Astronomical Explorations/Astronomical Explorations.iso/stars/testi/gloss

Text File | 1994-08-10 | 10KB | 239 lines

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Absolute zero. Temperature at which all molecules stop moving and
for which there is nothing lower: it corresponds to 273.18 degrees
Celsius.
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Asteroid. Rocky body, smaller than a planet, that orbits around the
Sun. Most asteroids are located in a belt between the orbit of Mars
and Jupiter.
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Astronomy. Branch of science that studies the universe beyond the
Earth's atmosphere.
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Atmosphere. Gaseous shell that surrounds a planet; its name comes
from the Greek word atmos, i.e. steam, smoke. The term atmosphere
also indicates the unit of measurement of pressure, equal to the weight
of a column of mercury of 760 mm on the surface of 1 sq.cm. at a
temperature of 0 degrees C.
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Atom. The smallest unit of a chemical element. It contains a nucleus
with a positive electric charge, consisting of particles called neutrons
and protons, and by one or more electrons, orbiting around the
nucleus, with a negative charge. Overall, the atom has no charge.
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Atomic particle. Minuscule part of matter that, among other things,
includes one of the constituents of the atom, i.e. an electron, proton or
neutron.
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Axis. Imaginary line around which a body rotates.
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Big Bang. Huge primeval explosion which created all matter and
therefore the universe.
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Binary star. Star that is part of a pair of stars which orbit around a
common center.
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Black hole. Extremely massive object, perhaps a collapsed star, whose
gravitational field is so intense that not even light can escape. For this
reason it is invisible.
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Comet. Small celestial body composed of ice and dust that orbits
around the Sun. When it gets close to the Sun, it develops a long
gaseous tail that is always oriented by the solar radiation along the
direction of the straight line that joins the Sun with the nucleus and
in the sense that moves away from the star.
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Compound. Substance formed by the chemical combination of two or
more elements. Water, for example, is a compound of hydrogen and
oxygen.
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Cosmic rays. Atomic and subatomic particles which travel in space at
high speed irradiated by the Sun or by other stars.
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Crust. The thin outermost layer consisting of rocks of a moon or a
planet.
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Density. A measurement of how matter is condensed in a given space.
The density of water is the reference value and is equal to 1.
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Doppler Effect. Change in frequency of sound or light waves caused
by the relative motion of the body that emits them or by the motion
of the observer.
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Eclipse. Total or partial occultation of the light emitted by a celestial
body by the shadow cone of another body.
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Ecliptic. Apparent motion of the Sun in the sky or the plane in which
the Earth's orbit lies.
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Electromagnetic spectrum. The entire arc of the radiation emitted by a
body, of which light is only one part. It ranges from high-energy
gamma rays to low-energy radio waves.
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Electron. Negatively charged particle with a very small mass that
orbits around the nucleus of an atom or that is free in space and in
stars.
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Element. The simplest chemical form, consisting of the same type of
atoms. Oxygen, iron and hydrogen are some of the 106 known
elements.
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Energy. Ability of a body to produce work, i.e. motion, heat or
chemical reactions.
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Frequency. The rhythm with which a light or sound wave passes a
certain point, measured in cycles per second or hertz. Short waves
have a high frequency; long waves a low frequency.
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Galaxy. A group of billions of stars bound to each other by
gravitational attraction and arranged in space in the shape of a disk or
a more or less tight spiral. The group to which our Sun belongs is also
called the Milky Way.
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Globular cluster. Dense group of stars which may include several
thousand to several million stars.
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Gravitation. The force with which two masses attract each other and
which is directly proportional to the distance between two bodies.
Even though it is the weakest force known in nature, in reality, on an
astronomical scale, it is the most dominant because it determines the
motion of the planets, stars and galaxies.
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Gravity. The force which, at the surface of a planet or another body,
attracts all masses towards its center.
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Greenhouse effect. Heating produced by trapping short
electromagnetic waves (light) and by their transformation into long
electromagnetic waves (heat).
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Interstellar dust. Small solid particles of matter distributed among the
stars and sometimes condensed into clouds.
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Interstellar gas. Matter in the gaseous state distributed among the stars,
consisting mainly of hydrogen and sometimes concentrated into
clouds.
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Ion. Atom that has lost or acquired one or more electrons acquiring
either a positive or negative charge.
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Light-year. Astronomical unit of measurement that corresponds to the
distance traveled by light in one Earth year. Since light travels at a
speed of approximately 300 000 kilometers per second, one light-year
is equal to 9 460 500 000 000 kilometers.
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Magnetosphere. Area of space within which a magnetic field operates.
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Mass. The quantity of matter contained in a body.
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Matter. Formed by atomic particles, atoms and molecules, it is the
fundamental substance of the universe. Matter exists in four states:
solid, liquid, gas and plasma.
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Meteor. A luminous streak (also known as a "shooting star") produced
by a meteoroid that crosses the Earth's atmosphere and completely
burns up.
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Meteorite. Meteoroid that survives after crossing the Earth's
atmosphere and reaches the surface without completely burning up.
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Meteoroid. Solid body smaller than an asteroid that orbits around the
Sun.
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Molecule. The smallest quantity of a compound that retains all its
chemical properties. For example, one molecule of water consists of
two atoms of hydrogen and one atom of oxygen.
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Nebula. Mass of gas and interstellar dust that appears in the sky as a
dark or luminous spot if one or more stars illuminate it.
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Neutrino. Atomic particle with no mass and electric charge that
travels at the imaginary speed of light.
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Neutron. Atomic particle with a very high mass but no electric charge.
Neutrons are present in the nuclei of all atoms except in hydrogen
(which has only one proton and one electron).
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Neutron star. Body consisting of very densely packed neutrons. This
type of star is what remains after the explosion of a supernova.
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Nova. Star that suddenly increases in brightness hundreds of times
and then diminishes.
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Nuclear fusion. Process of transforming matter into energy. The
nucleii of light atoms are held together (fused) to form heavier
nucleii, releasing enormous amounts of energy.
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Orbit. Trajectory described by the motion of a celestial body around
another body.
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Photosphere. Area that is the apparent portion of a star. The solar
photosphere has a temperature of around 6 000 degrees.
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Photosynthesis. Process according to which plants utilize light energy
to process the chemical substances necessary for their survival.
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Planet. Rotating body without its own luminosity that is kept in orbit
by the gravitational attraction of a star.
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Plasma. A gas formed by electrons and ions, also called "fourth state
of matter", because its temperature is too high to permit atoms to
form.
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Polar lights. A wall or wavy luminous band visible in the sky
especially in the areas near the Earth's poles. Called borealis or
austral, depending on whether they form in the northern or southern
hemisphere, the lights are produced by the excitation of the gas atoms
of the ionosphere by streams of electrons emitted by the Sun.
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Pressure. A measurement of the force exerted on a surface.
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Proton. Name of the nucleus of the hydrogen atom considered as an
elementary particle. Along with the neutron, it is the fundamental
part of the atomic nucleus of any element.
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Pulsar. Neutron star that rotates rapidly around itself and emits a
strong beam of radiation.
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Quasar. Mysterious object whose nam