As an un-worthy update to the original masterpiece by Joe Cipriano (un-editable and locked in the archives), here is a list of ASTRONOMY-related abbreviations and terms frequently found on Cloudy Nights. Please feel free to add suggestions, which we can roll into the list over time. We do not, however, want to get too specialized - this is the Beginners' Forum after all. This thread will be linked from the pinned "Best of the Beginners' Forum & How-Tos" message. Thanks to all.
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Achro - Achromatic Refractor, or Achromat
AFoV - Apparent Field of View. Refers to the visual size of the field seen through an eyepiece, not the actual angular sky coverage. See also TFoV.
AG - Autoguider
Alt - Altitude
Alt/Az - Altazimuth mount
Apo - Apochromatic Refractor, or Apochromat
ATM - Amateur Telescope Making (or Maker)
Az - Azimuth
CA - Chromatic Aberration, an optical defect causing colors to come to different foci.
Cass - Cassegrain Reflector. See also Mak, RC, SCT.
Cat - Catadioptric Telescope. See also Mak, MN, SCT, SN.
CCD - Charged Coupled Device. A technology used to build sensors in digital cameras.
CF - Carbon Fiber (or Fibre) in reference to OTA material.
CO - Central Obstruction. Typically a secondary mirror in a reflector which blocks a portion of incoming light.
COL - Computerized Object Locator.
CMOS - Complementary Metal–Oxide–Semiconductor. A technology used to build sensors in digital cameras.
CSC - Clear Sky Chart
CW - Counterweight
Dec - Declination
Dob - Dobsonian Telescope
DSC - Digital Setting Circles. Electronically display direction scope is pointed in RA/Dec coordinates.
DSO - Deep Space Object. Refers to most objects outside our solar system, including but not limited to galaxies, planetary nebula, globular clusters, etc.
DT - Dovetail plate
ED (glass) - Extra low Dispersion glass, a type of glass allowing better color correction in a refractor.
EoFB - Edge of Field Brightness
EP - Eyepiece
Eq - Equatorial Mount
FF - Field Flattener
FF/FR - Field Flattener/Focal length Reducer. See also FR.
FL - Focal Length
FOV - Field of View
FR or f/ - Focal Ratio. FR also Focal length Reducer. See also FF/FR.
GEM - German Equatorial Mount. See also EQ
HC - Hand Controller
JD - John Dobson. Inventor of the Dobsonian. See also Dob.
LP - Light Pollution
LPZ - Light Polluition Zone, a descriptor of light pollution found in the area.
Mak - Maksutov-Cassegrain Telescope
MN - Maksutov-Newtonian Telescope
MOT - Mirror On Top. ATM term for mirror grinding, where the mirror is on top of the grinding tool. See also TOT.
NEAF - NorthEast Astronomy Forum & Telescope Show.
NEAF Blem - New but blemished equipment sold by manufacturers at NEAF, having flaws that do not impact functionality. See also NEAF.
NELM - Naked Eye Limiting Magnitude
Newt - Newtonian Reflector
OAG - Off-axis Guider
OTA - Optical Tube Assembly
PE - Periodic Error. Tracking errors caused by the imperfections inherent in any worm gear system. These errors repeat every rotation of the worm, hence Periodic.
PEC - Periodic Error Control or Correction. A method of sending pre-recorded corrections to compensate for mount periodic error.
PPEC - Permanent Periodic Error Correction. A version of PEC whereby the recorded corrections are retained in the mount after power loss.
RA - Right Ascension
RACI - Right-Angle Correct-Image finder - flips image to correspond to what the eye sees unaided.
RC - Ritchey-Chretien Telescope
RDF - Red Dot Finder [Form of Unity or Unit-power (1x magnification) finder]
ROR - Roll Off Roof, a type of observatory design
RFT - Rich Field Telescope
SA - Spherical Aberration, An optical defect
Sb - Surface brightness (or a Barred Spiral galaxy, depending on context)
SBS - Side-by-side saddle plate
SCT - Schmidt-Cassegrain Telescope
SD (Glass) - A marketing term for Super Low Dispersion glass, a type of ED glass
SN - Schmidt-Newtonian Telescope
SRF - Slobbering Refractor Freak
Stack - An image created from several frames (sub-exposures), which have been aligned with image processing software.
Sub - Sub-exposure. See also Stack.
TFoV - True Field of View. The actual angular measurement of sky seen through an eyepiece. See also AFoV.
TOT - Tool On Top. ATM term for mirror grinding, where the grinding tool is on top of the mirror. See also MOT.
UTA - Upper Tube Assembly; seldom-used acronym for the secondary cage of a Dobsonian telescope. See also Dob.
Manufacturers/Vendors:
AM or AMart - AstroMart
AP - Astro-Physics (or Astrophotography, depending on context)
BO/TMB or TMB/BO - Burgess Optical/Thomas M. Back
C - Celestron
CN - Cloudy Nights
ES - Explore Scientific
GSO - Guan Sheng Optical
IP - ImagesPlus
MI - Mountain Instruments
MSS - Mercury Systems Support
OGS - Optical Guidance Systems
PI - PixInsight
PS - Adobe PhotoShop
PSP - Jasc (Corel) Paint Shop Pro
RCOS - RC Optical Systems
S&T - Sky & Telescope Magazine
SV - Stellarvue
SW - Sky Watcher
Tak - Takahashi
TMB - TMB (Thomas Back) Optical
TV - TeleVue
Number T number - TeleVue eyepiece reference, "T" refers to "Type"; "17T4" refers to a TV Nagler 17mm Type 4
UO - University Optics
WO - William Optics