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Source edition 1965. Please read the Introduction
to find out about this dictionary and our plans for it. Caution, many entries have not been updated since the 1965 edition.
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- That point of the celestial
sphere vertically overhead.
- The point 180 degrees from the zenith is called the nadir.
- Of or pertaining to the zenith.
- zenith attraction
- The effect of the earth's gravity on a meteoric body,
which increases the velocity and moves the radiant toward
- zenith distance
- Angular distance from the zenith; the arc of a vertical
circle between the zenith and a point on the celestial
sphere, measured from the zenith through 90 degrees, for bodies above the
- This is the same as colatitude with reference to the celestial
- Referring to positions on Jupiter measured in latitude from
Jupiter's equator and in longitude
from a reference meridian.
- zero gravity = weightlessness.
- zero-g = weightlessness.
- zero launch
- The launch of a rocket or aircraft by a zero-length
- zero-length launcher
- A launcher that
holds a vehicle in position and releases the rocket simultaneously at two
points so that the buildup of thrust, normally
rocket thrust, is sufficient to take the missile or vehicle directly into the
air without need of a take-off run and without imposing a pitch rate release.
- The term is not normally applied to a pad used for a vertical
- zero-length rocket
- A rocket
with sufficient thrust to launch a vehicle directly into the air.
- Said especially of a rocket used to launch an aerodynamic vehicle.
- zero-lift chord
- A chord
taken through the trailing edge of an airfoil in the
direction of the relative wind when the airfoil is at a zero-lift angle of
- zeta machine
- An experimental thermonuclear
device which generates a plasma inside a
torus and employs the pinch
effect for heating and compression.
- zip fuel
- A boron-base high-energy liquid
- The band of the sky extending 8 degrees either side of the ecliptic.
- The Sun, Moon, and navigational planets are always within this band,
with the occasional exception of Venus. The zodiac is divided into 12 equal
parts, called signs, each part being named for the principal constellation
originally within it.
- zodiacal counterglow = gegenschein.
- zodiacal light
- A faint cone of light extending upward from the horizon in the direction
of the ecliptic
(zodiac). It is seen from tropical latitudes for a few hours after sunset or
- The spectrum of the zodiacal light is similar to that of sunlight, so
it has been suggested that it is due to the scattering of sunlight by
extraterrestrial dust particles. Some scattering is also due to electrons.
- zone time
- See time.
- z-time = Greenwich mean time.
- Zurich number = relative sunspot number