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Glossary of Astronomy Terms

Astronomy terms and phrases - what do they mean?

1.25 inch focuser
The standard size eyepiece used for most telescopes is 1.25 inch, thereby the focuser used for these eyepieces uses a 1.25 inch eyepieces design size.
2 inch focuser
Eyepieces come in three sizes - 1 inch, 1.25 inch and 2 inch. This is where a telescope is using 2 inch eyepieces and thereby needs a larger barrel design to fit these large (and wide angle) eyepiece units.
2 inch to 1.25 inch adaptor
Where a 1.25 inch eyepiece is used in a 2 inch focuser a fitting is placed inside the focuser to adapt between the 2 inch eyepiece size and a 1.25 inch eyepiece barrel diameter.
Advanced level astronomy
This is where you have an in depth experience in astronomy, plus also in telescopes and also in finding things in the night sky. Advanced astronomy users are a wonderful support for introductory & intermediate users, and again these types of people are found in the Astronomical Society of Melbourne where some of the highest capability advanced and professional capability astronomers are available.
Advanced level reflecting telescope
This is where the performance of a reflecting telescope achieves a level of excellence where the most demanding users achieve performance that meets their exceptional requirements. Only the best commercial reflecting telescopes achieve this capability rating.
Advanced level refracting telescope
This is where the performance of a refracting telescope achieves a level of excellence where the most demanding users achieve performance that meets their exceptional requirements. Only the best commercial refracting telescopes achieve this capability rating.
Altazimuth mount
Mount enabling simple altitude and azimuth operation, very easy to use with easy up/ down and side to side operation
Aluminisation
Where a mirror is coated on its front surface with a layer of deposited aluminium to reflect an image. All reflecting telescopes use this technology.
Antique brass telescope
This is the old design of telescope where the body and componentry are manufactured from high quality brass, enabling a thing of beauty to be available to the eye as well as a practical telescope itslef as well. These units are usually selected as a feature telescope to be set up inside a home or office.
Aperture
Size measured in inches or centimetres of an optical mirror or lens.
Astronomical Society of Melbourne
This Society is the region's friendliest. They will teach you Astronomy from any level of Introductory through Intermediate and all the way to Advanced level. Also the team includes highly experienced specialists in Double Stars, Lunar & Planetary, Deep Space, Astrophotography and also other areas such as Training and Teaching you the use of a telescope and the Night Sky itself. Email us for details via our website.
Astrophotography
This is the use of a camera on the back of the telescope to enable an image to be created of objects in the night sky. Regarded as an advanced level capability, plus also one where the budget is also higher than the usual telescope system.
Beginner level astronomy
This is your first steps in astronomy, where you are learning the night sky and achieving your first images in a telescope system. Enthusiastic new astronomy users quickly pass this stage and move into intermediate level astronomy, all that is required is some decent quality gear (a good telescope is a must) plus some assistance. The Astronomical Society of Melbourne is always a wonderful place to seek assistance & guidance.
Binoculars
Two identical telescopes mounted side by side and aligned to point accurately in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most are sized to be held using both hands, although there are much larger types.
Carl Zeiss
The Grand Masters of astronomy, very sadly no longer in production. Their gear is without peer, and regarded as the best telescopes ever crafted by mankind. These systems have not been stocked in Australia since the 1980's, and are an exclusive capability to Astronomy Alive (due to our global linkages).
Cassegrain telescope
The Frenchman Cassegrain created this telescope design. This is where multiple mirrors are used to create a shorter tube system than the standard Newtonian telescope design. However these systems are more costly and there are only a few designs where these systems performance is regarded as acceptable (such as Maksutov's).
CCD
A Charge Coupled Device - computerised camera - this is what the computer chip is in a digital camera. For astronomy these can get very large and powerful if you wish to go that high in power and budget.
Clave
Up till the 1970's regarded as the premier manufacturer of refractors and eyepieces in the world, today they no longer manufacture. Their products are exceptionally rare to find and again massively valuable. Yet again a unique offerring from Astronomy Alive (again due to our global linkages).
Collimation
The alignment of the telescope's optics, either the alignment of the lens to the eyepiece in a refracting telesocpe, or the alignment of the mirror on a reflecting telescope. Correct collimation is crucial to maximise performance, as incorrect collimation damages the sharpness and brightness of any telescope.
Collimator
The piece of equipment that is used to align the telescopes optics. The collimator is placed in the focuser of the telescope whilst the alignment is performed, an easy task once demonstrated.
Coloured filters
Planetary filters - enabling increased resolution of planetary detail - such as a blue filter for the polar caps on Mars, plus also a range of other colours for the Rings or Saturn & cloud bands on Jupiter as examples.
Compact binoculars
Small pocket sized binoculars (usually folding up) to take up the absolute minimum in space.
Computerised hand controller
Where a computerised control system enhances the performance of a dual axis motoirised Equatorial mount plus enables a programmable control operation to assist with automated "Find It" capability, plus also enables the accuracy required for astrophotography.
Deep Space filter
Enhancement of fine details In Deep Space is only possible using a premium qiuality Deep Space filter scxrewed onto the end of the eyepiece. This unit enhances to blacks - versus - whites thereby enabling difficult objects otherwise unviewable to be viewed and studied in detail.
Diagonal - mirror type
A 90 degree fitting inserted into a refracting telescope's focuser to enable an upright image (however "Wrong Way Around" view). This is selected for ease of use - as a refracting telesocpe without a 90 degree diagonal means you are going to need to perform a few gymnastics to use the system.
Diagonal - prism type
Selected for a Spotting Application as this unit corrects the image to an "Upright and Correct Way Around" image.
Diagonal 45 degree type
Diagonal for a refracting telescope with a 45 degree bend on the end.
Diagonal 90 degree type
Diagonal for a refracting telescope with a 90 degree bend on the end.
Diffraction limited performance
This is the test for a telescopes performance. A telescope that achieves a "Diffraction Limited" capability has a premium performance capability, simple as that. Very few commercial telescopes achieve this goal, and only the best of the best are in this category.
Digital camera adaptor
The connection required to link a Compact Digital camera to a telescope system. The units fits directly onto the telescope's eyepiece, and the camera directly secures onto a foot on the unit, enabling alignment adjustment to be made, aligning the lens of the camera with the path of the light coming through the telescope's eyepiece, a very easy to use system.
Digital camera spotting scope
A digital camera in a spotting scope, complete with a LCD screen to show what is being viewed and filmed. What an innovative idea.
Dobsonian mount
The easiest to use telescope mount for a Newtonian astronomical telescxope system, featuring ultra easy to use operation. Simple side to side plus up/down operation via hand.
Dual axis drive system
Where both Declination plus also Right Ascension are able to be adjusted. Enabling the mount to track the sky is both axes whilst the earth rotates, again compensating - however this time with incraesed accuracy - for the rotation of the earth. Again both manual & motorised versions available.
ED Glass
ED stands for "Extra Dispersion" glass, invented by premium Japanese specialist glass makers this glass enhanced performance of all optical systems via a flatter field, higher light transmission through the glass plus also sharper images, regarded as a breakthrough product.
ED Glass refracting telescope
Enhanced telescope capability via the use of ED "Extra Dispersion' glass in the telescope system's lens, enabling an advanced level astronomy capability to be achieved.
ED Glass spotting scope
Spotting system featuring a Zoom magnification capability, where revolving the eyepiece increases or decreases magnification, however with the addition of Premiu ED "Extra Dispersion" enhanced capability glass for the maximum in performance.
Equatorial mount
Astronomical mount for a telescope enabling manual or motorised operation to compensate for the rotation of the earth.
Equatorial mounted reflecting telescope
Reflecting telescope mounted on an Equatorial mount which has been selected to enable manual dual axis operation - or - motorised dual axis operation - or - even dual axis motorised operation with Computersied "Go to" capability.
Eye relief
A large eye relief is suitable for eyeglass wearers, as their eye is further from the eyepiece due to their use of spectacles. Higher eye relief eyepieces are expensive and most users (even with eyeglasses) use a Super Plossl or Wide Angle eyepiece to achieve the wider view required.
Eyepiece
This is the unit that you look into to view through a telescope. The eyepiece sits in the end of the telescope systems focuser. It enables a magnified image.
F ratio
Measurement of the focal length divided by the lens or mirror diameter - example: 1200mm focal length divided by 200mm lens/ mirror size = 1200/ 200 = f6
Filter
A filter enhances the performance of the telescope on - Lunar (neutral density type filter), Planetary (such as a blue filter for the polar caps on Mars), plus also a range of other colours for the Rings or Saturn & cloud bands on Jupiter as examples.
Finderscope
This is the small telescope on the side of a telescope that has a smaller magnification, and is used to align the main telescope with objects either for terrestrial spotting use or for astronomy - for astronomy these are a MUST.
Finderscope bracket
The bracket holding the finderscope attaching it to the telescopes tube assembly.
Finderscope Right angle type
This is where the end of the finderscope includes a 90 degree diagonal, enabling an increase in ease of use for the finderscope.
Finderscope straight through type
A straight through style of finderscope - where the finderscope is parrellel to the main telescope tube.
Fluorite glass
What ED "Extra Disperion" glass achieves is even further enhanced by the world's ultra premium substrate for refracting telescopes in Fluorite glass. Fluorite enables ultra premium capability to be available to the telescope system, and is used only on the best telescopes available commercially. It also achieves what is called an Apochromatic" capability to be available to a refracting telesope, where any false colur in the telescopes performance is reduced to either negligible levels or comptletely eradicated all together.
Focal length
Distance measured in millimetres from the center of the lens or mirror to the Focal Point - the point at which the light is concenrated to a single point
Focuser
This is the unit in which the eyepiece is inserted to bring the telescope to a focus and enable to resolution and magnification to be achieved. Popular designs are Rack & Pinion and also the ultra smooth Crayford type.
Go To Control system
Dual axis motorised system where a computerised control system tracks the sky compensating for the earth's rotation, however with the addition of a database (usually 13,436 objects) and automated accurate drive control to enable the accuracy in alignment required for astrophotography.
Hand controller
This unit has either four buttons for advancing and retarding the motos on both Declination & Right Adcension, or a multiple button hand controller where a "Go To" is being utilised.
Intermediate level astronomy
This is where you have experience in the use of a telescope, and understand it's operation, plus also have a some experience finding things in the night sky. Most amateur astronomy enthusiasts are at this level, and are quite happy to stay in this most enjoyable phase of astronomy.
Intermediate refracting telescope
Increased cost over introductory level gear, however with the addition of a massively enhanced number of objects being available for viewing through the telescope system.
Introductory reflecting telescope
Low cost system for the introductory stage of astronomy only, enabling you to achieve a lot with a modest budget.
Introductory refracting telescope
Low cost system for the introductory stage of astronomy or spotting, enabling you to achieve a lot with a modest budget.
Large aperture binoculars
High power binoculars where the larger lens system enables highest possible performance - usually used for bay views, spotting and astronomy.
Low profile focuser
This is where a focuser has a deliberately designed lowered height enabling the design of the telescope tube system to be enhanced for optical use.
Lunar filter
Neutral density or Green filter screwing to the end of the eyepiece to enhance contrast on lunar features.
Magnesium fluoride lens coating
The coating on a refracting telescope, binoculars and eyepieces. This process achieves two goals, firstly protecting the lens from dust and damage, plus secondly protecting the lens from internal reflections
Magnifier
A simple hand held magnification lens to enable objects to be increased in size (such as stamps).
Maksutov Cassegrain reflecting telescope
This is where the short tube design reflecting telescope has been selected for a smaller length tube and easier use for handling to your viewing location.
Microscope
Single or dual eyepiece design to enable close up magnification and viewing of tiny objects, as we call it a "microscopic" view.
Nebula filter
The nebula filter is a specility filter that blocks the gases that we do NOT want such as Sodium, Neon & Argon, whilst letting through the gases that we DO want - ie: Hydrogen. A premium quality Nebula filter is the only way to see real detail in the gas clouds of a nebula.
Newtonian telescope
Sir Isaac Newton invented the Newtonian telescope many centuries ago and it is still the most popular telescope for astronomy due to it's power and cost efficiency. The vast majority of telescopes in all Astronomical Societies are Newtonians due to the ease of use and power at a modest cost.
Opera glass
Low magnification small aperture (to 25mm) binocular system to enhance close up viewing of opera, concerts, stage plays & theatre.
Optical tube assembly
The is the telescope's actual optical system, the tube in which the opticcs are placed which does all the optical work in a telescope, commonly designated as "OTA".
Plossl eyepiece
The world's most popular eyepiece is called a Plossl, invented by a German, this design is the classical two pairs of matched lens elements correcting each others vision and field of view in the eyepiece. This is also the most popular eyepiece commercially globally as its performance is excellent when considering its modest cost.
Quantum
The rarest telescope ever made, these exeptional telescopes were crafted in the US in the late 1970's and early 1980's. They are massivly sought after and exceptionally prized, they are also a unique offerring from Astronomy Alive (again due to our global linkages).
Questar
Competitor to Quantum, and still available today. These are an exceptional capability systems, also exceptionally prized and regarded, but are very expensive.
Red light torch
Nearly all Astronomical Scoieties have significant restrictions on white lights at their viewing events. This is because white light damages "Dark Sky Adaptation", and thereby reduces the performance of the viewing experience. The Red Light Torch enables this Dark Sky Adaptation to be maintained whilst you view through your eyepiece set or star chart, enabling your viewing experience to be significantly enhanced.
Reference Grade performance
This performance level is the standard for professional observatories and professional level astronomy enthusiasts gear. Reference Grade gear is even rarer than Diffraction Limited capability, and only very few telescopes achieve this standard globally.
Reflecting telescope
The mirror telescope, where the image is created using a series of mirrors to reflect the image from one mirror to another and concentrate the power of the optical system to and including the focuser and its eyepiece.
Refracting telescope
The classical "Captain Cook" type telescope, where the lens is in the front and the eyepiece at the rear, also regarded as the purists telescope as premium refractors are highly prized.
Saxon
Excellent quality manufacturer of the most comprehensive range of optical system and accessories in Australia, with a 100% manufacturers warranty support and also a dedicated Australian service centre in Melbourne.
Silicone dioxide overcoating
Where a layer of Silicone Dioxide is over coeated over the top of the aluminium on a telescope mirror, thus maximising longevity of the optical surface and also protecting it against dust and damage.
Single axis drive system
Where one axis (Declination) only is motorised, enabling the mount to track the sky whilst the earth rotates, compensating for the rotation of the earth.
Single Optic aluminisation
This is where a mirror is coated where ONE only optic is placed in the Epicentre of the aluminisation chamber only. This enables the mirror to have a perfectly even and unblemished coating on its surface, plus the performance of the telescope to be maximised to its ultimate capability.
Skyscan controller
This is the Saxon & Skywatcher control system for their Go To telescope mounts, again a highly easy to use system with exceptional power and capability.
Skywatcher
Excellent quality manufacturer of the most comprehensive range of optical system and accessories in Australia, with a 100% manufacturers warranty support and also a dedicated Australian service centre in Sydney.
Slow motion controls
Used to slow the telescope from side to side and up and down to line up with different targets, both manual and motorised versions available on the market.
SLR camera adaptor
Enables direct connection of a SLR camera to a telescope's focuser, most units include the capability to mount internally within the adaptor an eyepiece to perform that is known as "eyepiece projection" photography (higher magnification capability).
Solar filter
The ONLY way to view the Sun safely is whith a FULL APERTURE Solar filter. This blocks the vast proportion of the sun's rays BEFORE they even get to the telescopes optics, thereby enabling surface details such as Sun Spots to be viewed easily, and affordably.
Spotting scope
Small telescope system specifically designed for terrestrial viewing - ie: Viewing ships on the bay, Mountains in the distance and Kangaroos in the field.
Spotting scope including mount & tripod
A "total system" capability where the spotting scope is mounted on a dedicated tripod and mount system with slow motion controls to adjust the systems movement to obejcts being viewed.
Standard binoculars
The traditional size and style binoculars, enhancing power and performance.
Starbook controller
This is Vixen of Japan's "Go To" control system, regarded as the highest ease of use Go To control system available commercially globally.
Super Plossl eyepiece
This is an advancement on the Plossl design, where usually an additional lens element us added to enable an further increase in performance, many of the world's best eyepieces are Super Plossl's and they are enormously popular.
Takahashi
The Japanese masters of astronomy, globally regarded as one of the best brands in the world.
TEC
This US based manufacturer is a leader is refractors and Maksitov Cassegrains, their quality and performance are at the highest level of capability available globally, and represent exceptional quality.
Telescope
Instrument for concentrating light to magnify an object for close up viewing with increased resolution on a distant object.
TeleVue Genesis
The Genesis was the world's pioneer in fluorite optics, and is a classic. Whilst TeleVue have gone on to design and market a successful eyepiece selection, the Genesis stands alone as the pinnacle of their capability. Exceptionally rare to find them in such great condition. Yet again a unique offerring from Astronomy Alive (again due to our global linkages).
TMB
Thomas Back tragically passed away in September 2007. His business produced some of the highest capability refracting telescopes and exceptional German glass and design eyepieces (based off the Carl Zeiss designs). This gear is only available 2nd hand now, other than a few last pieces left over from when they were marketed as new, exceptional capability and massively valued, and increasing in value all the time. Yet again a unique offerring from Astronomy Alive (again due to our global linkages).
Truss Tube Dobsonian mount
Longer Newtonian telescopes are too large to be transported and easily hand carried, they are thereby assembled using extension poles to enable a large and high power system to be transportable.
Ultra High Contrast filter
Enhancement of the contrast between difficult objects is only available via the use of a Contrast Enhancement filter. Thus enables difficult objects otherwise unviewable to readily be viewed in detail with a telescope.
Ultra wide angle eyepiece
This is where the eyepiece has an even wider field of view - usually 82 degrees. This is also a higher cost eyepiece, and is again very sought after. This selection needs to carefully considered as the performance of some ultra wide angle eyepieces does not match the cost of the eyepieces themselves. The most popular Ultra Wide's are by William Optics due to the lower than usual cost whilst maintaining a very high performance capability.
Unitron
The 1960's to 1980's featured one major Japanese manufacturer that dominated th e global scene, Unitrom. Using premium Japanese components and technology they produced some of the highest regarded refractors in the world at the time, and still massively sought after and regarded today. Yet again a unique offerring from Astronomy Alive (again due to our global linkages).
Vixen
Famous Japanese manufacturer of a wide range of speciality refracting and Cassegrain telescope for intermediate and advanced level astronomy use. Plus a selection of the highest performing Equatorial mount for advanced level astrophtoography (featuring the exceptional Starbook Go To computerised contol system).
Wide Angle eyepiece
The field of view in a Wide Angle eyepiece is greater than a standard Plossl or Super Plossl, the Plossl design is usually arounf the 50 degree field of view, and the Super Plossl is usually around 53 degrees. The Wide Angle is usually in the range of 67 to 72 degrees, enabling an increased field of view whilst maintaining the magnification of the system, an excellent idea and very highly sought after by those more experienced in astronomy.
William Optics
Global leading technology in refracting telescopes and premium quality eyepieces, specialising in Wide Angle (Swan series 72 degree) and Ultra Wide Angle (82 degree Uwan series) eyepieces. Outstanding value for money using lower cost strategy than competing brands, thereby enabling a premium capability at a lower price, highly recommended.
Zoom binoculars
Featuring a zoom magnification capability where the image is able to be increased in size via a simple lever on the side of the binoculars being pushed.
Zoom eyepiece
Suitable for spotting (terrestrial) viewing, but not recommended for astronomy. The Zoom eyepiece rotates enabling an increased magnification to be available to the viewer whilst not having to change the eyepiece in the telescope's focuser.
Zoom spotting scope
Spotting system featuring a Zoom magnification capability, where revolving the eyepiece increases or decreases magnification.