Glossary


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Term Definition Picture
Achromatic Refracting Telescope
Instrumentation
Achromatic Refracting Telescope
Adaptive optics
Terminology
Active optics OR Adaptive optics
AIP
Terminology
AIP - Astronomical image processing
Albedo
Terminology
A measure of the proportion of the total solar radiation received by an astronomical body, such as a planet, that is diffusely reflected away from the body. It is a dimensionless quantity typically measured on a scale from 0 (indicating total absorption of all incident radiation, as by a black body) to 1 (indicating total reflection).
Alt-Az (ALT-AZ)
Instrumentation
Alt-Az (ALT-AZ) - Altitude and Azimuth. Usually applied to a type of mount that moves only up/down, and left/right directions
Amateur telescope making
Terminology
Amateur telescope making (or manufacture) or abbreviation for Atmosphere
Analog to digital
Terminology
Analog to digital
Aperture
Terminology
The diameter of a telescope’s main lens or mirror — and the scope’s most important attribute. As a rule of thumb, a telescope’s maximum useful magnification is 50 times its aperture in inches (or twice its aperture in millimeters).
Aphelion
Terminology
The point at which a body orbiting the Earth's Sun is furthest from the Sun. Opposite of perihelion. See perihelion.
Apochromatic
Terminology
APO - Apochromatic - A 2, 3, or 4 element objective lens whose color correcting characteristics meet the criteria to be classified as "APO"
Apparent field of view
Terminology
Apparent field of view is the angular diameter, expressed in degrees (°), of the circle of light that the eye sees through the eyepiece. The angular diameter of this circle is called the apparent field of view (AFOV) and is a fixed property for each eyepiece design.
APSIG
Organization
Astro-Photography Special Interest Group
ASCOM
Terminology
ASCOM - Astronomy Common Object Module (a set of common interface standards for several categories of equipment)
Asterism
Terminology
Any pattern of stars recognizable in Earth's night sky. An asterism may form part of an official constellation or it may be composed of stars from more than one constellation or stars from just a tiny part of a constellation.
Astrometry
Terminology
The branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies.
Astronomical Unit
Terminology
Astronomical Unit (measure of interplanetary distances and represents the mean distance between the Earth and our sun or = 149597871 Km or ≈ 92.955807 million miles)
Astronomy Photo of the Day
Publication
Astronomy Photo of the Day
Astrophotography
Terminology
Astrophotography ALSO Astrophysics
Astrophotography Tool
Software
Astrophotography Tool is software used for image acquisition, telescope control, and many other ancillary duties that aid in image acquisition
ASV
Organization
ASV - Astronomical Society of Victoria
ATMSIG
Organization
ATMSIG - Amateur Telescope Making- Special Interest Group
AVI
Terminology
AVI - Audio video interleaved (a video file format)
Bino Viewer
Instrumentation
Bino Viewer
Black Hole
Celestial Object
Black Hole
Bortle
Terminology
The Bortle sky scale is a nine-level numeric scale that measures the night sky's brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution. John E. Bortle created the scale and published it in the February 2001 edition of Sky & Telescope magazine to help amateur astronomers evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites. The scale ranges from Class 1, the
BRC
Instrumentation
Baker-Ritchey-Chretien
Cartes du Ciel
Software
Cartes du Ciel is a freeware planetarium program. It also provides for telescope mount control through the ASCOM drivers
Cassegrain telescope
Instrumentation
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes. The main characteristic being that the optical path folds back onto itself, relative to the optical system's primary mirror entrance aperture. This design puts the focal point at a convenient location behind the primary mirror and the convex secondary adds a telephoto effect creating a much longer focal length in a mechanically short system. Display
Catadioptric
Terminology
A catadioptric optical system is one where refraction and reflection are combined in an optical system, usually via lenses (dioptrics) and curved mirrors (catoptrics).
Center of gravity
Terminology.
Center of gravity
Charge coupled device
Terminology.
Charge coupled device sensor is the basis for the more expensive astro cameras on the market due to the high quantum efficiencies of that sensor.
Chromatic aberration
Terminology.
Chromatic aberration is when visible light passes through a glass lens it gets dispersed, or split, into its many colors. A lens focuses each color at a different point, causing a fringe of color to appear around bright objects.
Coma
Terminology
Aberration inherent to certain optical designs (most commonly the Newtonian reflector telescope) that results in off-axis point sources such as stars appearing distorted, appearing to have a tail (coma) like a comet.
Complimentary Metal Oxide Semiconductor
Terminology
Complimentary metal oxide semiconductor sensor is a less expensive sensor alternative for astrophotography cameras.
Computerized German Equatorial Mount
Instrumentation
A computerized mount that when polar aligned can be used with the Declination and Right Ascension coordinate system.
Coordinated Universal Time
Terminology
is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time at 0° longitude, and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT).
Coronal mass ejection
Terminology
Coronal mass ejection is a significant release of plasma and accompanying magnetic field from the solar corona. They often follow solar flares and are normally present during a solar prominence eruption.
Dall-Kirkham
Instrumentation
A telescope design that uses a concave elliptical primary mirror and a convex spherical secondary. While this system is easier to grind than a classic Cassegrain or Ritchey–Chrétien system, it does not correct for off-axis coma. Field curvature is actually less than a classical Cassegrain. Because this is less noticeable at longer focal ratios, Dall–Kirkhams are seldom faster than f/15.
Declination
Terminology
In the equatorial coordinate system, declination is the celestial equivalent of terrestrial latitude. Coordinates north of the celestial equator are measured in positive degrees from 0° to 90°, while coordinates to the south use coordinates in negative degrees.
Deep Sky Stacker
Software
Deep Sky Stacker is freeware for astrophotographers that simplifies all the pre-processing steps of deep sky pictures. Registering, stacking, and simple post-stacking processes to quickly view the final result.
Deep-Sky Object
Terminology
A deep-sky object (DSO) is any astronomical object that is not an individual star or Solar System object (such as Sun, Moon, planet, comet, etc.). The classification is used for the most part by amateur astronomers to denote visually observed faint naked eye and telescopic objects such as star clusters, nebulae and galaxies.
Digital Single Lens Reflex camera
Instrumentation
Digital Single Lens Reflex camera is a digital camera that combines the optics and the mechanisms of a single-lens reflex camera with a digital imaging sensor.
Dobsonian
Instrumentation
A Dobsonian telescope is an alt-az mounted Newtonian telescope design popularized by John Dobson in 1965 and credited with vastly increasing the size of telescopes available to amateur astronomers. Display
Electronic Auto-Focuser
Instrumentation
Electronic Auto-Focuser
Electronically Assisted Astronomy
Terminology
Electronically Assisted Astronomy
Equatorial
Terminology
Usually applied to any mount that can be Polar or Equatorially aligned
Explore Scientific
Company/Vendor
Explore Scientific uses Jinghua Optical Corporation (JOC) as the exclusive manufacturer of Explore Scientific products, while being the exclusive distributor of Bresser products throughout the Americas.
Eyepiece
Terminology
Eyepiece - is a type of lens with a specific design characteristic (eg. Ramsden, Plossl, Orthoscopic, etc) that is attached to a variety of optical devices such as telescopes
Field Flattener
Instrumentation
Field Flattener - Corrects Field Curvature. Most telescopes have pronounced 'field curvature', it means that the focus plane is curved like a fishbowl. When the focus plane is curved and the sensor is flat, there is no focus position where the image will be in focus from the center all the way to the edges.
Field of View
Terminology
Sometimes used interchangeably with True Field of View (TFOV). It is how much sky you can see through the eyepiece, measured in degrees.
Focal Length
Terminology
Focal Length of an objective lens or mirror, usually measured in millimeters
Focal Ratio
Terminology
Focal Ratio - found by dividing the focal length by the aperture. The smaller the f/number, the lower the magnification, the wider the field, and the brighter the image with any given eyepiece or camera.
Focal Reducer
Instrumentation
Focal Reducer - a set of converging (or positive) lenses that cause the light from a telescope objective to converge at a steeper angle to the focal plane as if it were coming from an objective with a faster (lower) focal ratio and a shorter focal length.
Full Width Half Maximum
Terminology
Full Width Half Maximum indicates the width of the star profile half way to the peak. That is a standard measure of the size of a star on your imaging sensor, and should be constant regardless of star intensity - and that's why it's a good measure of sharpness and focus/seeing/guiding quality.
Gamma Ray Burst
Terminology
Gamma Ray Burst - A cataclysmic event that generates a brief but intense outburst of gamma ray radiation which can be detected from billions of light-years away. The source of most GRBs is theorized to be supernova or hypernova explosions of high-mass stars. Short GRBs may also result from the collision of neutron stars.
German Equatorial Mount
Instrumentation
A mount that when polar aligned can be used with the Declination and Right Ascension coordinate system.
Globular Cluster
Celestial Object
Globular Cluster - a spherical collection of stars that orbits a galactic core. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes, and relatively high stellar densities toward their centers.
GNU image manipulation program
Software
GNU image manipulation program (GIMP) is a cross-platform image editor
GoTo
Terminology
Computerized telescope mount that allows selecting an object and having the mount move the telescope to the selected position.
Great Red Spot
Celestial Object
Jupiter's Great Red Spot
Guan Seng Optical
Company/Vendor
Guan Seng Optical specializes in Ritchey-Chretiens and imaging Newtonians plus many other "Astro" products
Hand Controller
Instrumentation
A Hand Controller or Hand Box (HBX) is used to control the functions of a motorized telescope mount, either Alt-Az or CGEM
Hertzsprung–Russell
Terminology
Hertzsprung–Russell diagram - A plot of luminosity versus effective temperature for a population of stars; depending on the usage, the star's absolute magnitude may be substituted for luminosity, and its color index or spectral type for temperature. Display
Hubble Space Telescope
Space Telescope
The Hubble Space Telescope is a space telescope that was launched into low Earth orbit in 1990 and remains in operation today. Display
Hydrogen alpha
Terminology
Hydrogen alpha - is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28 nm
Index Catalog
Catalog
Index Catalog - The first major update to the NGC of Nebulae and Clusters of Stars, published in two parts by Dreyer in 1895 (IC I,[5] containing 1,520 objects) and 1908 (IC II,[6] containing 3,866 objects). It serves as a supplement to the NGC, and contains an additional 5,386 objects
International Astronomical Union
Organization
International Astronomical Union is an international association of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy
International Space Station
Spacecraft
The International Space Station is a modular space station in low Earth orbit. The ISS programme is a multi-national collaborative project between five participating space agencies: NASA, Roscosmos, JAXA, ESA, and CSA.
Jones-Bird
Instrumentation
A Jones-Bird reflector telescope (sometimes called a Bird-Jones) is a mirror-lens (catadioptric) variation on the traditional Newtonian design. The design uses a spherical primary mirror in place of a parabolic one, with spherical aberrations corrected by sub-aperture corrector lens usually mounted inside the focuser tube. Display
Large Magellanic Cloud
Celestial Object
The Large Magellanic Cloud is a satellite galaxy of the Milky Way. At a distance of about 50 kiloparsecs, the LMC is the second- or third-closest galaxy to the Milky Way and is located in the constellation Dorado
Light Pollution
Terminology
That nasty pernicious man-made glow that infects our night skies and denies us the extreme pleasure experienced when enveloped in a truly dark sky setting
Mak-Newt
Instrumentation
Mak-Newts are a telescope design that uses a lens and mirrors. The mirrors are configured like standard a Newtonian, except a standard Newtonian has a parabolic primary mirror, Mak-Newts use a spherical primary mirror. So Mak-Newts have a meniscus-shaped lens at the front end of the optical tube that eliminates spherical aberration. Mak-Newts have one-fourth the coma of a standard Newtonian but they do suffer from mild field curvature. Finally, the secondary mirror in the Mak-Newt is attached to the correc
Meridian
Terminology
A line running north–south across the sky and passing through the point directly overhead known as the zenith.
Messier Object
Catalog
Messier Objects - One of a set of 110 "nebulous" astronomical objects, of which 103 were cataloged by French comet hunter Charles Messier between 1771 and 1781.
New General Catalog
Catalog
New General Catalog - a catalog of deep-sky objects compiled by John Louis Emil Dreyer in 1888. It expands upon the cataloging work of William and Caroline Herschel, and John Herschel's General Catalog of Nebulae and Clusters of Stars. The NGC contains 7,840 objects, known as the NGC objects.
North Celestial Pole
Terminology
The north celestial pole is the imaginary points in the sky where the Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. It is the point around which the heavens seem to turn.
Off-Axis Guider
Instrumentation
An off-axis guider sends starlight to your guide camera by using an internal pick-off prism that redirects light coming from the edge of the telescope's circular field of view.
One-Shot Color
Instrumentation
A type of Astro camera that captures color images as opposed to monochrome (mono) images.
Open Cluster
Celestial Object
Open Cluster - a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist.
Optical Tube Assembly
Instrumentation
Optical tube assembly is the cylinder that houses all the optics of your telescope.
Perihelion
Terminology
The point at which a body orbiting our Sun is closest to the Sun. Comes from peri = near and helion = our Sun Display
Periodic Error Correction
Terminology
Periodic error is the name for the inevitable small mechanical errors that occur in the drive gearing as the scope is tracking during long-exposure imaging. Since these errors are part of the scope’s drive and are predictable, they can be evaluated and counteracted to improve tracking for astro-imaging.
Planetary Nebula
Celestial Object
Planetary Nebula - is a type of emission nebula consisting of an expanding, glowing shell of ionized gas ejected from red giant stars late in their lives. The term "planetary nebula" is a misnomer because they are unrelated to planets or exoplanets. The term originates from the planet-like round shape of these nebulae observed by astronomers through early telescopes. Display
Quantum Efficiency
Terminology
It is the incident photon to converted electron ratio of a photosensitive device. Or simply, the ratio of how many photons that strike your sensor that actually get turned into electrons.
Red Dot Finder
Instrumentation
The red dot finder is a form of reflex finder and as such does not suffer from parallax. This non-magnifying sight uses a type of beam splitter to "reflect" a dot generated by collimating optics into the users field of view.
Right angle correct image
Terminology.
Right angle correct image, the term is usually applied to finder scopes.or a diagonal.
Right Ascension
Terminology
Right Ascension - In the equatorial coordinate system, the celestial equivalent of terrestrial longitude. It divides the celestial equator into 24 hours, each of 60 minutes.
Ritchey-Chrétien
Instrumentation
Ritchey-Chrétien telescope is a specialized variant of the Cassegrain telescope that has a hyperbolic primary mirror and a hyperbolic secondary mirror designed to eliminate off-axis optical errors (coma). The RC has a wider field of view free of optical errors compared to a more traditional reflecting telescope configuration. Display
Schmidt–Cassegrain
Instrumentation
Schmidt–Cassegrain is a catadioptric telescope that combines a Cassegrain reflector's optical path with a Schmidt corrector plate in front of the secondary mirror to make a compact astronomical instrument that uses simple spherical surfaces. Display
Sky Quality Meter
Instrumentation
Measures the brightness of the night sky in magnitudes per square arc second.
SkyWatcher
Company/Vendor
David Shen founder of Synta Optical is the company that produces the Sky-Watcher brand.
Small Magellanic Cloud
Celestial Object
The Small Magellanic Cloud is a dwarf galaxy near the Milky Way located in the constellation Tucana
South Celestial Pole
Terminology
The south celestial pole is the imaginary points in the sky where the Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. It is the point around which the heavens seem to turn.
StarTools
Advanced Image Processing Software for Astrophotography StarTools is a powerful new type of image processing engine. It tracks your signal and its noise component as you process. The result is less noise, more detail, ease of use, and unique advanced post-processing power compared to any other software.
External link: StarTools Link
StellarVue
Company/Vendor
Stellarvue is the telescope division of Auburn Precision Optics located outside of Sacramento, California. They produce Apochromatic Triplet telescope and other "Astro" gear.
Supermassive Black Hole
Celestial Object
Supermassive Black Hole - is the largest type of black hole, containing a mass of the order of hundreds of thousands to billions of times the mass of the Sun.
Telrad
Instrumentation
Telrad finder consist of a small ground glass screen onto which is projected a circular reticle from a red LED that shows a fixed angular diameter projected onto the sky. The image of the projected reticle is nearly free of parallax, which means the reticle appears in a fixed position against the distant sky no matter where you place your eye behind the finder.
The Sky Searchers
Terminology
Abbreviation for The Sky Searchers. This is the forum you are on.
TSS Picture of the Day
Terminology
TSS Picture of the Day

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