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telescope
a tubed instrument used to brighten and magnify the view of astronomical objects (telescopes gather more light than the eye)
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tera
a trillion (1,000,000,000,000 in American usage)
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terminator
the boundary on a planet or moon separating the illuminated side from the unilluminated.
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terrestrial
of or relating to Earth
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terrestrial planet
a small, rocky planet such as Mercury, Venus, Earth, and Mars
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thermal radiation
electromagnetic radiation emanating from any object not at absolute zero
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tidal force
the difference in gravitational force between two points on an object caused by the gravity of another object; the tidal force often leads to a deformation of an object
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tides
the distortion of a body caused by the gravitational influence of another body
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transit
the passage of a smaller body in front of a larger body; also, the passage of a celestial body across an observer’s meridian
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transparency
the clarity of the sky
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tremolite
a common mineral in some metamorphic rocks, composed mainly of calcium and magnesium; it occurs from the conversion of dolomite (a sedimentary rock), silica, and water
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trillion
1,000,000,000,000 (in American usage)
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tropical year
the time it takes Earth to revolve around the sun with respect to the vernal equinox
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true field of view
the angle of sky seen through an eyepiece when it is attached to a telescope; the true field equals the apparent field divided by the magnification
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type Ia supernova
the explosion of a white dwarf that occurs when it accretes enough mass from a companion star to go above the Chandrasekhar limit
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type II quasars
a quasar enshrouded in gas and dust that emits very little visibile light, however, is easily seen in the infrared and x-ray region of the electromagnetic spectrum
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type II supernova
the explosion of a massive star that occurs when its core runs out of nuclear fuel; these explosions leave behind a neutron star or a black hole
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