The sabot separates from the projectile after launching.
See constellation.
See constellation.
Samples may be taken at random or systematically. The sample is taken in an attempt to estimate the population.
At the end of each saros the sun, moon, and line of nodes return to approximately the same relative positions and another series of eclipses begins, closely resembling the series just completed.
2. A manmade object that revolves about a spatial body, such as Explorer I orbiting about the earth. See spacecraft, table XIV [not reproduced].
3. Such a body intended and designed for orbiting, as distinguished from a companion body that may incidentally also orbit, as in the observer actually saw the orbiting rocket rather than the satellite.
4. An object not yet placed in orbit, but designed or expected to be launched into an orbit.
The saturation vapor pressure of any pure substance, with respect to a specified parent phase, is an intrinsic property of that substance and is a function of temperature alone (see Clapeyron-Clausius equation).
2. = equilibrium vapor pressure.
Owing to the release of latent heat, this lapse rate is less than the dry-adiabatic lapse rate, and the differential equation representing the process must be integrated numerically. Wet-bulb potential temperature is constant with height in an atmosphere with this lapse rate.
A scalar quantity is distinguished from a vector quantity by the fact that a scalar quantity possesses only magnitude, whereas a vector quantity possesses both magnitude and direction.
between their positive directions. Also called dot product, direct product, inner product. See vector product. For two vectors A and B, the scalar product is most commonly written A
B,
read A dot B, and occasionally as (AB). If the vectors A and B have the components
Ax, Bx, and Ay, By, and Az,
Bz along rectangular Cartesian, x, y, and z axes, respectively,
then
If a scalar product is zero, one of the vectors is zero or else the two are perpendicular.
A measure of the relationship between density and temperature of any point in an atmosphere; the thickness of a homogeneous atmosphere which would give the observed temperature:
where k is the Boltzmann constant; T is the absolute temperature; m and M are the mean molecular mass and weight, respectively, of the layer; g is the acceleration of gravity; and R* is the universal gas constant. Compare virtual height.
The number of input pulses per output pulse of a scaler is termed the scaling factor. A binary scaler is a scaler whose scaling factor is 2. A decade scaler is a scaler whose scaling factor is 10.
Scanning usually follows a systematic pattern involving one or more of the following: (1) In horizontal scanning (or searchlighting), the antenna is continuously rotated in azimuth around the horizon or in a sector (sector scanning); used to generate plan-position-indicator-scope displays. (b) Vertical scanning is accomplished by holding the azimuth constant but varying the elevation angle of the antenna; used in height-finding radars to generate the relative-height-indicator-scope display. (c) For conical scanning, a somewhat offcenter radiating element is rotated while its parabolic reflectors fixed in position so that the radiated beam generates a concially shaped volume with the antenna at the apex; used to determine accurate bearing and elevation angle of targets and employed in automatic tracking radars. (d) In helical scanning (or spiral scanning) the azimuth and elevation angle of the antenna are constantly varied so that at a given distance from the radar the radiated beam generates the surface of a hemisphere; used for radio direction finding, in certain types of search radars, and in tracking radars to search areas for targets.
2. The relative dispersion of points on a graph, especially with respect to a mean value, or any curve used to represent the points. See dispersion.
3. To accomplish scattering.
Convention varies as to whether this angle is measured with respect to the direction in which the incident radiation was advancing or with respect to the direction from scatterer to radiation source.
Recognition of this process and the development of specialized equipment (basically, more powerful transmitters and sensitive receivers) has greatly increased the range of VHF and UHF communication. The over-all technique is known as scatter communication.
Along with absorption, scattering is a major cause of the attenuation of radiation by the atmosphere. Scattering varies as a function of the ratio of the particle diameter to the wavelength of the radiation. When this ratio is less than about one-tenth, Rayleigh scattering occurs in which the scattering coefficient varies inversely as the fourth power of the wavelength. At larger values of the ratio of particle diameter to wavelength, the scattering varies in a complex fashion described by the Mie theory; at a ratio of the order of 10, the laws of geometric optics begin to apply.
1. Regions of different density in a fluid, especially as shown by special apparatus.
2. Pertaining to a method or apparatus for visualizing or photographing regions of varying density in a field of flow. See schlieren photography, scintillation.
Used in compounds, such as schlieren lens, schlieren method, schlieren photograph, etc.
A simulated Schuler pendulum carried in a vehicle moving in the earth's gravitational field would always indicate the true vertical.
If the object lies outside the earth's atmosphere, as in the case of stars and planets, the phenomenon is termed astronomical scintillation; if the luminous source lies within the atmosphere, the phenomenon is termed terrestrial scintillation. As one of the three principal factors governing astronomical seeing, scintillation is defined as variations in luminance only. It is clearly established that almost all scintillation effects are caused by anomalous refraction occurring in rather small parcels or strata of air, schlieren, whose temperatures and hence densities differ slightly from those of their surroundings. Normal wind motions transporting such schlieren across the observer's line of sight produce the irregular fluctuations characteristic of scintillation. Scintillation effects are always much more pronounced near the horizon than near the zenith. Parcels of the order of only centimeters to decimeters are believed to produce most of the scintillatory irregularities in the atmosphere.
2. A flash of light produced in a phosphor by an ionizing event. See scintillation counter. 3. On a radar display, a rapid apparent displacement of the target from its mean position. Also called target glint or wander.
This includes but is not limited to shift of effective reflection point on the target.
Because of possible ambiguity this term should be avoided in formal reports.
See constellation.
Scotopic vision is associated with rod function.
2. A surface on which images are displayed, as the face of a cathode-ray tube.
See constellation.
See constellation.
See
The unit of time, the second, was defined originally as the fraction 1/86 400 of the mean solar day. The exact definition of the "mean solar day" was left to astronomers, but their measurements have shown that on account of irregularities in the rotation of the Earth, the mean solar day does not guarantee the desired accuracy. In order to define the unit of time more precisely, the 11th CGPM (1960) adopted a definition given by the International Astronomical Union which was based on the tropical year [see ephemeris second]. Experimental work had, however, already shown that an atomic standard of time-interval, based on a transition between two energy levels of an atom or a molecule, could be realized and reproduced much more accurately. Considering that a very precise definition of the unit of time of the International System, the second, is indispensable for the needs of advanced metrology, the 13th CGPM (1967) decided to replaced the defintion of the second by the following:
The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom (13th CGPM (1967), Resolution 1).
The previous is an excerpt (with the exception of the reference to "ephemeris second") from WWW version of the National Institute of Standards and Technology: Physics Laboratory's International System of Units (SI)
It follows from this law that during an adiabatic process, entropy cannot decrease. For reversible adiabatic processes entropy remains constant, and for irreversible adiabatic processes it increases. Another equivalent formulation of the law is that it is impossible to convert the heat of a system into work without the occurrence of other simultaneous changes in the system or its environment. This version, which requires an engine to have a cold source as well as a heat source, is particularly useful in engineering applications. See first law of thermodynamics.
2. A celestial body revolving around another body, its primary.
3. A particle emitted in secondary emission.
The yield or ratio of secondary to primary electrons is a function of the primary electron energy.
2. = cloud seeding.
Recent studies show that seeing is a combination of three principal and distinct effects that the human eye is not capable of distinguishing: (a) scintillation, i.e., fluctuations in brightness; (b) transverse displacements of the image; and (c) variations of the radius of curvature of the wavefront rendering the image in an out of focus.
A substance which absorbs in such fashion is called a selective absorber and is to be contrasted with an ideal blackbody, white body, or gray body. In reality, all substances are selective absorbers when due regard is paid to their interaction with all wavelengths of the complete electromagnetic spectrum.
In general, the largest and most complex degree of selectivity is found for wavelengths nearly equal to the diameter of the scattering particles.
2. Specifically, referring to positions on the moon measured in latitude from the moon's equator and in longitude from a reference meridian.
In active homing guidance the information received is in response to transmissions from the craft. In passive homing guidance natural radiations from the destination are utilized.
2. Half the angle at the observer subtended by the visible disk of a celestial body.
One-half the longest diameter of an ellipse.
One-half the shortest diameter of an ellipse.
For example, a perfect corner reflector is invisible to a circularly polarized radar because it reverses the sense.
Sensible temperature depends on the air temperature; radiation from the sun, sky, and surrounding objects; relative humidity; and air motion. The wet-bulb temperature is often taken as an approximate measure.
2. In measurements, the derivative representing the change in instrument indication produced by a change in the variable being measured.
2. The nerve endings or sense organs which receive information from the environment, from the organism, or from both.
2. The moment of this action.
See constellation.
2 Pertaining to or incorporating a servomechanism.
It should be noted that servomechanism and regulator are not mutually exclusive terms; their application to a particular system will depend on the method of operation of that system.
2. To place a binary cell in the one state.
See constellation.
As originally used, the term applied only to instruments having an arc of 60 degrees, a sixth of a circle, from which the instrument derived its name. Such an instrument had a range of 120 degrees. In modern practice the term applies to a similar instrument, regardless of its range, very few modern instruments being sextants in the original sense.
2. = atmospherics.
Such observations are more commonly obtained from networks of two or three widely spaced stations. Simultaneous observations of the azimuth of the discharge are made at all stations and the location of the storm is determined by triangulation.
By extension, the term is applied to a similar condition when any form of radiant energy is cut off by an obstruction, as a radar shadow. The darkest part of a shadow in which light is completely cut off is called the umbra; a lighter part surrounding the umbra, in which the light is only partly cut off, is called the penumbra.
Useful in space, a shadow shield is less effective in the earth's atmosphere because air scattering deflects radiation around it.
2. The optical method or technique by which this is done. A shadowgraph differs from a schlieren photograph in that the schlieren method depends on the first derivative of the refractive index while the shadow method depends on the second derivative. Interference measurements give the refractive index directly.
A shear plane wave in an isotropic medium is called a transverse wave.
A shield may be designated according to what it is intended to absorb, as a gamma-ray shield or neutron shield, or according to the kind of protection it is intended to give, as a background, biological, or thermal shield. The shield of a nuclear reactor is a body of material designed to prevent the escape of neutrons and radiation into a protected area, which frequently is the entire space external to the reactor. It may be required for the safety of personnel or to reduce radiation sufficiently to allow use of counting instruments.
2. A blow, impact, collision, or violent jar.
3. A sudden agitation of the mental or emotional state or an event causing it.
4. The sudden stimulation caused by an electrical discharge on the animal or human organism (e.g., electric shock).
2. The front side of a shock wave.
A short range trajectory measuring system using the intersections of the ellipsoids of Dovap and the hyperboloids of Dovap elsse or telemetry elsse during a rocket launch.
2. The flight of a rocket, as, the rocket made a 200-mile shot.
2. The wave components lying within such a band.
Although sidereal generally refers to the stars and tropical to the vernal equinox, sidereal time and the sidereal day are based upon the position of the vernal equinox relative to the meridian. The sidereal year is based upon the stars.
Because of the precession of the equinoxes, the sidereal day thus defined is slightly less than the period of rotation with respect to the stars, but the difference is less than 0.01 second. The length of the mean sidereal day is 24 hours of sidereal time or 23 hours 56 minutes 4.09054 seconds of mean solar time.
2. Specifically, the interval between two successive returns of an earth satellite in orbit to the same geocentric right ascension.
Sidereal time may be designated as local or Greenwich as the local or Greenwich meridian is used as the reference. When adjusted for nutation, to eliminate slight irregularities in the rate, it is called mean sidereal time.
Because of the precession of the equinoxes this is about 20 minutes longer than a tropical year.
2. The information to be conveyed over a communication system.
3. Any carrier of information; opposed to noise.
The signal level at some specified position near the source may be taken as the zero reference level. In an acoustic system the signal level is often in the form of a sound pressure level; either the reference sound pressure or the reference sound pressure level must be specified.
The higher the S/N ratio, the less the interference with reception.
It is constructed in the following manner. A silver disk located at the lower end of a diaphragmed tube serves as the radiation receiver for a calorimeter. Radiation falling on the silver disk is periodically intercepted by means of a shutter located in the tube, causing temperature fluctuations of the calorimeter which are proportional to the intensity of the radiation. The instrument is normally used as a secondary instrument and is calibrated against the water-flow pyrheliometer. It is used by the U.S. Weather Bureau as a standard instrument.
x + 
)
where y is the simple harmonic quantity; A is the amplitude;
is the angular frequency; x is the
independent variable; and
is the phase of the oscillation. The maximum value of the simple harmonic quantity is the amplitude A; it is sometimes called, for emphasis, the single amplitude to distinguish it from double amplitude which for a simple harmonic quantity is the same as the total excursion or peak-to-peak value. When a simple harmonic quantity is expressed as a complex quantity, the term amplitude must be used with caution in view of possible confusion with the alternate meaning of amplitude as the angle or argument of a complex quantity.
2. A heat sink. See source.
Sinking occurs whenever the rate of density decreases with height through the atmosphere is of smaller magnitude than normal or, in extreme cases, where the density actually increases with height.