[437] abiotic - not involving or not produced by living organisms

absorption spectrum - array of lines and bands that results from the passage of radiant energy from a continuous source through a cooler, selectively absorbing medium

activation energy - amount of energy needed to initiate a reaction

adsorption - adhesion to a surface in an extremely thin (often monomolecular) layer

albedo - fraction of incident electromagnetic radiation reflected by a body such as a planet, star, or cloud

allotropy - existence of an element in more than one form

amino acid - acid containing the amino (NH₂) group; more than 80 amino acids are known, but only about 20 occur naturally in living organisms, serving as the building blocks of proteins

anaerobic - occurring in the absence of free oxygen

Angstrom (Å) - unit of length convenient for measuring wavelengths of electromagnetic radiation: 1 Å=10^-10 m

aperture - in the case of a telescope, an area open to the Universe; signifies either the maximum physical or the effective capture cross section of a telescope or radio antenna; often stated in terms of the diameter or an equivalent diameter if the aperture is noncircular

apoprotein - protein portion of a conjugated protein (i.e., a compound of a protein with a nonprotein)

arcsecond (arcsec) - measurement of angular separation: a 1-inch stick would subtend an angle of 1 arcsec at a viewer's eye at a distance of about 6.5 miles

Arecibo - short name for the National Astronomy and ionospheric Center (NAIC) at Arecibo, Puerto Rico; often refers only to the NAIC 1OOO-ft (305-m) zenith (±20°) antenna, the world's largest radio astronomy collector

[438] artefact - material object modified purposefully for use by the person or animal that does the modifying

astrometry - branch of astronomy that focuses on measurements, especially those relating to positions and movements

astronomical unit (AU) - mean Earth-Sun distance: 1 AU = 1.496 x 10¹¹ m = 8.31 light minutes; a convenient unit for measuring distances between planets and their stars

atmosphere - gaseous mass enveloping a planet or star

atom epoch - fourth epoch in the history of the Universe, lasting from about 100 sec to 10⁶ yr, in which matter came to dominate radiation as the principal constituent of the Universe

atomic mass unit - convenient unit for measuring the mass of an atom or molecule: 1 atomic mass unit is defined as 1/12 the atomic mass of the most abundant carbon isotope, ¹²C

AU - see astronomical unit

autotroph - organism whose metabolism requires only external sources of carbon dioxide and nitrogen

bacterium - any of an extremely flexible class of microscopic plants whose members have a variety of structures, come singly or in colonies, live just about anywhere, and derive energy from whatever source is available

Big Bang - hypothesized initial singularity that could have started the space and time of our Universe, now thought to have occurred 7 to 20 billion years ago

billion - one-thousand million, 10⁹

bin - output signal channel in a multichannel spectrum analyzer or MCSA (q.v.)

binary system - two neighboring stars that revolve around their common center of gravity; the fainter of the two stars is called the companion

binwidth - nominal frequency bandwidth of a bin; see resolution binwidth

biosphere - general term for regions in which life can exist

blackbody - body capable of absorbing energy of all wavelengths falling on it; it is also capable of radiating all frequencies in a particular ratio to its absorbing properties. The value of the ratio depends only on the temperature of the body. The physical laws describing the properties of a blackbody are derived from the theory of thermodynamic equilibrium

black hole - gravitationally collapsed mass from which nothing - light, matter, or any other kind of signal - can escape; a theoretical concept so far

blue-green algae - any of a class of algae (a group of mainly aquatic, simple photosynthetic plants) whose chlorophyll is marked by bluish-green pigments

body plan - basic architectural arrangement of a biological structure

[439] carbohydrate - organic compound consisting of a chain of carbon atoms to which hydrogen and oxygen, present in a 2:1 ratio, are attached

carrier signal - electromagnetic wave whose modulations are used as signals in television and other radio transmissions

cassegrain (telescope or focus) - some telescopes, particularly at microwave and shorter wavelengths, have a second reflector near the focus of the larger, primary mirror. This translates the focal point to a position near the apex of the primary where it is more accessible, and where practice antenna feeds are less responsive to radiations arriving from very wide angles relative to the nominal pointing direction

cation hydration - process of incorporating molecular water into a complex molecule with positively charged units of another species

celestial sphere - the visible, seemingly spherical surface that appears to surround Earth and to be centered at the observer

CETI - acronym for communication with extraterrestrial intelligence. Sometimes pronounced with a long e and short i, to distinguish it from SETI which is favored with two short vowels

chaos - hypothetical first epoch in the history of the Universe, lasting 10^-23 sec - a period about which we cannot yet even speculate

chemically peculiar stars - stars manifesting anomalies in the relative abundances of elements, which may arise from mechanical rather the nuclear effects; so-called manganese stars, for example, show a area overabundance of manganese and gallium, usually accompanied by excess mercury

chemisorption - use of chemical forces to take up and hold onto something

chemoautotrophic - autotrophic and deriving energy from an inorganic compound (such as sulfur)

chemosynthesis - synthesis of organic compounds using energy derived from chemical reactions

chert - hard, flinty, siliceous rock, often arising through precipitation

chondrite - stony meteorite with small, rounded occlusions, usually of olivine or pyroxene, embedded in a matrix

chromosome - a gene-containing filamentous body found in cell nuclei

clade - group of organisms all descended from a single common ancestor

clay - earthy material, composed mainly of hydrous aluminum silicates and other minerals, which is plastic when moist but hard when fired

climate - long-term manifestations of short-term atmospheric variations

cluster (astronomical) - group of stars numbering from a few to hundreds of thousands of stars. Galactic clusters, sometimes called open clusters, contain up to a few hundred members and occur rather close to the plane of the Galaxy. Globular clusters contain tens of thousands of stars distributed about their center in a spherical manner and are found [440] far from the plane of the Galaxy as well as in it toward the center of the Galaxy

collagen - insoluble fibrous protein used by vertebrates to hold themselves together (i.e., it is a chief constituent of connective tissue fibrils and occurs in bones)

complex output - multichannel spectrum analyzer (MCSA, q.v.) may be set to give complex, undetected signal amplitude streams from each output channel in the form of two orthogonal quantities (a + jb). The more common format is to present detected signals by their amplitude or power (a² + b²), either with or without the associated angle = arctan b/a (via detection)

continuously habitable zone (CHZ) - region around a star in which a planet can maintain appropriate conditions for the existence of life (including the retention of a significant amount of liquid water) for a period sufficient to allow the emergence of life

core - central part of Earth, having a radius of about 2100 miles

cosmic rays - general term for the stream of atomic nuclei that constantly bombard Earth's atmosphere

crust - outer part of Earth, composed essentially of crystalline rocks

cryogenic - of or relating to the production of very low temperatures (on the Kelvin or absolute scale)

CW - continuous wave; a relative term of ancient lineage used to distinguish a simple wave with little or no modulation (e.g., a pure carrier (q.v.) or one simply keyed "on" and "off" as in manual radio telegraphy), vis-a-vis a highly complex, modulated wave (e.g., FM broadcasting)

dB - decibel; a unit of power ratio equal to 10 times the common logarithm of the ratio

decay constant - for an atom that undergoes radioactive decay, the decay constant is the proportionality factor between the time rate of decay and the total number of atoms present; it is the inverse of the mean lifetime of an atom

degassing - process whereby the atmosphere and ocean water have slowly accumulated through geologic time by emanating from Earth's interior in the form of volcanic gases

detection - in electromagnetics, an operation converting the vector electro-magnetic wave to a scalar time series proportional to either the amplitude or the power of the wave, with or without an accompanying angular time series. A crucial aspect of detection is: the signal-to-noise ratio after detection is the square of the signal-to-noise ratio before detection (vide complex output)

differential thermal analysis - method of determining, for samples being heated at a controlled rate, the intensities of and the temperatures at which thermal effects occur

[441] DNA - deoxyribonucleic acid; the molecule that is the basis of heredity in many organisms

Doppler shift - a change in frequency resulting from relative motion along the line between the transmitter and the receiver. If the source and the receiver are approaching each other, the frequency received is higher than the frequency transmitted by a factor, depending on the actual relative velocity. Knowledge of this shift is used to determine the relative velocity

drifting (signal) - refers to a signal with an apparent time rate of change in its typical frequency. All signals drift to some extent. In a SETI system, the dominant drift should be largely the result of only the time rate of change in the Doppler shift (q.v.)

ecology - study of the relationship between organisms and their environment

EIRP - equivalent isotropic radiated power; theoretical construct (all electromagnetic wave emitters are appreciably directive); product of real transmitted power and directive gain of the emitter (antenna) in the direction of the receiver (compared to the unit gain of the imaginary isotropic radiator)

electromagnetic radiation (wave, spectrum) - energy involving electric fields and magnetic fields oscillating in phase at right angles to each other, propagated in a direction at right angles to both fields with a velocity in free space equal to c (approximately 300,000 km/sec, or 186,000 miles/sec), a universal constant

encephalization - process of phylogenetic concentration and increase in nervous tissue

entropy - tendency of systems to become more disordered (and thus more uniform) over time; also a measure of disorder

epitaxial - growing on a crystalline substrate in such a way as to mimic the orientation of the substrate

eras (geologic) - all of Earth's history since the appearance of the first life forms is divided roughly into four eras: Precambrian, from 3.5 billion to 570 million years ago; Paleozoic, from 570 to 225 million; Mesozoic, from 225 to 65 million; and Cenozoic, from 65 million to the present. The last two eras are broken down into the following periods: the Mesozoic into Triassic, Jurassic, and Cretaceous; the Cenozoic into Tertiary and Quaternary

erg - the unit for work in the cgs system of units: the work done by a force of 1 dyne moving through a distance of 1 cm

ETI - extraterrestrial intelligence; also used to signify extraterrestrial intelligent species

eucaryote - organism composed of one or more cells with clearly formed nuclei

eutectic - form of a compound that has the lowest possible melting point

[442] evolution - change over time in the morphology and physiology of species of organisms; or of any object, such as stars; or of ideas; etc.

exobiology - extraterrestrial biology, that is, the study of life forms as they might occur outside the terrestrial environment

feed (antenna feed, line feed) - in a reflecting antenna system, the device that converts a guided (by wire, cable, or other wave guide) electromagnetic wave into an electromagnetic radiation field, and vice versa, when reciprocity theorem holds as it so often does. Commonly, feeds are some form of horn antenna, but they may be dipole arrays or their equivalent or linear devices like the Yagi antenna or the leaky multicavity line feed used with some spherical reflectors, as at Arecibo

Fischer-Tropsch-type (FTT) reaction - catalytic reaction in which hydrocarbons and their oxygen derivatives are produced through the reaction of hydrogen and carbon monoxide

flare (astronomical) - relatively rapid outburst of energy in a star

fossil record - remnants or traces of organisms of past geological ages embedded in Earth's crust

free radical - atom or group of atoms having at least one unpaired electron

freezing point shift - change in the freezing point of a solution compared to that of the pure solvent

fungus - plant of the Thallophyta subkingdom, which lacks chlorophyll and ranges in form from a single cell to massed bodies, including yeasts, molds, and mushrooms

Gaia hypothesis - hypothesis that the biosphere has an important modulatory effect on the surrounding atmosphere

gain stability - crudely defined by = g(t); the smaller this quantity over the relevant time interval, the less the gain instability or the greater the gain stability. Gain (amplification) of analog signaling systems always varies somewhat with time; g(t) contains a variety of "noise" terms of zero mean and various secular terms; the latter dominate unless proper precautions are in force

galaxy - spelled with a lower-case g, galaxy means any of millions of stellar systems once called "island universes" or extragalactic nebulae. Depending on their form, galaxies may be called spirals, barred spirals, ellipticals, or irregulars. Spelled with a capital G, Galaxy refers to that particular stellar system which includes our Sun and all the stars visible to the naked eye. The Milky Way is our view of the Galaxy

galaxy epoch - fifth epoch in the history of the Universe, lasting on the order of 10¹⁰ yr, during which matter largely coagulated into galactic masses

gamma ray - high-energy electromagnetic particle or photon, especially as emitted by a nucleus in its transition from one energy level to another

[443] gene pool - total amount of information in all the genes of all the reproductive members of a biological population at any given time

genetic drift - random fluctuations (or "walk") of gene frequencies from generation to generation that occur in small populations

genus - taxonomic category ranking below a family and above a species

giga - 10⁹ (as in gigahertz, GHz); one billion (U.S.A.)

glycoprotein - conjugated protein in which the nonprotein group is a carbohydrate

gravitational wave - propagating field predicted by general relativity to occur as a result of any large-scale change in the distribution of matter (as in the collapse of a star)

greenhouse effect - general warming of the lower layers of a planetary atmosphere that tends to increase with increasing atmospheric carbon dioxide. As with Earth, this process occurs whenever an atmosphere is relatively transparent to visible-light radiation but opaque to the longer wavelength infrared radiation of the surface of Earth

hadron epoch - second epoch in the history of the Universe, lasting on the order of a second; named for the heavy elementary particles (protons, neutrons, mesons) that were the most abundant form of matter at the time

halloysite - porcelainlike clay with a composition similar to that of kaolin but with more water and a distinct structure helium - atom consisting of two protons and two electrons

hertz (Hz) - measure of frequency; an oscillating system that completes a cycle a second has a frequency of 1 Hz

Hubble constant - constant of proportionality in the relation between distance of galaxies and their velocity of recession

hydrocarbon - organic compound containing only carbon and hydrogen

hydrogen - simplest atom, consisting only of one proton and one electron; the most abundant element in the Universe

hydrogenation - process of combining something (especially an unsaturated compound) with hydrogen

hydrosphere - aqueous envelope of Earth, including bodies of water and water vapor in the atmosphere hydrothermal vent - opening in the sea floor produced by the hot magmatic emanations that are rich in water Hz - see hertz

index of refraction - ratio of the speed of light in a vacuum to its speed in a given medium

infrared radiation - electromagnetic radiation with wavelengths longer than that of visible light and shorter than millimeter radio waves

interstellar clouds - masses of tenuous gas and dust between the stars

[444] ionosphere - that region of Earth's upper atmosphere having an appreciable abundance of electrons and charged atoms (ions), ranging from 50 to 500 miles above the ground

isotope - one of two or more atoms whose nuclei have the same number of protons but different numbers of neutrons

jansky (jy) - convenient unit of incident spectral flux density used in radio astronomy; 1 jy = 10^-26 W/m2 Hz (named for Karl G. Jansky, initial discoverer of extraterrestrial radio radiations)

joule (J) - unit for work in the mks system of units: 1 J = 10⁷ ergs

kaolinite - mineral (a hydrous silicate of aluminum) that constitutes a principal part of the fine clay, kaolin

Kardashev cultures - N. X. Kardashev has distinguished three types of technological societies according to the amount of power they can harness: Type I can engage the power available on a planet; Type II, the power output of a star; and Type III, the power output of a galaxy

kHz - kilohertz (see Hertz)

lepton epoch - third epoch in the history of the Universe, lasting about 100 see, in which the lighter elementary particles such as electrons, neutrinos, and muons were the dominant form of matter

Life Era - era in the history of the Universe when life emerges as the dominant element

light year - distance traveled by light in a vacuum in one year: 1 light year= 9.46 x 10¹⁵ m

lignification - deposition of lignin, the chief noncarbobydrate constituent of wood, in cell walls

lithosphere - outer (rocky) layer of the solid Earth, usually taken to be about 50 miles in depth

luminosity - relative brightness

luminosity class - two stars may be classified as of the same spectral type yet differ, perhaps widely, in intrinsic brightness or luminosity (see spectral type)

- (see solar mass)

magma - molten matter under Earth's crust, from which igneous rock is formed

magnetosphere - region of the upper atmosphere, extending out thousands of miles, dominated by Earth's magnetic field, so that charged particles are trapped in it

magnitude (stellar) - relative measure of the brightness of celestial objects. A difference of 1 magnitude in brightness corresponds to a luminosity difference of 10^0.4 2.51; a difference of 5 magnitudes corresponds to a factor of 10^{5 (0.4)} = 100 in luminosity

Main Sequence - principal sequence of stars on the graph of luminosity versus effective temperature, encompassing more than 90% of observable [445] stars. The lower mass limit for the Main Sequence is 0.085 and the upper limit is about 60

mantle - layer of Earth that lies below the lithosphere and above the core

Matter Era - collective name for the most recent three epochs in the history of the Universe (atom, galaxy, stellar), covering all of time after the Radiation Era

Maunder minimum - virtual disappearance of sunspots in the period 1645 to 1715

MCSA - short for MCSA/SD, a digital, energy-efficient, real-time, multi-channel spectrum analyzer and signal detector; hardware device that continuously accepts a significant portion of the electromagnetic spectrum and divides the spectral energy into a set of many contiguous frequency bins or output channels. Operational functions included are frequency analysis and signal detection, averaging, threshold testing, etc.

mega - 10⁶ (as in megahertz, MHz); one million

metamorphic rocks - rocks formed by the action of great heat and/or pressure

metazoan - an animal whose body is composed of cells differentiated into tissues and organs and (usually) a digestive cavity

MHz - one million Hertz; megahertz (see hertz)

micron - 10^-6 m

microwave - electromagnetic wave roughly in the range 0.01-1 m in wavelength (ordinary broadcasting utilizes waves in the 200-600 m range; the "short waves" used in long-distance communications are rarely shorter than 10 m)

midocean ridge - a 40,000-mile-long continuous median mountain range in the Arctic, North and South Atlantic, and Indian Oceans. The crest of the ridge is usually found at 500 to 1300 fathoms below the surface; its width is usually a few hundred miles, and it has a relief of 10,000-33,000 ft

mitochondrion - cytoplasmic organelle serving as a site of respiration

monomer - simple chemical compound of relatively low molecular weight which can undergo polymerization

montmorillonite - soft claylike mineral composed of hydrous aluminum silicate

multicellular - consisting of many cells

nebula - rarefied cloud of gas or dust observed in interstellar space

neoteny - attainment of sexual maturity during the larval stage

neutral point (in binaries) - point (barycenter) between a binary pair at which the gravitational attractions of the two stars cancel one another

neutron star - collapsed star whose core is composed primarily of neutrons at a density above 10¹⁴ gm/cm³

[446] noble gas - one of a group of rare but extremely stable gases with low reaction rates (helium, neon, argon, krypton, xenon, radon)

nucleic acids - long, chainlike molecules which, in the various combinations of constituent groups, embody the genetic code (DNA) and assist with its transmission (RNA)

nucleoside - compound consisting of a sugar and a purine of pyrimidine base

nucleosynthesis - production of the chemical elements from hydrogen nuclei or protons (such as occurs in thermonuclear reactions in stars)

nucleotide - compound composed of a nucleoside combined with phosphoric acid

oceanic basalts - rocks of the oceanic island volcanoes

organelle - specialized cellular part analogous to an organ

ozone layer - layer of Earth's atmosphere at about 20 to 30 miles, marked by a high ozone (0₃) content

paedomorphic transformation - phylogenetic change that involves retention of juvenile characteristics by the adult

panspermia - diffusion of spores or molecular precursors of life through space

parent compound - chemical compound that is the basis for one or more derivatives

parsec (pc) - parallax second, the distance at which 1 AU subtends an angle of 1 second of arc: 1 parsec = 3.086 x 10¹⁶ m = 3.26 light years

phase change - metamorphosis of a substance from one state to another, as from gas to liquid or from solid to gas

phase delay - signal travel time between two points in any signal path or circuit (measured in seconds or in degrees or radians of the signal frequency); to be distinguished from simultaneous phase difference between two points

photoautotrophic - autotrophic and deriving energy from light

photolysis - component process in photosynthesis in which water is dissociated and hydrogen is joined to a molecule of a substance called NADP under the indirect influence of solar energy

photon - quantum of electromagnetic energy, of value hV, where h is the Planck constant and v is the frequency of the radiation

photosynthesis - process by which light energy and chlorophyll manufacture carbohydrates out of carbon dioxide and water

phylum - category of taxonomic classification just above class

plastic - any of various cytoplasmic organelles of photosynthetic cells that serve in many cases as centers for metabolic activity

plate tectonics - model of the structure of Earth in which the surface consists of a small number of semirigid plates floating on a viscous underlayer [447] in the mantle; the clashing of plates concentrates most deformation, volcanism, and seismic activity along their peripheries

polarization - electromagnetic radiation that exhibits different properties in different directions at right angles to the line of energy propagation is said to be polarized

polymerization - process of forming long molecules (polymers) out of small units (monomers)

polynucleotide - polymeric chain of nucleotides

polypeptide - molecular chain of amino acids

prebiotic - relating to the chemical or environmental precursors of the origin of life

procaryote - cellular organism that does not have a distinct nucleus

Project Cyclops - a 10-week design study sponsored by NASA, Stanford University, and the American Institute for Engineering Education, of possible means for detecting extraterrestrial civilizations

prosthetic group - nonprotein group of a conjugated protein (i.e., a compound of a protein with a nonprotein)

protein - complex polymer built of amino acids that contains the elements carbon, hydrogen, nitrogen, oxygen, sometimes sulfur, and occasionally others such as phosphorus and iron. Proteins are essential constituents of all living cells; they are synthesized from raw materials by plants but assimilated as separate amino acids by animals

proteinoid coagulations - proteinlike linkages of amino acids produced under laboratory conditions from repeated heating and cooling of simple organic molecules

protist - any of a kingdom of living organisms (Protista) that includes algae slime molds, protozoa, and fungi, usually characterized by unicellular reproductive structures, true nuclei, and chromosomes

proton-proton cycle - energy-releasing nuclear reaction chain believed to be important in energy production in hydrogen-rich stars

pulsar - rotating, magnetized neutron star, emitting very energetic radio pulses at a rapid and very regular rate

purine - nitrogen base that forms a component (with sugar and phosphate of nucleotides and nucleic acids

pyrimidine - nitrogen base such as cytosine, thymine, or uracil that is a constituent of nucleotides and nucleic acids

quantum - a discrete small unit; in any given physical process, it is the minimum permissible unit of energy

quark - a possibly hypothetical particle that carries a fractional electric charge and is held to be a constituent of known elementary particles

quasar (quasi-stellar radio source) - object nearly stellar in appearance that emits visible light at a rate exceeding that of a large normal galaxy by a [448] factor of about 100 and that emits radio waves at a rate comparable to the strongest radio galaxies

Radiation Era - collective name for the first three epochs of the history of the Universe (chaos, hadron epoch, lepton epoch), lasting overall about 100 sec and dominated by radiation rather than matter

radioactivity - spontaneous emission from the nuclei of atoms of certain elements, of charged particles, and/or strong radiation; the remaining nucleus is generally an isotope of another element

radionuclide - radioactive nuclear species or nuclide

rare earth elements - series of elements usually taken to include elements with atomic numbers 58 to 71, lanthanum, and sometimes yttrium and scandium

red giant - luminous red star that has exhausted the supply of hydrogen in its core and evolved off the Main Sequence; as the core contracts and becomes hotter, helium burning starts and an extensive envelope develops as the outer regions of the star expand

redox potential - voltage difference at an inert electrode immersed in a reversible oxidation-reduction system

reducing atmosphere - atmosphere comprised of substances that readily provide electrons

refraction - bending of a wave front when the wave encounters a medium with propagation properties different from the one in which it has been traveling

resolution binwidth - equivalent power bandwidth, ; if p_m is the maximum of the real bin frequency response,p(v), then.

rift zone - elongated valley formed by the depression of a block of Earth's crust between two faults or groups of faults of approximately parallel strike

RNA (t, m) - ribonucleic acid; a nucleic acid generally associated with the control of chemical reactions. Transfer RNAs move particular amino acids to growing polypeptide chains in protein synthesis; messenger RNAs act as templates for the formation of proteins

roentgen - unit of X or gamma radiation dosage: The amount of such radiation sufficient to produce ions carrying 1 electrostatic unit of charge in 1 cm³ of air

seeing - in astronomy, this is the quality, not the act of observation; it refers to the atmospheric turbulence degrading an image and is measured by the smallest detail of the image that can be readily distinguished

sessile - attached directly by the base (rather than being raised on a stalk)

SETI - acronym for search for extraterrestrial intelligence, primarily by means of microwave radio exploration (pronounced with short e and i)

[449] shock wave - discontinuity in the flow of a fluid (including a gas or plasma) marked by an abrupt increase in pressure, temperature, and flow velocity at the shock front

sidereal time - time measured in relation to the fixed stars: the length of a sidereal day is 23 hr, 56 min, 4.09 sec of mean solar time

siderophile element - element with a weak affinity for oxygen and sulfur and readily soluble in molten iron (including iron, nickel, cobalt, platinum, gold, tin, and tantalum)

signal-to-noise ratio - ratio of the signal power in a signal channel to the (unwanted) noise power present smectite - class of clay minerals characterized by distinct swelling properties and high cation-exchange capacities (including montmorillonite, nontronite, etc.)

solar constant - rate at which radiant solar energy is received normally per unit area at the outer layer of Earth's atmosphere; its value is about 1.94 gram calories/cm²/min

solar mass () - mass of the Sun, 2 x 10³⁰ kg, used commonly as a unit to measure the masses of stars

solar nebula - cloud of gas and dust out of which a star condenses

solar (stellar) wind - radial outflow of hot plasma from a star's corona, carrying both mass, angular momentum, and energy away from the star

speckle interferometry - method of using short-exposure photographs to recover information down to the diffraction limit of large optical telescopes

spectral analysis - study of the distribution by wavelength or frequency of the radiation emitted by an object of interest

spectral type (or class) - classification used to sort stars by photospheric temperature and intrinsic brightness. The seven spectral classes O-B-A F-G-K-M, listed in order of decreasing temperature, include 99% of all known stars. Each spectral type is divided into a variable number of subtypes designated by Arabic numerals. Further, stars are sorted by intrinsic brightness into luminosity classes designated by the first five Roman numerals. In turn, these are subdivided into a small number of subclasses designated by the first few letters of the lower case English alphabet; for example, the Sun is a G2 V star (also sometimes denoted as a dwarf G2 star) and Betelgeuse ( Orionis) is classified as M2 lab (i.e., intermediate between la and lb)

spectroscopic binary - binary star that can be distinguished from a single star only through analysis of the Doppler shift of the spectral lines of one or both stars as they revolve about their common center of mass

spectroscopy - splitting of light into its constituent wavelengths.

[450] stellar epoch - sixth epoch in the history of the Universe, lasting perhaps 10¹⁰ yr from the galactic era to the present, dominated by the formation of stars

stromatolite - laminated sedimentary fossil formed from layers of blue-green algae

⁸⁷Sr/⁸⁶Sr ratio - strontium isotope ratio is used as a corrective factor in rubidium-strontium dating for studying the ultimate age of origin of igneous rock

sublimation - process of passing from gas to solid state (or vice versa) without becoming a liquid

supernova - phenomenon in which a star, at the end of its nuclear burning life, increases its energy output several billionfold for a short time. Some supernovae become as bright as the whole galaxy in which they are observed. A large fraction of the star is exploded into interstellar space, leaving behind a core which may become a white dwarf, a neutron star, or a black hole

superphylum - taxonomic category lying between a kingdom and a phylum

symbiosis - intimate living together of two organisms (called symbionts) of different species, for mutual or one-sided benefit

synchrotron emission - radiation from electrons constantly accelerated in a magnetic field at a rate great enough for relativistic effects to be important. Predicted long ago, this radiation was first encountered in the particle accelerator called the synchrotron. Much of the radiation observed by radio astronomers originates in this fashion

synchrotron self-absorption - reabsorption of radiation from accelerated electrons by other nearby electrons; this is a possible source of low-frequency turnovers observed in the radio spectra of compact sources

systems analysis - analysis of the response to inputs of a set of interconnected units whose individual characteristics are known

taxon (pi. taxa) - group of organisms constituting one of the formal units in taxonomic classification (phylum, order, etc.) and characterized by common characteristics in varying degrees of distinction

tessera - unit of a mosaic

tool - material object used to make other objects or to facilitate activities such as resource extraction

transfer function - mathematical relationship between the output of a system and its input

trophic level - level within a food chain in which all members are equally far removed from the primary food producers

T-tauri stars - luminous variable stars associated with interstellar clouds and found in very young clusters; they are believed to be still in the process of gravitational contraction from their protostellar phase and have not yet arrived at the Main Sequence and begun to burn hydrogen

[451] ultraviolet light - band of electromagnetic radiation from about 40 to 4000 Å.

Universe - everything that came into existence at the moment of the Big Bang, and everything that evolved from that initial mass of energy; or everything we can, in principle, observe

valence state - state of electrical imbalance in an atom or molecule

visual binary - binary star system whose components can be identified with an optical telescope

volatile organic compounds - class of organics that is easily vaporizable at low temperatures and pressures

WARC - World Administrative Radio Conference, usually convened every 20 years (1959, 1979, etc.); sponsored by the International Telecommunications Union (ITU), an organ of the United Nations (UN). These conferences draft treaties allocating radio spectrum space to the various services, such as broadcasting, radar, etc. Individual nations make transmitter assignments within their own territories. Treaty enforcement relies entirely on the individual and mutual advantages of international cooperation. There is only one radio spectrum

wave guide - special transmission medium resembling a pipe and often having a rectangular cross section, inside of which radio waves may be propagated

whistler - electromagnetic ultralow frequency radiation observed in planetary magnetospheres; energized by lightning and other discharges

Wm^-2 (or W/m² ) - watts per square meter of incident signal flux per whatever resolution bandwidth is in use. It is the total signal flux if the receiving bandwidth equals or is greater than the bandwidth of the signal

Wm^-2 Hz^-1 (or W/m² Hz) - spectral flux density (see jansky)

x radiation - electromagnetic radiation in the range of approximately 0.05-100Å.

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