Accretion
Disks - A disk of interstellar material surrounding a celestial
object with an intense gravitational field, such as a black hole.
Asteroids - Any of numerous small celestial bodies that revolve
around the sun, with orbits lying chiefly between Mars and Jupiter
and characteristic diameters between a few and several hundred
kilometers.
Astrology - The study of the positions and aspects of celestial
bodies in the belief that they have an influence on the course
of natural earthly occurrences and human affairs.
Astronomy - The scientific study of matter in outer space, especially
the positions, dimensions, distribution, motion, composition,
energy, and evolution of celestial bodies and phenomena.
Astronomer - One who specializes in astronomy.
Atmosphere - The gaseous mass or envelope surrounding a celestial
body, especially the one surrounding the earth, and retained by
the celestial body's gravitational field.
Black Hole - An area of space-time with a gravitational field
so intense that its escape velocity is equal to or exceeds the
speed of light.
Brown Dwarf - A celestial body that resembles a star but does
not emit light because it is too small to ignite internal nuclear
fusion. The planet Jupiter is a small brown dwarf.
Celestial Equator - A great circle on the celestial sphere in
the same plane as the earth's equator.
Celestial Sphere - An imaginary sphere of infinite extent with
the earth at its center on which the stars, planets, and other
heavenly bodies appear to be located.
Comets - A celestial body, observed only in that part of its
orbit that is relatively close to the sun, having a head consisting
of a solid nucleus surrounded by a nebulous coma up to 2.4 million
kilometers (1.5 million miles) in diameter and an elongated curved
vapor tail arising from the coma when sufficiently close to the
sun. Comets are thought to consist chiefly of ammonia, methane,
carbon dioxide, and water.
Contraction - To be reducde in size by drawing together; to shrink.
Convection - Heat transfer in a gas or liquid by the circulation
of currents from one region to another.
Core - The central or innermost part; for example, of planets
or stars.
Corona - faintly colored luminous ring appearing to surround
a celestial body visible through a haze or thin cloud, especially
such a ring around the moon or sun, caused by diffraction of light
from suspended matter in the intervening medium.
Ecliptic - The intersection plane of the earth's orbit with the
celestial sphere, along which the sun appears to move as viewed
from the earth.
Ellipse - a plane curve, The locus of points for which the sum
of the distances from each point to two fixed points is equal.
Event Horizon - The region, usually described as spherical, marking
the outer boundary of a black hole, inside which the gravitational
force is strong enough to prevent matter or radiation from escaping.
Extra Terrestrial - Originating, located, or occurring outside
Earth or its atmosphere.
Galactic Center - The center of a galaxy; in the Milky Way Galaxy,
the galactic center is thought to be a black hole.
Galaxy - Any of numerous large-scale aggregates of stars, gas,
and dust that constitute the universe, containing an average of
100 billion (1011) solar masses and ranging in diameter from 1,500
to 300,000 light-years.
Gravity - The natural force of attraction exerted by a celestial
body, such as Earth, upon objects at or near its surface, tending
to draw them toward the center of the body.
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Horizon
- The apparent intersection of the earth and sky as seen by an
observer.
Magnetic Field - A condition found in the region around a magnet
or an electric current, characterized by the existence of a detectable
magnetic force at every point in the region and by the existence
of magnetic poles.
Mass - A property of matter equal to the measure
of an object's resistance to changes in either the speed or direction
of its motion. The mass of an object is not dependent on gravity
and therefore is different from but proportional to its weight.
Meteor - A bright trail or streak that appears in
the sky when a meteoroid is heated to incandescence by friction
with the earth's atmosphere.
Meteoroid - A solid body, moving in space, that
is smaller than an asteroid and at least as large as a speck of
dust.
Molecular Clouds - a type of interstellar cloud
whose density and size permits the formation of molecules, most
commonly molecular hydrogen (H2).
Moons - A natural satellite revolving around a planet.
Planets - A nonluminous celestial body larger than an asteroid
or comet, illuminated by light from a star, such as the sun, around
which it revolves. In the solar system there are nine known planets:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune,
and Pluto.
Orbit - The path of a celestial body or an artificial satellite
as it revolves around another body.
Planetary Nebula - A nebula, such as the Ring Nebula, consisting
of a hot, blue-white, central star surrounded by an envelope of
expanding gas.
Protoplanet - the first stage in planetary development.
Protostar - any early stage in the formation of a star when an
interstellar cloud of gas and dust starts to collapse but before
nuclear synthesis has begun at its core.
Red Giant - A star of great size and brightness that has a relatively
low surface temperature.
Satellite - A celestial body that orbits a planet; a moon.
Singularity - A point in space-time at which gravitational forces
cause matter to have infinite density and infinitesimal volume,
and space and time to become infinitely distorted.
Solar Wind - A stream of high-speed, ionized particles ejected
primarily from a star's corona.
Star - A self-luminous celestial body consisting of a mass of
gas held together by its own gravity in which the energy generated
by nuclear reactions in the interior is balanced by the outflow
of energy to the surface, and the inward-directed gravitational
forces are balanced by the outward-directed gas and radiation
pressures.
Supernova - A rare celestial phenomenon involving the explosion
of most of the material in a star, resulting in an extremely bright,
short-lived object that emits vast amounts of energy.
Terrestrial - Of or relating to the earth or its inhabitants.
Universe - All matter and energy, including the earth, the galaxies,
and the contents of intergalactic space, regarded as a whole.
Wavelength - The distance between one peak or crest of a wave
of light, heat, or other energy and the next corresponding peak
or crest.
White Dwarf - The remnant of a star that has collapsed, having
an extremely dense state with no empty space between its atoms,
but not reaching the extremely dense state of a neutron star or
black hole.
X-ray Radiation – a stream of relatively high-energy photons
having wavelengths in the approximate range from 0.01 to 10 nanometers.
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