May 05

Glossary Of Telescopes

Here’s a glossary for the different bits of terminology which are all part of the fascinating hobby of astronomy.

Glossary Of Telescopes

Absolute Magnitude

The measurement of just how bright a star actually is

Accessory Tray

A small metal tray attached to the telescope mount or tripod using for storing eyepieces, lenses, etc


The size of the primary mirror or lens, so an 8-inch telescope has an 8-inch aperture, generally speaking

Altazimuth Mount

A mount very similar used to that in photography – it rotates on 2 axes


Refracting telescopes suffer from an issue called chromatic aberration and this specialized type of lens corrects this problem

Balance System

For larger and heavier telescopes a set of counterweights are used to balance everything out

Barlow Lens

This type of lens, named after Peter Barlow, can increase the focal ratio of a telescope by 200% – 300%

Blower Bulb

Also called an air bulb, these are used to gently blow dirt or dust from a telescope lens or other surface, helping you avoid getting fingerprints on the lens


This is a type of telescope which uses both lenses and curved mirrors to form images in the focusing system.


When a reflecting telescope requires the adjustment of its primary and secondary mirrors this process is known as collimation

Collimation Cap

A cap specially designed to help with the calibration/collimation of a reflector telescope


These can also be dots, rings or crossed wires used in a finder scope or eyepiece to help center what you’re looking at

Dew Shield

This is a metal shield which is placed around the optical tube to prevent dew forming on the lens


This is a special type of telescope mount which is like a combination of a Lazy Susan and a teeter-totter

Electronic Drive

Used on computerized and manual telescopes to help with the tracking of deep-sky objects

Equatorial Mount

This type of mount is very popular on large refracting and reflecting telescopes because it allows precise manual tracking of moons, planets, stars etc


Plossl and Kellner are the most common types and this component is what focuses all that light into the image you finally get to wonder at

Field of View

The “amount” of sky you can see by looking through any single eyepiece – measured in degrees

Finder Scope

A small secondary telescope used to help you align your telescope with whatever celestial object you want to look at


A collection of billions of stars which are very close together – our Milky Way is an example of a galaxy


Light Emitting Diode – these are used in all types of electronic and portable computer displays

Light Grasp

This is the amount of light any lens or mirror can gather, and generally speaking the wider the aperture the greater the light grasp

Light Pollution

All of the artificial light created by house and street lights which interfere with the visibility of the night sky


How you measure the brightness of a star or other deep-sky/Messier object.


This is a type of catadioptric/compound telescope

Messier Objects

These are the deep-sky (very distant) objects which were cataloged by Charles Messier in the 18th century.


A nebula is a gigantic cloud of dust, gas and plasma which can be seen from millions of light-years away

Newtonian Reflector

Some people will call reflector telescopes a Newtonian telescope

Optical Tube

This is the main body of the telescope itself, made up of the casing and a primary mirror or lens

Polar Alignment

The process of aligning your telescope with Ursae Minoris, otherwise known as the Pole or North Star

Rack-and-Pinion Focuser

A device used to assist in the focusing of your telescope


A type of telescope which uses one or more mirrors to focus gathered light into an eyepiece


The higher the resolution of your telescope the clearer and more detailed the images will be


This is a type of catadioptric, or compound, telescope

Sidereal Rate

The movement of the stars across the sky as our planet rotates in relation to them


The frame at the front of a reflector telescope which holds the secondary mirror in place


A three-legged mount for a telescope, which can feature either a pan or swivel head

Be Sociable, Share!