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Right Ascension: (RA) the angular distance of a celestial object measured in hours, minutes, and seconds along
the Celestial Equator eastward from the Vernal Equinox.
S -
Schmidt Telescope Rated the most important advance in optics in 200 years, the Schmidt telescope combines
the best features of the refractor and reflector for photographic purposes. It was invented in
1930 by Bernhard Voldemar Schmidt (1879-1935).
Sidereal Rate This is the angular speed at which the Earth is rotating. Telescope tracking motors drive
the telescope at this rate. The rate is 15 arc seconds per second or 15 degrees per hour.
T -
Terminator The boundary line between the light and dark portion of the moon or a planet.
U -
Universe The totality of astronomical things, events, relations and energies capable of being
described objectively.
V -
Variable Star A star whose brightness varies over time due to either inherent properties of the star or
something eclipsing or obscuring the brightness of the star.
W -
Waning Moon The period of the moon's cycle between full and new, when its illuminated portion is
decreasing.
Waxing Moon The period of the moon's cycle between new and full, when its illuminated portion is
increasing.
Z -
Zenith The point on the Celestial Sphere directly above the observer.
Zodiac The zodiac is the portion of the Celestial Sphere that lies within 8 deg on either side of the
Ecliptic. The apparent paths of the Sun, the Moon, and the planets, with the exception of
some portions of the path of Pluto, lie within this band. Twelve divisions, or signs, each 30
deg in width, comprise the zodiac. These signs coincided with the zodiacal constellations
about 2,000 years ago. Because of the Precession of the Earth's axis, the Vernal Equinox
has moved westward by about 30 deg since that time; the signs have moved with it and
thus no longer coincide with the constellations.