Glossary for Stargazers Albedo The ratio of a bodies diffuse reflectance to to the total light falling on it. (lightness or darkness).
Aphelion The point most distant from the sun, of an object in  solar orbit.
Apogee the point most distant from the earth of an object orbiting the earth.
Astronomical Telescope basically consists of  an objective and an eyepiece thus giving an inverted image.
(1)Reflecting telescope is where the objective component is a mirror.
(2)Refracting telescope is where the objective component is a lens.
(3)Catadioptric telescope, a combination of 2 mirrors plus a  correcting lens in front of the mirrors.
Astronomical Unit (A.U.)   unit of length equal to the distance between the sun and the earth , or about
150 million km.
Celestial Meridian A plane passing through both celestial poles projected on the celestial sphere.
Celestial Sphere an imaginary sphere surrounding the universe on which terrestrial, solar, and celestial
coordinates are projected.  When these projections are terrestrial, they are preceded by the word Celestial
(e.g. Celestial North Pole).
Comet A solar system object with an orbit far more eccentric than a planet. On approaching the sun, the
comet usually develops a tail as the icy core melts and vaporizes.
Conjunction when  two solar system objects  have the same celestial longitude.
Culmination A celestial object is said to culminate when it crosses your meridian (either upper or lower).
Declination The angle in degrees of a celestial object measured from  the Celestial Equator to the
Celestial Pole (+ in the northern hemisphere and - in the southern).
Double Star  Two stars appearing very close togeather. If related they are called physical doubles; If unrelated, they
are called optical doubles.
Ecliptic the plane of the earth’s solar orbit projected on the Celestial Sphere.
Elongation The angular distance between a planet and the sun.
Equinoxes The 2 points where the ecliptic intersects the celestial equator or where the sun crosses the
celestial equator. It is the vernal equinox ( March 21) when the sun crosses from south to north and
autumnal (Sept 23) when the sun crosses from north to south
Galaxy Our own Milky Way when capitalized but the term is used generically in the plural, without caps,
to describe similar  stellar systems.
Globular Cluster a compact spherical cluster of predominately older red stars (e.g M13).
kelvin (K) The scientific temperature scale based on absolute zero (-273.16o C).
Light Year a measure of distance equal to the distance light travels in one year or 63,240 A.U.s.
Magellanic Clouds  Our 2 closest neighboring  galaxies, first seen by Magellan in 1519. The larger one
(LMC) is 33,000 light years in diameter and the smaller one (SMC)  is 19,500 light years in diameter.
Magnitude (apparent)  The brightness of a celestial object as observed from earth.  Originally the
brightest stars were 1st magnitude and the faintest to the eye 6th magnitude. This resulted in a
logarithmic ratio in which 5 magnitudes equaled a brightness of 100 fold. To accommodate brighter stars,
it was necessary to invoke zero and negative values.
Messier Objects  originally, a catalog of 103 nebulae, prepared by Charles Messier in 1784.
Meteor  a streak of light seen when small interplanetary particles hit the earth’s atmosphere and burn up.
Meteorite a meteor which is large enough to reach the earth’s surface before burning up.
Milky Way Our Galaxy which is viewed edgewise and is inclined 63o  to the celestial equator.
Nebula Originally referring to any fuzzy celestial  object, it now applies to any cloud of interstellar gas
and dust, either luminous (emission) or dark (absorption).
Occultation the hiding of a celestial object by another of larger apparent diameter (e.g. solar eclipse).
Open Cluster a loose galactic cluster of predominately young stars (e.g. Pleides M45).
Opposition  when a solar system object has a celestial longitude 180o different from that of the sun.
Parsec  the distance at which one A.U. subtends an angle of  1 arc second; 1 parsec = 3.2616 light years.
Perigee the point closest to the earth of an earth orbiting object.
Perihelion the point closest to the sun of a sun orbiting object.
Planisphere  A map of the circumpolar hemispheres with a rotating overlay, showing the skies at any given
time of the year.
Right Ascension  (RA) the angle of a celestial object from the vernal equinox, measured
eastward along the celestial equator. The angle is generally expressed in hours, minutes and seconds.
Solstices  The 2 times during the year when the ecliptic is most distant from the celestial equator; i.e the
summer solstice (June 21) and winter solstice (December 22).
Time, Sidereal  Time based on the rotation time of the earth with respect to the stars.
Time, Solar  Time based on the rotation time of the earth with respect to the sun.
Terminator The boundary line on a planet or satellite between the dark side and the sunlit side.
Universal Time (UT) is basically Greenwich  Mean Time, the local time at Greenwich, England.   For
conversion to Eastern Standard Time add 5 hours (or 4 hours for Daylight time ).
Twilight The time period between  sunrise or sunset and darkness. Civil Twilight is around sunrise or
sunset. Nautical Twilight is when the the horizon is no longer visible. Astronomical Twilight is when 6th
magnitude stars at the zenith are just visible.