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 Introduction to Astronomy
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 Glossary: Climate Change
 Glossary: Astronomy
 Glossary: Life in Universe
 


    Glossary of Terms - G to L
    Index: A to F | G to L | M to R | S to Z


    Gaia hypothesis - (n.)

    The idea, first proposed by James Lovelock, that the organisms in the entire biosphere of Earth interact with each other and their physical environment to stabilize the Earth's environmental conditions over a narrow range.

    gain stability - (n.)

    Crudely defined by AG/G = 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.

    galactic cluster - (n.)

    An asymmetric type of collection of stars that shared a common origin.

    galaxy - (n.)

    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.

    Galilean satellites - (n.)

    The four brightest satellites of Jupiter, discovered by Galileo.

    gamete - (n.)

    Haploid female (egg) and male (sperm) sex cells, in animals formed by meiosis and in plants by mitotic division of haploid cells derived from meiotically produced spores.

    gamma ray - (n.)

    High-energy electromagnetic particle or photon, especially as emitted by a nucleus in its transition from one energy level to another. Radiation whose wavelength is less than one Angstrom is usually considered to be gamma-ray radiation.

    gas - (n.)

    The state of matter in which the substance maintains neither shape nor volume.

    gas chromatography - (n.)

    A chemical technique for separating gas mixtures, in which the gas is passed through a long column containing a fixed absorbent phase that separates the gas into its component parts.

    gegenschein - (n.)

    The diffuse glowing spot, seen on the ecliptic opposite the sun's direction, created by sunlight reflected off of interplanetary dust. ~ See Also: zodiacal light.

    gene - (n.)

    A segment of DNA containing hereditary information for production of a protein or RNA (ribonucleic acid) molecule.

    gene duplication - (n.)

    The process by which multiple copies of genes are biosynthesized.

    gene pool - (n.)

    Total amount of information in all the genes of all the reproductive members of a biological population at any given time.

    genetic code - (n.)

    "The set of equivalences between proteinogenic amino acids and the nucleotide triplets, or codons, that code for the amino acids in messenger RNAs. ~ See Also: Amino acid, Codon, Messenger RNA, Translation.



    Index: A to F | G to L | M to R | S to Z


    Gaia hypothesis - (n.)

    The idea, first proposed by James Lovelock, that the organisms in the entire biosphere of Earth interact with each other and their physical environment to stabilize the Earth's environmental conditions over a narrow range.

    gain stability - (n.)

    Crudely defined by AG/G = 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.

    galactic cluster - (n.)

    An asymmetric type of collection of stars that shared a common origin.

    galaxy - (n.)

    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.

    Galilean satellites - (n.)

    The four brightest satellites of Jupiter, discovered by Galileo.

    gamete - (n.)

    Haploid female (egg) and male (sperm) sex cells, in animals formed by meiosis and in plants by mitotic division of haploid cells derived from meiotically produced spores.

    gamma ray - (n.)

    High-energy electromagnetic particle or photon, especially as emitted by a nucleus in its transition from one energy level to another. Radiation whose wavelength is less than one Angstrom is usually considered to be gamma-ray radiation.

    gas - (n.)

    The state of matter in which the substance maintains neither shape nor volume.

    gas chromatography - (n.)

    A chemical technique for separating gas mixtures, in which the gas is passed through a long column containing a fixed absorbent phase that separates the gas into its component parts.

    gegenschein - (n.)

    The diffuse glowing spot, seen on the ecliptic opposite the sun's direction, created by sunlight reflected off of interplanetary dust. ~ See Also: zodiacal light.

    gene - (n.)

    A segment of DNA containing hereditary information for production of a protein or RNA (ribonucleic acid) molecule.

    gene duplication - (n.)

    The process by which multiple copies of genes are biosynthesized.

    gene pool - (n.)

    Total amount of information in all the genes of all the reproductive members of a biological population at any given time.

    genetic code - (n.)

    "The set of equivalences between proteinogenic amino acids and the nucleotide triplets, or codons, that code for the amino acids in messenger RNAs. ~ See Also: Amino acid, Codon, Messenger RNA, Translation.



    Index: A to F | G to L | M to R | S to Z


    genetic drift - (n.)

    The evolutionary spread of random fluctuations (or "walk") of gene frequencies from generation to generation that occur in small populations. ~ See Also: Mutation, Natural selection.

    genome - (n.)

    The totality of all genes in any organism.

    genotype - (n.)

    Equivalent to genome, this term is used in opposition to phenotype to designate the hidden genetic information responsible for the expressed properties of an organism (phenotype). ~ See Also: Phenotype.

    genus - (n.)

    Taxonomic category ranking below a family and above a species.

    geochromatography - (n.)

    A process by which finely divided minerals in the Earth itself have separated out organic compounds, just as chemists use chromatography to do the same thing in the laboratory.

    geothermal energy - (n.)

    Energy derived from the heat of Earth's interior.

    germination - (n.)

    The initiation of development in a dormant plant embryo.

    giant planets - (n.)

    Jupiter, Saturn, Uranus, and Neptune.

    giant star - (n.)

    A type of star brighter than main sequence stars of the same spectral type.

    gibbous moon - (n.)

    The phases between half moon and full moon.

    giga - (n.)

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

    glucose - (n.)

    A six-carbon sugar, C6H12O6, the universal fuel of life; often abbreviated CH2O.

    Golgi - (n.)

    From the name of the Italian scientist who discovered it, a part of the cytomembrane system, consisting of stacked, flat, membranous sacs, involved in the processing of newly synthesized lysosomal and secretory proteins. ~ See Also: Cytomembrane system, Endoplasmic reticulum, Lysosome, Protein, Secretion.

    Gondwanaland - (n.)

    The late Paleozoic to early Mesozoic supercontinent composed of the land masses of South America, Africa, Madagascar, India, and Antarctica.



    Index: A to F | G to L | M to R | S to Z


    gram - (n.)

    A unit of mass equal to the quantity' of mass contained in one cubic centimeter of water.

    gram-negative bacteria - (n.)

    Bacteria with two outer membranes that react negatively to a test devised by the Danish bacteriologist Hans Christian Joachim Gram.

    gram-positive bacteria - (n.)

    Bacteria with a single outer membrane that react positively to the Gram test. ~ See Also: Gram-negative bacteria.

    greenhouse effect - (n.)

    A warming of the Earth's surface and lower layers of the atmosphere caused by interaction of solar radiation with atmospheric gases (mainly carbon dioxide, methane, and water vapor) and its conversion to heat because it is transparent to incoming visible radiation but opaque to the infrared radiation that is emitted by the surface of the planet.

    group, geologic - (n.)

    A major category in the stratigraphic classification of rocks ranking above the formation and below the supergroup.

    guanine (G) - (n.)

    One of the four nitrogenous bases in the nucleotides of DNA and RNA.

    gunflint formation - (n.)

    A fossiliferous 2,100Ma-old geologic unit of southern Ontario, Canada.

    gymnosperm - (n.)

    Any member of the taxonomic group (Gymnospermae) that consists of plants having naked seeds such as conifers, cycads, and Ginkgo.

    half life - (n.)

    The period of time needed for half of the radioactive isotopes in a sample to decay to daughter atoms.

    haploid - (n.)

    The character of a cell having a single set of chromosomes; eg. sperm or egg. ~ See Also: Diploid.

    heat - (n.)

    A measure of a quantity of energy; of how much energy a sample contains.

    hematite - (n.)

    A mineral, the iron oxide Fe2O3.

    heme - (n.)

    A porphyrin derivative with a central iron atom, involved, when combined with a protein (hemoprotein), in electron transfer, oxygen transport, and related reactions. ~ See Also: Chlorophyll, Cytochrome, Electron transfer.

    heredity - (n.)

    The transmission of genetic factors that determine individual characteristics from one generation to the next.



    Index: A to F | G to L | M to R | S to Z


    hermaphrodite - (n.)

    An organism with both male and female sex organs.

    heterotrophy - (n.)

    Literally, other-feeding; the condition of an organism that is not able to obtain nutrients by synthesizing non organic materials from the environment, and that therefore must consume other life forms to obtain the organic products necessary for life e.g., animals, fungi, most bacteria.

    homeostasis - (n.)

    The ability of living organisms to keep constant certain of their physical or chemical properties by self-regulation.

    horizontal gene transfer - (n.)

    The transfer of genes from one organism to another, as opposed to vertical gene transfer, from parent to offspring.

    hormone - (n.)

    A chemical transmitter transported by the blood stream or some other humoral connection from the cells that secrete it to the cells on which it acts. ~ See Also: Chemical transmitter.

    hydrocarbon - (n.)

    Any of a diverse group of organic compounds composed of hydrogen and carbon.

    hydrogen - (n.)

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

    hydrogen bond - (n.)

    The dipole interaction between a hydrogen atom bonded to F, O, or N in a donor molecule and an F, 0, or N atom in a receptor molecule.

    hydrogenosome - (n.)

    A membrane-bounded cytoplasmic organelle found in some protists and fungi, and characterized by the ability to produce molecular hydrogen : Possibly of endosymbiont origin. ~ See Also: Endosymbiont.

    hydrogen source - (n.)

    A chemical source of hydrogen atoms (electrons) that during photosynthesis combine with carbon dioxide to form glucose sugar.

    hydrophilic - (n.)

    The water-binding property common to all electrically charged or polarized substances (including water itself). ~ See Also: Amphiphilic, Hydrophobic.

    hydrosphere - (n.)

    The oceans, seas, rivers, and lakes of the Earth.

    hydrothermal vent - (n.)

    A deep ocean vent at which magma-heated and mineral-laden water spews out at a high rate. The water, heated to temperatures of more than 300°C, remains liquid because of the high pressure.

    hyperthermophile - (n.)

    Any of various prokaryotic microorganisms, such as diverse members of the Archaea, that survive and grow in exceptionally high temperature (>80° C) environments.



    Index: A to F | G to L | M to R | S to Z


    hypotheses - (n.)

    Guesses that can be tested by experiment.

    igneous - (n.)

    Previously molten rocks that have crystallised (e.g., basalt and granite).

    index fossil - (n.)

    Any of diverse fossils thatóbecause they are easily recognizable, exist over a relatively short period of geologic time, and are widespreadócan be used to determine the age of rock strata in which they are preserved.

    indigenous - (n.)

    Having originated in a particular setting.

    inorganic chemistry - (n.)

    The study of the compounds of all elements other than carbon.

    intron - (n.)

    Or intervening sequence, a gene segment that is transcribed but is subsequently excised from the resulting RNA and, therefore, is not expressed. ~ See Also: Exon, RNA splicing, Split genes.

    invertebrate - (n.)

    Any of diverse animals that lack backbones; "lower metazoans."

    isomers - (n.)

    Compounds that have the same molecular formula but different structural formulas and properties.

    isotopes - (n.)

    Different forms of an element that have the same number of protons in their nuclei, and thus the same atomic number, but that have different numbers of neutrons and thus different atomic masses. There are two kinds of isotopes, stable and unstable. Isotopes that are unstable are called radioactive and disintegrate at a constant decay rate. Examples of stable isotopes include carbon-12 and carbon-13. Carbon-14, and uranium-238 and -235, are examples of unstable isotopes.

    isotopic date - (n.)

    Age of a rock (or organic substance less than 60,000 years old) determined by measurement of the ratio of a parent isotope to one of the products of its radioactive decay.

    Kardashev cultures - (n.)

    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 111, the power output of a galaxy.

    Kelvin - (n.)

    A unit of temperature equal to one one-hundredth of the difference between the freezing and boiling points of water, and used in a scale whose zero point is absolute zero. A Kelvin is usually denoted by K.

    lateral gene transfer - (n.)

    Natural processes by which some of the genes of an organism can be transferred into the genome of another species.

    law of conservation of mass - (n.)

    Matter is neither created nor destroyed during a chemical change.



    Index: A to F | G to L | M to R | S to Z


    law of superposition - (n.)

    The geologic rule that, in a sequence of undeformed strata, the oldest rock layer is at the bottom and each layer upward is progressively younger.

    levo isomer - (n.)

    A "left-handed" isomer.

    life era - (n.)

    Era in the history of the Universe when life emerges as the dominant element.

    light-harvesting pigment - (n.)

    Organic compounds, such as chlorophyll and bacteriochlorophyll, that absorb light energy in photosynthesis.

    limestone - (n.)

    A kind of sedimentary rock consisting mainly of calcium carbonate minerals.

    lipid - (n.)

    A fatty substance from animal or plant cells that is soluble in nonpolar solvents and insoluble in water.

    liquid - (n.)

    A state of matter in which the substance assumes the shape of its container, flows readily, and maintains a fairly constant volume.

    liter - (n.)

    Unit of volume equal to a cube with sides 10 cm.

    lithosphere - (n.)

    The layer in the earth, moon, and terrestrial planets that includes the crust and the outer part of the mantle.



    Index: A to F | G to L | M to R | S to Z

 


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