B CLASS – Subclass of C-type asteroids with higher albedo than average C type.
BADDELEYITE – Zirconium oxide, ZrO2, found in some lunar and martian meteorites.
BACKSCATTERING – Primary radiation or particles (electrons, protons, etc.) deflected or secondary radiation and particles emitted in the general direction of the incident beam.
BACKSCATTERED ELECTRON – High energy primary electron that suffers large angle (> 90°) scattering and re-emerges from the entry surface of a specimen. Backscattered electrons usually have energies close to that of the primary electron beam. They are valuable in microanalysis because their number depends on the average atomic number of the sample.
Compositional variations (variations in average Z) can be imaged by mapping backscattered electron intensities. The image above shows white magnetite (avg. Z~21); light gray olivine (avg. Z~15), gray glass (avg. Z~13), and black plagioclase (avg. Z~11).
BALL AND STICK MODEL – One way to represent molecules, in which each atom is represented by a ball, and each bond between atoms by a stick. The sizes of the balls have no relationship to the actual ionic or atomic radii. Although the atoms are also proportionally too small compared to the bond lengths, the bonding pattern is clearly visible. In the case of minerals and other periodic solids, only part of the structure may be shown.
BALLEN STRUCTURE – Microscopic shock-deformation feature in quartz. Oval quartz with rims of tiny vugs filled with amorphous material.
BALLISTIC SEDIMENTATION – Emplacement of ballistically transported impact ejecta, and ejecta-surface interaction.
BALMER SERIES – Hydrogen series of emission that results when an electron drops into the second orbital. Four of the lines are in the visible spectrum, and the remainder is in the ultraviolet.
BAND – Continuous range of allowed energies for electrons in a solid. Individual atoms can have only certain quantized energies. As atoms bond to form solids, each energy level widens to accommodate the shifted levels of adjacent atoms. Atoms in the solid can occupy any energy in one of the newly-formed bands.
BAND GAP – Range of energies between two allowed energy bands in a solid. Electrons in the solid may not adopt states which have energies in the band gap. Note however that doping a semiconductor to make it extrinsic produces extra states which may lie in the band gap. Metals generally have no apparent band gap, although there may be gaps between the bands in any one direction in the crystal. Semiconductors (semimetals) have 0-2 eV band gaps. Insulators (nonmetals) have band gaps greater than ~2 eV. We are typically interested in the band gap falling between the conduction bands and valence bands in semiconductors.
BAR – Unit of pressure equal to 100 kPa.
BARN – Unit of area equal to equal to 10-24 cm2.
BARRED GALAXY – Galaxy with a bright central bar of stars.
BARRINGER CRATER – Best known and best preserved impact crater on Earth; named after Daniel Barringer and still owned by his family; also known as Meteor Crater, Coon Butte, and Canyon Diablo (see http://www.barringercrater.com/). Measuring 1.2 km across and 175 m deep, with a rim 45 m higher on average than the surrounding plain, it lies 55 km east of Flagstaff, Arizona, at 35° 02' N, 111° 01' W. It was formed ~50,000 years ago by the impact of an iron meteorite ~50 m across and weighing several hundred thousand tons. Most of the meteorite vaporized or melted upon impact, leaving only numerous, mostly small fragments of octahedrite, scattered up to 7 km from the impact site. Only ~30 tons, including a 693-kg sample, are known to have been recovered.
BARRINGERITE – Nickel-iron phosphide, (Fe,Ni)2P, found in iron meteorites.
BARYCENTER – The center of mass of a system of bodies, e.g., the center of mass of the solar system or between two mutually orbiting bodies (Earth-Moon, Sun-Jupiter, or two stars).
BARYON – Fermionic hadron composed of three quarks, which is acted on by the strong nuclear force. Baryons include the nucleons (protons and neutrons) and a variety of heavier, but short-lived, particles called hyperons. There are ~120 types of baryons. Baryons account for more than 99.5% of the total mass of all the chemical elements in the universe. Matter that is composed of baryons is known as "baryonic matter".
BARYON DECAY – Prediction of several grand-unified theories (GUTs) that baryons are not ultimately stable but indeed decay. Present theory and experimentation demonstrate that if protons are in fact unstable, they decay with a halflife of at least ~1034 y.
BARYON NUMBER CONSERVATION – Principle that the total number of baryons must remain the same in any nuclear reaction.
BASALT – Fine-grained, dark-colored rock of volcanic origin composed of approximately equalk amounts of plagioclase feldspar and clinopyroxene, with smaller amounts of other minerals usually including olivine and magnetite. Basalt magma contains less than ~52 wt. % SiO2 (silica) and has low viscosity (resistance to flow). Basalt is the most common extrusive igneous rock on the terrestrial planets, and the term is applied to most low viscosity dark silicate lavas, regardless of composition..
BAYER NAME – Combination of a Greek letter and the name of a constellation (α Centauri, ε Orionis etc.) used to identify bright stars. The system was first used by Johann Bayer in 1603. Brighter stars in a constellation usually have a letter near the beginning of the alphabet, and dimmer stars usually have a letter nearer the end of the alphabet. A few faint stars were given lower-case Roman letters from a to z or upper-case Roman letters from A to Q (p Eridani, N Velorum etc.)
BCS THEORY – Theory proposed to explain both superconductivity and superfluidity. It proposes that in the superconducting (or superfluid) state electrons form pairs, where two electrons act as a single unit. It takes a nonzero amount of energy to break such pairs, and imperfections in the superconducting solid, which would normally lead to resistance, are incapable of breaking the pairs, so no dissipation occurs and there is no resistance.
BEAM – Unidirectional or approximately unidirectional flow of electromagnetic radiation or particles (electrons, protons, ions, etc.).
BEQUEREL – Unit of radioactivity, equal to one disintegration per second.
BETA DECAY – Nuclear decays which proceed via the weak interaction are beta (β) decays. These include all nuclear decays in which the atomic mass (A) remains constant and the atomic number, Z, changes by one unit. Examples of β decay processes include:
The most elementary β decay process is free neutron decay:
"Beta" originally referred to electrons, but β decays can involve electrons or positrons, and either electron neutrinos or antineutrinos.
BIG BANG – Beginning point of time and space for the universe. A state of extremely high (classically, infinite) density and temperature from which the universe began expanding.
BIG BANG NUCLEOSYNTHESIS – Formation of elements in the Big Bang. Calculated abundances of these isotopes (D (deuterium = 2H), 3H, 3He, 4He, 6Li, 7Li, and 7Be) and of protons (1H) and neutrons (n) vs. time are shown in the diagram. Note that the mass fraction scale is logarithmic and very little Li and Be were formed. All heavier elements were formed in stars.
Using the observed abundances of early formed elements and isotopes, it is possible to estimate the overall density of the universe The boxes and arrows show the observed values for the isotopes indicated; the cyan band is the best estimate of baryon density using these data.
BINDING ENERGY1 – Amount of energy released at the creation of a particular isotope. Protons and neutron are held together by the "strong force". The strong force only acts over very small distances but is able to overcome the electrostatic repulsion between protons. The magnitude of the bonding is measured by the binding energy per nucleon where "nucleon" is a collective name for neutrons and protons (sometimes called the "mass defect per nucleon"). The mass defect reflects the fact that the total mass of the nucleus is less than the sum of the mass of the individual neutrons and protons that formed it. The difference in mass is equivalent to the energy released in forming the nucleus. The general decrease in binding energy beyond iron is caused by the fact that, as the nucleus gets bigger, the ability of the strong force to counteract the electrostatic force between the protons becomes weaker. The most tightly bound isotopes are 62Ni, 58Fe, and 56Fe, which have binding energies of 8.8 MeV per nucleon. Elements heavier than these isotopes can yield energy by nuclear fission; lighter isotopes can yield energy by fusion.
BINDING ENERGY2 – Energy required to remove a particular electron from an atom to an infinite distance.
BIOMASS – Complete dry weight of organic material found in the biosphere.
BIOSPHERE – Volume including the lower part of the troposphere (as high as living organisms can fly or be lofted) and the surface of the earth (including the oceans and uppermost crust), encompassing all the living matter of the earth.
BIREFRINGENCE – Property of a mineral if a ray of light passing through it experiences two refractive indices. The effect is to change the polarization state of the transmitted light. The extent of the change depends on the material and the thickness of the specimen. Birefringence can be induced in some materials by the presence of an applied or residual stress.
BLACKBODY – Ideal object that is a perfect absorber of light and also a perfect emitter of light. A perfect black body will absorb all radiation that falls on it, and will emit radiation that has a continuous spectrum determined only by the temperature of the black body:
Where, T is the temperature (K), λ = wavelength (cm), c = speed of light, k = Boltzmann's constant (1.37 x 10-18 erg/K), and h = Planck's constant (6.626 x 10-27 erg sec).
Light is emitted by solid objects because they are composed of atoms and molecules which can emit and absorb light. They emit light because they are vibrating due to their heat content (thermal energy). The distribution of energy radiated against wavelength follows the Planck curve and, for a given temperature, there is a particular wavelength at which the maximum emission takes place specified by Wien’s Law. Stars and hot solid bodies are not perfect black bodies, but their radiation can be described in terms of black-body properties.
BLACK HOLE – Maximally gravitationally collapsed object predicted to exist by the theory of general relativity, from which no material object, light or signal of any kind can escape. Many black holes form when a high mass supergiant star explodes in a supernova explosion at the end of its life. A star probably must have a mass of >40 Msun to leave a ~3 Msun black hole. Black holes are detected by the effects they have on neighboring stars. The centers of most galaxies, including our own, contain super-massive black holes which have sucked in thousands of stars.
BLACK-HOLE DYNAMIC LAWS – Laws describing the interaction of black holes and their surroundings. The first law of black hole dynamics states that the conservation laws of mass-energy, electric charge, linear momentum, and angular momentum, hold for interactions between black holes and normal matter. This is analogous to the first 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 during black-hole interactions, or interactions between black holes and normal matter. This is analogous to the second law of thermodynamics, with the surface areas of the black holes being a measure of the entropy of the system.
BL LAC OBJECT – Active galaxy characterized by very rapid (day to day) variability in total luminosity, no emission lines, strong nonthermal radiation, and starlike appearance. It is apparently a radio galaxy aligned so that we are looking down the jet into the nucleus.
BLUE APPARENT MAGNITUDE – Apparent magnitude of a star or galaxy when viewed through a blue filter. This magnitude is commonly used for nearby galaxies because, historically, pictures of galaxies were photographed with plates sensitive to blue light.
BODE'S LAW – Also called the Titus-Bode Law, this relationship for planetary distances from Sun was discovered by Titus in 1766 and developed further by Bode in 1772. Start with the series 0, 3, 6, 12, 24... , add 4 to each number, and divide by 10. The resulting values correspond to distances from the Sun for the planets and asteroid belt. This relationship works out to Uranus, but fails for Neptune and beyond. A similar relationship is observed for the moons of the gas giant planets (distances measured from planet).
BODY-CENTERED CUBIC (BCC) PACKING – Way in which atoms or ions (considered as hard spheres) pack together to fill space. In BCC packing, the spheres in layer a are separated slightly and the spheres in layer b are offset so that they fit into the depressions between atoms in layer a. Each sphere is touched by eight neighbors, four in the layer below and four in the layer above.
BOHR RADIUS – Radius of the n = 1 orbital in hydrogen; equal to 0.529 × 10-10 m.
BOILING POINT – Temperature at which the vapor pressure of a liquid is equal to the ambient pressure; thus, the boiling point depends on pressure. A liquid may change to a gas at temperatures below the boiling point by evaporation. However, evaporation is a surface phenomenon; only molecules located near the gas/liquid surface may evaporate. Boiling is a bulk process; at the boiling point molecules anywhere in the liquid may be vaporized, resulting in the formation of vapor bubbles.
BOLOMETRIC MAGNITUDE – Magnitude of a celestial object corrected to take account of the radiation in parts of the spectrum other than the visible.
BOLTZMANN CONSTANT (σ) – Constant converting the temperature of a gas (K) into the kinetic energy (in Joules or electronvolts) associated with the thermal motion of the particles comprising the gas. It has the numerical value of 1.380 x 10-23 J/K (8.62 x 10-5 eV/K).
BOND – Mechanism by which two (or more) atoms are held together. The mechanism is always reliant on some electron process. Bonds can be divided into two types: valence related (covalen bond, ionic bond, metallic bond) and bonds not involving valence electrons (hydrogen bond and van der Waals bond).
BOND DISSOCIATION ENERGY – Amount of energy required to break a bond between two atoms. Higher bond dissociation energies correspond to stronger bonds.
BOND VIBRATION – Oscillatory motion of two bonded atoms relative to each other. This motion involves two bonded atoms stretching passed their equilibrium position, returning to their equilibrium position, and finally contracting passed their equilibrium position.
BOOMERANG – Millimeter-wavelength telescope and bolometric receiver system designed for long-duration balloon flights from Antarctica. The instrument is being used to measure the angular power spectrum of the CMB at degree and subdegree scales. See http://cmb.phys.cwru.edu/boomerang/ for more information.
BORN REPULSION – Force produced when electron shells of ions begin to overlap. The force is proportional to the spacing between ions, d; number of filled electron shells, n:
BOSON – Particle that transmits a fundamental force. The word "boson" applies to any particle or atomic nucleus that has an integral spin (expressed in units of h/2π). Bosons are not constrained by the Pauli exclusion principle. Photons convey the electromagnetic force between charged particles. Intermediate vector bosons (W and Z particles) transmit the weak nuclear force, which governs the radioactive decay of atomic nuclei. Gluons carry the strong nuclear force between quarks, some of which "leaks" to provide forces between neuclons. The existence of an equivalent force carrier for gravitational force, the graviton, is unproven. The photon and purported graviton have zero mass and charge. W particles have masses of 83 GeV, the W+ has a charge of +1 (in units of the charge on the electron) and the W-, a charge of -1. The electrically neutral Z particles have masses of 93 GeV. Gluons have zero mass and charge but carry another property, analogous in some respects to electrical charge, which is called 'color'.
The lifetime of a force-carrying particle is inversely proportional to the energy that is required to make it. Thus, the range over which a gauge boson can transmit a force is inversely proportional to its mass. The photon and hypothesized graviton have zero mass and can transmit the electromagnetic and gravitational forces over infinite distances. The heavy W and Z particles have lifetimes of ~10-25 s, so weak interaction is restricted to ~10-17 m. Although gluons have zero mass, and might therefore be expected to have infinite range, their 'color' properties confine their range of influence to within the diameter of the proton. The strong nuclear force between the protons and neutrons in an atomic nucleus is conveyed by pions (particles composed of quark-antiquark pairs).
BOTTOM-UP STRUCTURE FORMATION – Hypothesis that small structures, perhaps galaxies or even smaller substructures, form first in the universe, followed later by larger structures such as galactic clusters.
BOULE – Large, cylindrical, single crystal of semiconductor material pulled from the melt which is cut into semiconductor wafers.
BOUND STATE – Electrons are considered in a bound state of an atom (or of a solid) when they lack the energy to leave the vicinity of the atom (or solid). The lower the energy of the electron, the more "tightly" bound it is and the less likely it is to take part in interactions with electrons of other atoms or to stray from the atom to which it is bound. Valence band electrons are more tightly bound than conduction band electrons.
BRACHINITE (BRA) – Small subgroup of primitive achondrites, named for the Brachina meteorite that was found in Australia in 1974. Originally, the olivine-rich Brachina was thought to be a second chassignite - a Mars meteorite that contains primarily olivine. However, further research showed Brachina has a distinct trace-element pattern and unique oxygen isotopic composition. With only a handful of known representatives, brachinites are composed mainly of small, equigranular grains of olivine (Fa30-35), with small amounts of scattered clinopyroxene, and plagioclase (An22-32). Recent studies of the olivine compositions of different asteroids suggest that 289 Nenetta may be the parent body of this group.
BRAGG'S LAW – Relationship derived by the English physicists Sir W.H. Bragg and his son Sir W.L. Bragg in 1913 to explain how crystals diffract X-ray beams at specific angles of incidence (θ):
The variable d is the distance between atomic layers in a crystal, and the variable lambda l is the wavelength of the incident X-ray beam, n is an integer.
BRAVAIS LATTICE – One of fourteen possible arrays of points repeated periodically in three-dimensional space such that the arrangement of points about any one of the points is identical in every respect to that about any other point in the array.
BREAKOUT BUBBLE – Galactic feature produced when hot young stars and supernovae punch holes or blow bubbles in the surrounding gas, and the diffuse hot component escapes the disk into the galactic halo through buoyancy. In fact, there are spectacular examples of bubbles seen at 21 cm in the Galactic interstellar medium. The image below is of a large Galactic HI supershell (white region at center). The empty supershell has a central brightness temperature of about 3~K; the shell edges have a brightness temperature around 60~K (black). The shell also shows narrow channels which appear to extend to the Galactic halo, forming a "chimney" above and below the plane. The shell lies at a distance of about 6.5 kpc, has a diameter of roughly 600 pc and extends more than 1.1 kpc above the Galactic plane.
BRECCIA – Clastic sedimentary rock composed of angular clasts in a consolidated matrix. Breccias can be produced in several geologic processes: impact breccia, tectonic breccia, volcanic breccia (eruption breccia, vent breccia), sedimentary breccia (e.g., rock fall breccia), collapse breccia (e.g., in karst areas). Depending on the origin of the clasts, monomict (monogenetic, monolithologic) and polymict (polygenetic, polylithologic) breccias may be distinguished.
BREMSSTRAHLUNG – X-rays produced when fast electrons pass through matter. Bremsstrahlung (German for "slowing-down radiation") energy varies continuously from 0 up to the energy of the incident electron.
BROWN DWARF – Low-mass substellar object near the minimum mass for hydrogen burning to occur in its core, which is ~0.084 MSun. Brown dwarfs heavier than 13 Jupiter masses do fuse deuterium. They have fully convective surfaces and interiors with no chemical differentiation by depth. Lithium is generally present in brown dwarfs and not in low-mass stars and may be used to distinguish candidate brown dwarfs from low-mass stars. Brown dwarf objects are a possible source of baryonic dark matter. Brown dwarfs are possible dark matter halo objects.
BROWNIAN MOTION – Continuous random motion of solid microscopic particles when suspended in a fluid medium due to continuous bombardment by atoms and molecules.
BUCKMINSTERFULLERENE – One of many naturally occurring forms of carbon called fullerenes. Buckminsterfullerene (the structure of which is informally known as a "buckyball") is made of 60 carbon atoms (C60). The fullerene molecular structures resemble the geodesic domes once designed by Buckminster Fuller. Fullerenes can survive impacts and retain encapsulate interstellar atoms like N, He, or Ar.
BURGERS VECTOR – Crystal vector which denotes the amount and direction of atomic displacement which will occur within a crystal when dislocation moves.