit; it is the point in the orbit of a planet or comet that is at the greatest distance from the sun
Apogee
Apogee refers to a point in its orbit where an Earth satellite is farthest from the Earth.
Ariel V
Ariel V also known as UK-5. It refers to a UK X-ray mission.
ASCA
ASCA means the Japanese Asuka spacecraft It was formerly known as ASTRO-D.
ASM
Full form of ASM is All Sky Monitor. ASM detectors are carried by many high-energy satellites, including the ASM on Vela 5B, Ariel V, and the Rossi X-ray Timing Explorer.
Astronomical Unit (AU)
Astronomical Unit is the unit of length used for distances within the solar system; equal to the mean distance between the Earth and the Sun (approximately 93 million miles or 150 million kilometres).
Astrochemistry
Astrochemistry is the branch of Chemistry that studies chemical interactions between the gases and dust interspersed between the stars.
Atomic Gas
Atomic gas refers to the gas which is composed of individual atoms (such as hydrogen or carbon) that are not bound to each other as molecules. Atomic gas may be ionized or mixed with molecular gas.
Chapter 2
B
Balmer Lines
Balmer Lines refers to the emission or absorption line in the spectrum of hydrogen that arise from transitions between the second (or first excited) state and higher energy states of the hydrogen atom.
Balmer Series
Balmer Series refers to an equation which provides the description of the emission spectrum of hydrogen when an electron is jumping to the second orbital. Four of the lines are in the visible spectrum; the remainder is in the ultraviolet.
BBXRT
Full form of BBXRT is Broad Band X-Ray Telescope on ASTRO-1 shuttle flight (Dec. 1990)
Binary Star
Binary Star is a system of two stars that revolve around each other under their mutual gravitation
Black Hole
Black Hole refers to an object in the outer space whose gravity is so strong that not even light can escape from it.
Black-Hole Dynamic Laws
At present there are two laws of black hole dynamics.
First Law
The first law of Black hole dynamics is almost similar to the first law of thermodynamics. The first law of black hole dynamics states that, the conservation laws of mass-energy, electric charge, linear momentum, and angular momentum, work together for interactions between black holes and normal matter.
Second Law
The second law of black hole dynamics is almost similar to the second law of thermodynamics. The second law of black hole dynamics states that the sum of the surface areas of all black holes involved can never decrease, with black-hole interactions, or interactions between black holes and normal matter,
Blackbody Radiation
Blackbody Radiation refers to the radiation which is produced by a blackbody; it is the radiation at particular frequencies all across the spectrum.
Blackbody Temperature
Blackbody Temperature refers to the temperature of an object if it is re-radiating all the thermal energy that has been added to it.
Boltzmann Constant
Boltzmann Constant refers to that particular constant which provides the description of the relationship between temperature and kinetic energy for molecules in an ideal gas. It is equal to 1.380622 × 10-23 J/K.
Brahe, Tycho 1546-1601
Brahe Tycho was a Dnish astronomer whose accurate astronomical observations formed the basis for Johannes Kepler's laws of planetary motion.
Browse
Browse refers to the HEASARC's user interface/data browser
Chapter 3
C
Calibration
Calibration refers to the minute and careful act of checking or adjusting (by comparison with a standard) the accuracy of a measuring instrument
Calibration refers to a reprocess for translating the signals produced by a measuring instrument (such as a telescope) into something that is scientifically useful.
Cepheid
Cepheid refers to a pulsating variable star. The stars of these types experience a rhythmic pulsation as indicated by its regular pattern of changing brightness as a function of time.
CGRO
Full form of CGRO is Compton Gamma Ray Observatory
Chandrasekhar Limit (S. Chandrasekhar; 1930)
Chandrasekhar Limit is named after the famous scientist S. Chandrasekhar; Chandrasekhar Limit A limit mandates that no white dwarf (a collapsed, degenerate star) can be more massive than about 1.4 solar masses. Any degenerate object more massive must inevitably collapse into a neutron star.
Cluster of Galaxies
Cluster of Galaxies refers to a system of galaxies containing from a few to a few thousand member galaxies which are all gravitationally bound to each other.
Collecting Area
Collecting Area refers to the amount of area a telescope has that is capable of collecting electromagnetic radiation.
Compton Effect (A.H. Compton; 1923)
Compton Effect is named after the famous scientist A. H. Compton. Compton Effect presents the demonstration that photons (the quantum of electromagnetic radiation) have momentum. A photon fired at a stationary particle, such as an electron, will impart momentum to the electron and, since its energy has been decreased, will experience a corresponding decrease in frequency.
Copernicus
Copernicus is also known as OAO-3. It is NASA ultraviolet/X-ray mission.
Copernicus, Nicolaus 1473-1543
Nicolaus Copernicus was a Polish astronomer; he was responsible for advancing the heliocentric theory that the Earth and other planets revolve around the Sun. This was highly controversial at the time as the Ptolemaic view of the universe, which was the prevailing theory for over 1000 years, was deeply ingrained in the prevailing philosophy and religion. (It should be noted, however, that the heliocentric idea was first put forth by Aristarcus of Samos in the 3rd century BC, a fact known to Copernicus but long ignored.)
Corona
Corona refers to the uppermost level of the solar atmosphere, characterized by low densities and high temperatures (> 1,000,000 degrees K).
Cosmic Background Radiation
Cosmic Background Radiation refers to the background of radiation mostly in the frequency range 3 × 108 to 3 × 1011 Hz ; it was discovered in space in 1965. It is believed to have been left after the Big Bang.
Cosmic Ray
Cosmic Ray refers to a very highly penetrating ionizing radiation of extraterrestrial origin; consisting chiefly of protons and alpha particles; collision with atmospheric particles results in rays and particles of many kinds.
Cosmological Constant; Lambda
Cosmological Constant or Lambda refers to a constant which is introduced to the Einstein field equation, intended to admit static cosmological solutions. At the time the current philosophical view was the steady-state model of the Universe, where the Universe has been around for infinite time.
G + Lambda g = 8 pi T.
G + Lambda g = 8 pi T. refers to a scientific equation. According to Hubble's later discovery the introduction of the cosmological constant was unnecessary. It reveals a new thought: if Einstein had believed what his field equation was telling him, he could have claimed the expansion of the Universe as perhaps the greatest and most convincing prediction of general relativity. According to Albert Einstein it was the greatest blunder of his life.]
Cosmological Distance
Cosmological Distance refers to a distance extremely away from the boundaries of our Galaxy. When viewing objects at cosmological distances, the curved nature of spacetime could become apparent. Possible cosmological effects include time dilation and red shift.
Cosmological Redshift
Cosmological Redshift refers to an effect where light emitted from a distant source appears redshifted because of the expansion of spacetime itself. Compare Doppler Effect.
Chapter 4
D
De Broglie Wavelength (L. de Broglie; 1924)
De Broglie Wavelength is named after the famous scientist L. de Broglie. This Wavelength predicts that particles also have wave characteristics, where the effective wavelength of a particle would be inversely proportional to its momentum; the constant of proportionality is the Planck constant.
Declination
Declination refers to a coordinate which, along with right ascension, may be used to locate any position in the sky. Declination is analogous to latitude for locating positions on the Earth.
Deconvolution
Deconvolution refers to a technique of image processing; this process removes features in an image that are caused by the telescope itself rather than from actual light coming from the sky.
Density
Density denotes the amount per unit size; it is measured in grams per cubic centimeter (or kilograms per liter); the density of water is 1.0; iron is 7.9; lead is 11.3.
Disk
In Astrophysics, Disc refers to the visible surface of the Sun (or any heavenly body) projected against the sky.