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Absolute zero the temperature at which substances possess no thermal energy, equal to -273.15°C, or -459.67°F.
Array to place or set in order: arranged.
Asterism a small group of stars.
Astronomer one who is skilled in astronomy or who makes observations of celestial phenomena.
Astrophysics a branch of astronomy dealing with the physical and chemical constitution of the celestial bodies.
Atmosphere a gaseous mass enveloping a heavenly body (as a planet) b: the whole mass of air surrounding the earth.
Atom one of the minute indivisible particles of which according to ancient materialism the universe is composed.
Celestial of or relating to the sky or visible heavens (a ~ body).
Celestial body a body located in the sky or visible heavens.
Celestial pole one of the two points on the celestial sphere around which the diurnal rotation of the stars appears to take place.
Chargeless without electrical charge (not positive or negative, but neutral).
Compound composed of or resulting from union of separate elements, ingredients, or parts, SPECIFICALLY: composed of united similar elements especially of a kind usually independent.
Corona a usually colored circle often seen around and close to a luminous body (as the sun or moon) caused by diffraction produced by suspended droplets or occasional particles of dust b: the tenuous outermost part of the atmosphere of the sun appearing as a gray halo around the moon's black disk during a total eclipse of the sun.
Dark matter [see related section] nonluminous (not emitting light or visible) material that cannot be detected by observing the sky, but whose existence is suggested by certain theories.
Density the quantity per unit volume, unit area, or unit length.
Dimensionless unmeasurable in any way.
Element any of more than 100 fundamental substances that consist of atoms of only one kind and that singly or in combination constitute all matter.
Equator a circle or circular band dividing the surface of a body into two usually equal and symmetrical parts.
Fusion the process of blending by melting together b: becoming fluid with heat.
Galaxy [see related section] one of billions of systems each including stars, nebulae, star clusters, globular clusters, and interstellar matter that make up the universe.
Gravity the gravitation attraction of a mass (such as the earth) for bodies at or near its surface.
Horizon the point at which an object entering a black hole cannot return; also the edge of a black hole 2: the apparent junction of earth and sky.
Hydrogen a nonmetallic element that is the simplest and lightest of the elements, and is normally a colorless odorless highly flammable diatomic (two atoms) gas.
Index of refraction The ratio of the speed of light in a vacuum to the speed of light in a medium under consideration.
Infinite a subject to no limitation or external determination 2: extending indefinitely; endless.
Infrared lying outside the visible spectrum at its red end - used of thermal radiation of wavelengths longer than those of visible light.
Kelvins the thermometric scale on which the unit of measurement equals the centigrade (also known as Celsius) degree and according to which absolute zero is 0°, the equivalent of -273.16°C.
Latitude angular distance north or south from the earth's equator measured through 90 degrees.
Light-year a unit of length in interstellar astronomy equal to the distance that light travels in one year in a vacuum or 5,878,000,000,000 miles.
Longitude the arc or portion of the earth's equator intersected between the meridian of a given place and the prime meridian (as from Greenwich, England) and expressed either in degrees or in time.
MACHOs short for MAssive Compact Halo Objects, which are non-nuclear objects that normally surround galaxies.
Matter a substance of which a physical object is composed b: a substance that constitutes the observable universe and together with energy forms the basis of objective phenomena.
Molecule the smallest particle of an element or compound capable of retaining chemical identity with the substance in mass.
Neutrino an uncharged elementary particle with zero rest mass.
Neutron an uncharged (neutral) elementary particle, stable when bound in an atomic nucleus and having a mean lifetime of about 12 minutes as a free particle (note: the neutron is found in all known elementary nuclei except for the hydrogen nuclei).
Neutron star [see related section] a rapidly spinning, extremely dense star composed of mainly neutrons.
Northern Hemisphere the area above (north) the equator.
Nuclear radiation spontaneous disintegration of atomic nuclei by the emission of subatomic particles called alpha particles and beta particles, or of electromagnetic rays called X rays and gamma rays.
Nucleus the positively charged central region of an atom, composed of protons and neutrons and containing almost all of the mass of the atom.
Nuclei a term describing more than one nucleus.
Numbers here is the ascending order of names of numbers: hundred, thousand, million, billion, trillion, quadrillion, quintillion, sextillion, septillion, octillion, nonillion, decillion, undecillion, duodecillion, tredecillion, quat(t)uordecillion, quindecillion, sexdecillion, septendecillion, octodecillion, novemdecillion, vigintillion.
Optical telescope [see related section] a telescope in which mirrors are used to reflect an image to the observer.
Physics a science that deals with matter and energy and their interactions in the fields of mechanics, acoustics, optics, heat, electricity, magnetism, radiation, atomic structure, and nuclear phenomena.
Physicist a specialist in physics.
Radio telescope a radio receiver-antenna combination used for observation in radio astronomy.
Radioactivity the property possessed by some elements (as uranium) of spontaneously emitting alpha or beta rays and sometimes also gamma rays by the disintegration of the nuclei of atoms.
Redshift [see related section] An increase in the wavelength of radiation emitted by a celestial body due to the Doppler effect.
Satellite a moon revolving around a larger planet b: a man-made object rocketed into orbit around the earth, the moon, etc.
Solar granules turbulent cells in the photosphere of sun, giving the sun an irregular, mottled appearance.
Solar mass a direct relation in how much mass an object has compared to the sun (for example, if a star has a mass of 1.4 solar masses, then it is 1.4 x mass of the sun) .
Solar system [see related section] the sun with the group of celestial bodies that are held by its attraction and revolve around it.
Southern Hemisphere the area below (south) the equator.
Spectrometer an instrument used to measure wavelengths or indexes of refraction.
Spectroscopy the study of sky or heavens using a spectrometer.
Spectrum an array of the components of an emission or wave separated and arranged in the order of some varying characteristic (as wavelength, mass, or energy) (such as the light spectrum).
Sphere a globular body: ball b: planet, star.
Spherical having the form of a sphere of one of its segments.
Telescope a usually tubular optical instrument for viewing distant objects by means of the refraction of light rays through a lens of reflection that is a concave mirror b: a tube that contains a mirror (or mirrors) that help magnify an object that is far away.
Thermal radiation radiation of or relating to, or caused by heat.
Thermonuclear reaction a reaction of or relating to the transformation in the nucleus of atoms of low atomic weight (as hydrogen) that require a very high temperature for their inception (beginning), as in the sun.
Universe [see related section] the whole body of things and phenomena observed or postulated.
Unmanned having no humans aboard.
Wavelength the distance between one peak or crest of a wave, as of light or sound, and the next corresponding peak or crest.
White dwarf a whitish star of low luminosity, small size, and very great density.
WIMPs short for Weakly Interacting Massive Particles, which are theorized particles 10 to 100 times the size of protons, could account for lots of the dark matter.
X-ray a relatively high-energy photon with a very short wavelength.
Zenith the point on the celestial sphere that is directly above the observer 2: the highest point above the observer's horizon attained by a celestial body.
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