The Babinet point typically lies only 15° to 20° above the sun, and hence is difficult to observe because of solar glare. The existence of this neutral point was discovered by Babinet in 1840.
2. In receivers, the noise in the absence of signal modulation on the carrier.
Ambient noise detected, measured, or recorded with the signal part of the background noise. Included in this definition is the interference resulting from primary power supplies, that separately is commonly described as hum.
2. A redundant component in a system which is not the normally active (or prime, primary) component. Also known as second-string.
Atmospheric backward scatter depletes 6 to 9 percent of the incident solar beam before it reaches the earth's surface.
In radar usage, backward scatter refers only to that radiation scattered at 180° to the direction of the incident wave.
2. A weight that counterbalances something, especially on an aircraft control surface, a weight installed forward of the hinge axis to counterbalance the surface aft of the hinge axis.
It has been suggested that ball lightning is a temporarily stable plasma.
A rocket with a self-contained propulsion unit is not considered a ballistic body during the period of its guidance or propulsion.
Ballistic conditions include the velocity, weight, shape, and size of the vehicle; likewise the density and temperature of the ambient element, the magnetic field, etc.
Thus, if the actual density distribution produced the same effect upon a projectile as the standard density distribution, the ballistic density would be 100 percent .
A ballistic missile is guided during a portion of its flight, usually the upward portion, and is under no thrust from its propelling system during the latter portion of its flight; it describes a trajectory similar to that of an artillery shell.
A rocket without lifting surfaces is in a ballistic trajectory after its engines cease operating.
2. = absorption band.
3. A group of tracks on a magnetic drum.
4. = auroral band. See aurora.
See aurora.
2. In a wave, the least frequency interval outside of which the power spectrum of a time-varying quantity is everywhere less than some specified fraction of its value at a reference frequency.
3. The number of cycles per second between the limits of a frequency band.
Sense 2 permits the spectrum to be less than the specified fraction within the interval. Unless otherwise stated, the reference frequency is that at which the spectrum has its maximum value.
4. In information theory, the information-carrying capacity of a communications channel.
Bang-bang in this term is imitative, arising from the noise made by control mechanisms slamming first to one side, then to the other, in this sort of control.
Some writers have used bar as equivalent to barye (1 dyne per square centimeter).
A unit of area for measuring a nuclear cross section. One barn equalssquare centimeter.
Barotropy is the state of zero baroclinity. Since the presence of solenoids (baroclinity) complicates the dynamics of the fluid, there has been much investigation of the extent to which an atmosphere, though obviously a baroclinic fluid, can be dynamically treated as barotropic. See equivalent-barotropic model.
2. An atmospheric wave of cyclonic scale in which troughs and ridges are approximately vertical.
is the relative vorticity and f is the coriolis parameter. This equation may also be interpreted as governing vertically averaged flow in which divergence is present but wind direction is constant with height. See equivalent barotropic model.
is the density; p is the pressure; and B is a function of thermodynamic variables, called the coefficient of barotropy. With the equation of state, this relation determines the spatial distribution of all state parameters once these are specified on any surface. For a homogeneous atmosphere, B=0; for an adiabatic atmosphere,
2. The geodesic line between two stations operating in conjunction for the determination of a line of position, as the two stations constituting a loran rate.
3. In radar, the line traced on amplitude-modulated indicators which corresponds to the power level of the weakest echo detected by the radar. It is retraced with every pulse transmitted by the radar, but appears as a nearly continuos display on the scope.
Target signals show up as perpendicular deviations from the base line; range is measured along the base line; signal strength is indicated by the magnitude of the deviations; and the type of target usually can be determined by the appearance of the deviations.
The control of the time sharing of a single transponder between several ground transmitters through the use of suitable coded timing signals.
Either of two scales sometimes used to graduate hydrometers; one scale is for liquids heavier than water, the other for liquids lighter than water.
Cygni (Deneb), 
Orionis (Rigel), and 
Ursae Majoris (Alkaid). See navigational
stars. 2. A structure, building, or station where such a device is mounted or located. See radar beacon, radio beacon.
Beacon skipping can be caused by interference, overinterrogation of beacon, antenna nulls, or pattern minimums.
2. A beam (sense 1) of radio waves used as a navigation aid.
3. = electron beam.
4. A body, one of whose dimensions is large compared with the others, whose function is to carry lateral loads (perpendicular to the long dimension) and bending movements.
The beam width of a radar determines the minimum angular separation which two targets can have and still be resolved. Roughly speaking, two targets at the same range whose angular separations at the radar antenna exceeds one-half of the beam width between half-power points will be resolved or distinguishable as two individual targets. The smaller the beam width, the greater the annular resolving power. Beam width may be at different locations through the axis depending upon the shape of the antenna reflector.
A bearing is often designated as true, magnetic, compass, grid, or relative as the reference direction is true, magnetic, compass, or grid north, or heading, respectively.
At one time bearing was restricted to reference to the direction of a terrestrial object or point as distinguished from azimuth which referred to the direction of a celestial body. This distinction has been blurred by usage.
Bearing angle is labeled with the reference direction as a prefix and the direction of measurement from the reference direction as a suffix. Thus, bearing angle N 37° W is 37° west of north, or bearing 323°.
This process may be controlled to produce a desired beat frequency. See heterodyne .
With
For values of z less than about 70°, the Bemporad formula can be replaced by the simpler approximate formula,
2. Popularly used as synonymous with aeroembolism (sense 2).
1. In aeronautics, a law or theorem stating that in a flow of incompressible fluid the sum of the static pressure and the dynamic pressure along a streamline is constant if gravity and frictional effects are disregarded.
From this law it follows that where there is a velocity increase in a fluid flow there must be a corresponding pressure decrease. Thus an airfoil, by increasing the velocity of the flow over its upper surface, derives lift from the decreased pressure.
2. As originally formulated, a statement of the conservation of energy (per unit mass) for a nonviscous fluid in steady motion. The specific energy is composed of the kinetic energy u2/2, where u is the speed of the fluid; the potential energy gz, where g is the acceleration of gravity and z is the height above an arbitrary reference level; and the work done by the pressure forces of a compressible fluid
v dp, where p is the pressure, v is the specific volume, and the integration is always with respect to values of p and v on the same parcel. Thus, the relationship 
= Constant along a streamline
is valid for a compressible fluid in steady motion, since the streamline is also the path. If the motion is also irrotational, the same constant holds for the entire fluid.
Increase of atomic number occurs with negative beta particle emission, decrease with positive beta particle (positron) emission or upon electron capture.
-factorIn plasma physics, the ratio of the plasma kinetic pressure to the magnetic pressure.
If
is less than 1, the magnetic field has a chance to contain the plasma providing there are no instabilities. If is larger than 1, there is no possible chance of containment.
-ray A stream of beta particles.
Betatron refers to the accelerated particles, electrons, which are identical with beta particles.
An example is an incorrectly set zero adjustment.
2. =binary cell.
3. =binary star.
Binary notation employs only two digits, 1 and 0, therefore is used extensively in computers where the on and off positions of a switch or storage device can represent the two digits. In decimal notation
The smaller star of the system is referred to as the companion or comes.
Visible binaries are those which can be resolved into two stars by a telescope.
Spectroscopic binaries are those which cannot be resolved by a telescope by show temporary displacement and doubling of the lines in their spectra.
2. The energy required to break chemical, atomic, or molecular bonds.
where the terms Ai (i = 1,2,3...) are given by the formula and where a can be positive, negative, fractional or whole. When the magnitude of z is less than 1, the higher powers get smaller and smaller and the formula can be made as precise as one wishes by including enough of them (for z of small magnitude, 1-2 terms are sufficient), although the result is never exact. For magnitudes of z equal to 1 or more, the formula only holds for values of a which are positive whole numbers. In that case, for any z, the result is exact and the sum of terms with powers of z does not go on arbitrarily but ends with z a.
For example, the decimal digit 7 is represented in biquinary notation by 12 [(1 x 5) + (2 x 1)], and the decimal quantity 3648 is represented by 03 11 04 13.
The abacus is based on biquinary notation.
For example, any reflector that scatters the incident energy.
2. A single character of a language employing only two distinct kinds of characters.
3. A quantity of intelligence which is carried by an identifiable entity and which can exist in either of two states.
4. A unit of storage capacity; the capacity in bits of a storage device is the logarithm to the base two of the number of possible states of the device.
5. A quantum of information.
6. Loosely, a mark.
2. Colloquially, any unit, usually an electronic device such as an amplifier, which can be mounted in, or removed from, a rocket, spacecraft, or the like as a single package.
1. An ideal emitter which radiates energy at the maximum possible rate per unit area at each wavelength for any given temperature. A blackbody also absorbs all the radiant energy in the near visible spectrum incident upon it.
No actual substance behaves as a true blackbody, although platinum black and other soots rather closely approximate this ideal. However, one does speak of a blackbody with respect to a particular wavelength interval. This concept is fundamental to all the radiation laws, and is to be compared with the similarly idealized concepts of the white body and the gray body. In accordance with the Kirchhoff law, a blackbody not only absorbs all wavelengths, but emits at all wavelengths and does so with maximum possible intensity for any given temperature.
2. A laboratory device which simulates the characteristics of a blackbody (sense 1). See hohlraum.
The spectral distribution of blackbody radiation is described by Planck law and the related radiation laws. If a very tiny opening is made into an otherwise completely enclosed space (hohlraum), the radiation passing out through this hole when the walls of the enclosure have come to thermal equilibrium at some temperature will closely approximate ideal blackbody radiation for that temperature.
Blackouts are most common in, but are not restricted to, the arctic. An arctic blackout may last for days or even weeks during periods of intense auroral activity. Past experiments with high-altitude nuclear detonations have produced blackouts and artificial auroras over the subtropics .
2. A fadeout of radio and telemetry transmission between ground stations and vehicles traveling at high speeds in the atmosphere caused by signal attenuation in passing through ionized boundary layer (plasma sheath) and shock wave regions generated by the vehicle.
3. A vacuum tube characteristic which results from the formation of a dielectric film on the surface of the control grid.
A negative charge, accumulated on the film when the grid is driven positive with respect to the cathode, affects the operating characteristics of the tube.
4. A condition in which vision is temporarily obscured by a blackness, accompanied by a dullness of certain of the other senses, brought on by decreased blood pressure in the eye and a consequent lack of oxygen, as may occur, e.g., in pulling out of a high-speed dive in an airplane. Compare grayout, redout.
2. A vane (in sense 2), such as a rotating vane or stationary vane in a rotary air compressor, or a vane of a turbine wheel.
2. The characteristic instantaneous rise in pressure, followed by a sudden decrease, that results from this movement, differentiated from less rapid pressure changes.
3. To take off from a launching pad or stand. Said of a rocket in reference to the blast effects caused by rapid combustion of fuel as the rocket starts to move upward. (Popular).
This term is commonly used for explosion, but the two terms should be distinguished. In space, an explosion could take place, but no blast would follow.
is the local change of wind direction, 
is the wind angle, and t is time. The curvatures and change of wind direction are positive for cyclonic flow.
The abnormal gradient of the index of refraction resulting from a blob can produce a radar echo of the type known as angels.
2. The activity that works in such a structure.
Blocking oscillators are used in digital computers.
The downstream side may or may not be reduced in pressure to provide greater expansion potential.
A parameter of a conic related to the eccentricity, e, of the conic in the following way:
For hyperbolas and prolate ellipses,
- For oblate ellipses,
2. In a general sense, any fabrication, structure, or other material form, especially one aerodynamically or ballistically designed, as, an airfoil is a body designed to produce an aerodynamic reaction.
2. A type of landing-gear unit consisting of two sets of wheels in tandem with a central strut.
A constant equivalent to the magnetic moment of an electron, erg/gauss. See physical constants, tables.
Bohr magneton is sometimes used as a synonym for
The smallest possible radius of an electron orbit in the Bohr model of the atom, centimeters.
The temperature at which the equilibrium vapor pressure between a liquid and its vapor is equal to the external pressure on the liquid. Compare ice point.
Two identical, blackened, thermally sensitive electrical resistors are used in a Wheatstone bridge circuit. Radiation is allowed to fall on one of the elements, causing a change in its resistance. The change is a measure of the intensity of the radiation.
The magnitude measured within the earth's atmosphere by a bolometer is the radiometric magnitude.
2. Loosely = radiometric magnitude.
The ratio of the universal gas constant to Avogadro's number; equal to called gas constant per molecule, Boltzmann universal conversion factor .
The Bond albedo is used in planetary astronomy.
2. Gluing or cementing together for structural strength.
Boolean algebra corresponds to an algebra using only the numbers 0 and 1, therefore can be used in programming digital computers which operate on the binary principle.
2. Boost pressure.
3. To supercharge.
4. To launch or to push along during a portion of flight, as to boost a ramjet to flight speed by means of a rocket, or a rocket boosted to altitude with another rocket .
2. = launch vehicle.
2. A rocket used to set a vehicle in motion before another engine takes over.
In sense 2 the term launch vehicle is preferred.
See constellation.
Such a system must be started in its operation by outside power or propellants. When its operation is no longer dependent on outside power or propellant the system is said to be in bootstrap operation.
2. In computer operations, the coded instructions at the beginning of an input tape which together with manually inserted instructions, initiate a routine.
3. = leap-frog. See, leapfrog test.
is the attenuation coefficient (or extinction coefficient) of the medium at wavelength 
; 
is the flux density at the source; and x is the distance from the source. Sometimes called Beer law, Lambert law of absorption . See absorption coefficient, scattering coefficient.
In aerodynamics the boundary-layer thickness is measured from the surface to an arbitrarily chosen point, e.g., where the velocity is 99 percent of the stream velocity. Thus, in aerodynamics, boundary layer by selection of the reference point, can include only the laminar boundary layer or the laminar boundary layer plus all, or a portion of, the turbulent boundary layer.
In theory, this maneuver will allow a spacecraft to dissipate the heat generated in entry without burning up.
2. The point in a computer program at which the machine will proceed with one of two or more possible routines according to existing conditions and instructions.
Bonding results from the intimate contact produced by the dissolution of a small amount of base metal in the molten filler metal, without fusion of the base metal. Sometimes, the filler metal is put in place as a thin solid sheet or as cladding and the composite is heated as in furnace brazing.
The term brazing is used where the temperature exceeds some arbitrary value, such as 800°F; the term soldering is used for temperatures lower than the arbitrary value.
2. To prepare a breadboard , sense 1.
Electromagnetic radiation produced by the rapid change in the velocity of an electron or another fast, charged particle as it approaches an atomic nucleus and is deflected by it. See bremsstrahlung effect.
In cosmic-ray shower production, bremsstrahlung effects give rise to emission of gamma rays as electrons encounter atmospheric nuclei. The emission of radiation in the bremsstrahlung effect is merely one instance of the general rule that electromagnetic radiation is emitted only when electric charges undergo acceleration.
The cessation of burning in a rocket, resulting from consumption of the propellants, from deliberate shutoff, or from other cause; the time at which this cessation occurs. See burnout, cutoff.
This neutral point, discovered by Brewster in 1840, is located about 15° to 20° directly below the sun; hence it is difficult to observe because of the glare of the sun.
2. = luminance.
In sense 2 luminance is preferred.
2. The temperature of a nonblackbody determined by measurement with an optical pyrometer.
A parameter describing the hardness of a material as the ratio of pressure on a standard sphere used to indent the material to be tested to the area of the indentation produced.
The amount of heat required to raise 1 pound of water at 60 degrees F, 1° F.
This unit is defined for various temperatures, but the general usage seems to be to take the Btu as equal to 252 15° gram-calories or 1055 joules.
2. The lateral deflection of a thin-walled body resulting from such instability.
2. A storage device used to compensate for a difference in rate of flow of information or time or occurrence of events when transmitting information from one device to another.
The opposite is fade.
Burble occurs over an airfoil operating at an angle of attack greater than the angle of maximum lift, resulting in a loss of lift and an increase of drag. See compressibility burble.
The velocity at which a solid propellant in a rocket is consumed.
Burning rate is measured in a direction normal to the propellant surface and is usually expressed in inches per second.
A constant, related to initial grain temperature, used in calculating the burning rate of a rocket propellant grain.
The exponent n in the equation
The value of n varies with the propellant.
In the United Kingdom all burnt is preferred to burnout.
2. An act or instance of something burning out or of overheating; specifically, an act or instance of a rocket combustion chamber, nozzle, or other part overheating so as to result in damage or destruction.
2. = solar radio burst.
3. = cosmic ray burst.
2. Sustained oscillation of an aerodynamic control surface caused by intermittent flow separation on the surface, or by a motion of shock waves across the surface, or by a combination of flow separation and shock-wave motion on the surface.