DEFINITION OF TERMS GLOSSARY I-L Telescopes, Binoculars, Spotting Scopes, Microscopes, Riflescopes, Astronomical Accessories,Refractor,Reflector,Monoculars,Night Vision,Cassegrain,GPS,Optical Tubes,Digital Camera,Eyepiece,Filters,Barlow,Lenses,Diagonals,Prisms,Tripods,Mounts,Finder Scopes,BinoViewers,Optics,Astronomy,Astrophotography,Laser Range Finders,Rangefinders, Top Rated
Secure website, verified, safe for online shopping
The World's Largest Selection of Optics for Astronomy, Sport, Science and Education
Shop By Price
Shop By Interests
Gift Certificate

 


DEFINITION OF TERMS (GLOSSARY): I - L

  Scope City's Optics Crash Course
Tell Friend  

I

Ice A term used to describe water or a number of gases such as methane or ammonia when in a solid state.

Inclination A measure of the tilt of a planet's orbital plane in relation to that of the Earth's.

Index of Refraction The light-bending power of a transparent substrate.

Inferior Conjunction A conjunction of an inferior planet that occurs when the planet is lined up directly between the Earth and the Sun.

Image Processing - the processing of a digital image to eliminate noise, improve contrast, sharpen focus, and rectify color errors.

Inferior Planet A planet that orbits between the Earth and the Sun. Mercury and Venus are the only two inferior planets in our solar system.

Infrared filter - a filter designed to prevent the entry of infrared light into a digital camera. This is because such frequencies of light can overload the chip and cause reduced contrast and sensitivity.

Integrated Barlow - a reference to a design method that allows an eyepiece of short focal length to be made by using a longer focal length eyepiece with a permanent Barlow built into the eyepiece below the field stop, to bring the effective focal length back down. This is usually done to allow the manufacture of short focal length eyepieces with good eye relief. In almost all cases, the term is incorrect, since true Barlows are not used for this purpose. Instead, it behooves the designer to optimize both the negative elements and the rest of the eyepiece, creating a system in which neither the "Barlow" nor the rest of the ocular will work properly on their own. Also referred to as a Smyth lens.

Interference The process in which light waves reinforce or cancel each other.

Interstellar Medium The gas and dust that exists in open space between the stars.

Irregular Galaxy A galaxy with no spiral structure and no symmetric shape. Irregular galaxies are usually filamentary or very clumpy in shape.

Isobar - on a weather map, this is a line of equal pressure.

Isophote - in a visual image, this is a line of equal brightness. If the telescope can only reach a certain faintness of magnitude, the edge of the visible image will represent the faintest isophote visible.

J

John Dobson. Inventor of the Dobsonian. See also Dob.

K

Kellner - An economy eyepiece employing a cemented doublet lens and singlet lens: invented in 1849. This eyepiece is orthoscopic in its traditional configuration. Has about 0.5x its focal length in eye relief.
Two variations of it exist. One of them, the Pl?ssl, is a superb eyepiece.

Kellner, Carl: founder of the optics firm Optical Institute (Wetzlar, Germany) in 1849, which later became E. Leitz, Inc., Kellner was born March 26, 1826 in Wetzlar. Worked for Repsold prior to founding his own firm. Kellner designed the Kellner eyepiece for telescopic use in 1849. The eyepiece was later included on microscopes sold by his company. Kellner died of tuberculosis at age 29, in 1855.

Kidney bean: a blacking out of parts of the field of view, caused by spherical aberration of the exit pupil. Rays with large exit angles intersect the optical axis nearer to the eye lens than those rays with small or moderate exit angle. This results in the kidney bean effect when the circle of least confusion of the exit pupil of the eyepiece exceeds the size of the observer's eye pupil - in other words, when the observer's eye gets too close to the eye lens. The effect is therefore more pronounced with a smaller pupil; i.e., kidney bean is more evident in daytime than during night. True kidney-beaning is not sensitive to what telescope is in use; it is the same for a given eyepiece no matter what telescope is used. This term is often, mistakenly, used to describe the ˇ°black-outsˇ± that naturally occur when the eye is positioned too close to the eyepiece and the pupil doesn't field the whole image from the eyepiece.

Konig: denotes one of a class of eyepieces by a prolific designer, or eyepieces adapted from those designs. The 1:1:2, 1:2:1, 2:1:1, and 1:2:3 configurations are most common. Some people think the 2:1:1 type is properly called a Bert¨¨le. One of the original K?nig designs is a simplification of the Erfle and has a two element field group and a single element eye lens; the field group is quite thick in this design and this eyepiece is not the same as the superficially similar RKE. Most of the popular K?nigs are of the 1:2:1 configuration.

Konig, Albert: optical designer, born 16th August 1871 in Plettenberg. His doctoral thesis in 1894 was on Fresnel diffraction spectra, and was supervised by Ernst Abbe. The same year he began work at Carl Zeiss Inc., working on telescopes, distance measuring equipment, and various other instruments. He died 30 April 1946 in Jena.

Kelvin A temperature scale used in sciences such as astronomy to measure extremely cold temperatures. The Kelvin temperature scale is just like the Celsius scale except that the freezing point of water, zero degrees Celsius, is equal to 273 degrees Kelvin. Absolute zero, the coldest known temperature, is reached at 0 degrees Kelvin or -273.16 degrees Celsius.

Kepler's First Law A planet orbits the Sun in an ellipse with the Sun at one focus.

Kepler's Second Law A ray directed from the Sun to a planet sweeps out equal areas in equal times.

Kepler's Third Law The square of the period of a planet's orbit is proportional to the cube of that planet's semi major axis; the constant of proportionality is the same for all planets.

Kuiper Belt A large ring of icy, primitive objects beyond the orbit of Neptune. Kuiper Belt objects are believed to be remnants of the original material that formed the solar system. Some astronomers believe Pluto and Charon, and now Eris, Sedna, Quaoar, and others are Kuiper Belt objects.

L

Lanthanum: a type of exotic glass developed using a tiny mixture of lanthanum, a silvery metallic element which is one of the rare-earth metals, in the glass. Lanthanum oxide added to glass gives it a higher refractive index and Abbe value than crown or flint. This difference can be exploited by a good designer to reduce aberrations in lens systems. The term lanthanum derives from a Greek word meaning roughly "to lie hidden." Note: this refers to lanthanum glass - lanthanum is opaque.

Laser Collimator - a collimation tool that uses the straightness of a laser beam to collimate the optical elements. This type of device is prone to miscollimation itself, so it should never be used as the ONLY collimation tool.

Lateral Color Chromatic aberration occurring increasingly from the center of the field. Also called Transverse Chromatic Aberration: caused by the off-axis imaging characteristics of a lens being wavelength dependent, i.e., lateral color is off-axis chromatic aberration. It results in a star imaged at the edge of the field being smeared out into a rainbow or showing color fringing.

LED - Light Emitting Diode. This is a small, intensely bright, emitter of light that can take the place of incandescent bulbs for field use at the telescope. They are more energy efficient and last far longer. In addition, LEDs that emit light only in the deep red can be used, which has less of a negative impact on night vision than a white light with a red filter.

Lenticular Galaxy A lens-shaped galaxy that contains no conspicuous structure within the disk. Lenticular galaxies tend to look more like elliptical galaxies than spiral galaxies.

Light Grasp A measurement of the brightness a telescope can make a view. Light Grasp is the ratio between the area of a telescope's aperture and the area of a human dark-adapted (scotopic) pupil.

Light Loss - the percentage of light not transmitted by an optical system, compared to the brightness of the image entering that system.

Light Pollution Reduction (LPR) Filter A telescope filter that blocks the light of mercury and sodium vapor street lights, thus allowing faint nighttime celestial objects to be seen and photographed from cities.

Light Scatter - the reflection and loss of internal light in an optical system caused by the light deviating from its perfect path through the system. This is caused by reflective surfaces and optical inaccuracies in the optical train.

Light Transmission - the percentage of light making it through an optical system. Higher is better.

Light Year An astronomical unit of measure equal to the distance light travels in a year, approximately 5.9 trillion miles.

Limb The outer edge or border of a planet or other celestial body.

Local Group A small group of about three dozen galaxies of which our own Milky Way galaxy is a member.

Long Eye Relief - when the eye can be held well back from the eyepiece and still see the whole field of view, this is referred to as long eye relief. This is especially important for those who must wear glasses when observing (those with severe astigmatism).

Longitudinal Chromatic Aberration: the dioptric separation between the shortest and longest measured wavelengths along the axis of the lens. It occurs when the focal length of a lens is wavelength dependent. In other words, this is on-axis chromatic aberration.

LP - Light Pollution - scattered light in the nighttime atmosphere of the Earth caused by the use of improperly-designed exterior lighting that broadcasts its light up instead of down.

Luminosity The amount of light emitted by a star.

Lunar Having to do with the Moon

Lunar Eclipse A phenomenon that occurs when the Moon passes into the shadow of the Earth. A partial lunar eclipse occurs when the Moon passes partially into the umbra or the penumbra (partial shadow). In a total lunar eclipse, the Moon passes completely into the Earth's umbra (total shadow).

Lunar Month The average time between successive new or full moons. A lunar month is equal to 29 days 12 hours 44 minutes. Also called a synodic month.

Lunation The interval of a complete lunar cycle, between one new Moon and the next. A lunation is equal to a lunar month.

<< Prev Table of Contents Next >>

ASTRONOMICAL BOOKS

Tell Friend  

(112 Items) 1 2 3 4 5 6 7 8  Next Gallery View Click here for List Display
Sort By: Price | New | Brand | Category | Name
Agena Astro Products - The Great Atlas of the Sky, Jubilee Edition
New
Agena Astro Products - The Great Atlas of the Sky, Jubilee Edition
Item No. 786-20000

Agena Astro Products BOOKS The Great Atlas of the Sky by P.Brych
 
Our Price: $239.00
Buy Agena Astro Products - The Great Atlas of the Sky, Jubilee Edition
 

Sun Observer's Guide, Firefly Books
New
Sun Observer's Guide, Firefly Books
Item No. 896-23211
Manuf. No. Firefly 978-1-55297-941-9

A practical reference for how and why to view our nearest star. This book can start you making worthwhile observations.
 
Our Price: $14.95
Buy Sun Observer's Guide, Firefly Books
 

The History of Astronomy, Firefly Books
New
The History of Astronomy, Firefly Books
Item No. 896-23210
Manuf. No. Firefly 978-1-55407-537-9

This extraordinary book traces humans' interaction with the endless wonders of the night sky.
 
Our Price: $29.95
Buy The History of Astronomy, Firefly Books
 

Stargazing with a Telescope, Firefly Books
New
Stargazing with a Telescope, Firefly Books
Item No. 896-23208
Manuf. No. Firefly 978-1-55407-577-5

Stargazing with a Telescope is a practical guide that demystifies the process of buying and using a telescope.
 
Our Price: $19.95
Buy Stargazing with a Telescope, Firefly Books
 

Stargazing with Binoculars, Firefly Books
New
Stargazing with Binoculars, Firefly Books
Item No. 896-23207
Manuf. No. Firefly 978-1-55407-368-9

A practical, concise beginner's guide to viewing the night sky through binoculars
 
Our Price: $19.95
Buy Stargazing with Binoculars, Firefly Books
 

300 Astronomical Objects: A Visual Reference to the Universe, Firefly Books
300 Astronomical Objects: A Visual Reference to the Universe, Firefly Books
Item No. 896-23206
Manuf. No. Firefly 978-1-55407-175-3

A handy and comprehensive reference to the 300 most interesting celestial objects. This book provides a tour through the galaxy.
 
Our Price: $29.95
Buy 300 Astronomical Objects: A Visual Reference to the Universe, Firefly Books
 

Moon Observer's Guide, Firefly Books
Moon Observer's Guide, Firefly Books
Item No. 896-23203
Manuf. No. Firefly 978-1-55297-888-7

Moon Observer's Guide offers practical guidance to amateur astronomers viewing Earth's only natural satellite.
 
Our Price: $14.95
Buy Moon Observer's Guide, Firefly Books
 

Night Sky Atlas: The Moon, Planets, Stars and Deep Sky Objects, Firefly Book
Night Sky Atlas: The Moon, Planets, Stars and Deep Sky Objects, Firefly Book
Item No. 896-10719
Manuf. No. Firefly 978-1-55407-026-8

This Firefly book is a very nice introduction to astronomy for beginners.
 
Our Price: $29.95
Buy Night Sky Atlas: The Moon, Planets, Stars and Deep Sky Objects, Firefly Book
 

Software Bisque TheSkyX Professional Edition for Mac
Free Shipping
Software Bisque TheSkyX Professional Edition for Mac
Item No. 773-55161
Manuf. No. Software Bisque SKYX_PRO_MAC

TheSkyX Professional Edition for Mac is the next major release in TheSky's 25+ year history
 
Our Price: $349.00
Buy Software Bisque TheSkyX Professional Edition for Mac
 

Software Bisque TheSkyX Professional Edition for Windows
Free Shipping
Software Bisque TheSkyX Professional Edition for Windows
Item No. 773-55160
Manuf. No. Software Bisque SKYX_PRO_WIN

TheSkyX Professional for Windows will get you charged up about your passion. Explore, engage, enjoy while getting the most from your observing sessions.
 
Our Price: $349.00
Buy Software Bisque TheSkyX Professional Edition for Windows
 

Sky & Telescope - Sky Atlas 2000.0 Companion, 2nd Edition
Sky & Telescope - Sky Atlas 2000.0 Companion, 2nd Edition
Item No. 846-10899
Manuf. No. Sky Publishing 46956

This essential reference features an alphabetical listing of every deep sky object plotted in Sky Atlas 2000.00.
 
Our Price: $29.95
Buy Sky & Telescope - Sky Atlas 2000.0 Companion, 2nd Edition
 

Sky & Telescope - SKY ATLAS 2000.0 DESK UNLAMINATED
Sky & Telescope - SKY ATLAS 2000.0 DESK UNLAMINATED
Item No. 846-10898
Manuf. No. Sky Publishing 46883

Includes close-up charts of such areas as the celestial poles and the Virgo-Coma galaxy region, as well as an acetate coordinate-grid overlay for determining accurate positions
 
Our Price: $34.95
Buy Sky & Telescope - SKY ATLAS 2000.0 DESK UNLAMINATED
 

Sky & Telescope - SKY ATLAS 2000.0 FIELD LAMINATED
Eligible for Rewards
Sky & Telescope - SKY ATLAS 2000.0 FIELD LAMINATED
Item No. 846-10895
Manuf. No. Sky Publishing 46921

The standard against which all other star atlases are measured, each version of Sky Atlas 2000.0 contains 26 charts covering the whole sky and showing 81,312 single, multiple, and variable stars of magnitude of 8.5 and brighter and 2,700 deep-sky objects
 
Our Price: $69.95
Buy Sky & Telescope - SKY ATLAS 2000.0 FIELD LAMINATED
 

Sky & Telescope: SKY ATLAS 2000.0 FIELD UNLAMINATED
Sky & Telescope: SKY ATLAS 2000.0 FIELD UNLAMINATED
Item No. 846-10890
Manuf. No. Sky Publishing 46891

Field Version: Stars and deep sky objects are white on a black background. Unbound and printed on heavy paper
 
Our Price: $34.95
Buy Sky & Telescope: SKY ATLAS 2000.0 FIELD UNLAMINATED
 

Sky & Telescope - Astronomy Library Sky Atlas 2000.0 Deluxe Edition
Eligible for Rewards
Sky & Telescope - Astronomy Library Sky Atlas 2000.0 Deluxe Edition
Item No. 846-10880
Manuf. No. Sky Publishing 46875

Sky Atlas 2000.0 Deluxe Edition contains 26 charts showing close to 85,000 objects (stars and deep sky objects) down to magnitude 8.5
 
Our Price: $69.95
Buy Sky & Telescope - Astronomy Library Sky Atlas 2000.0 Deluxe Edition
 

1 2 3 4 5 6 7 8  Next
 


Scope City 100% Satisfaction Guarantee

Scope City unconditionally guarantees that you will be 100% satisfied with your mail order purchase, or just
return the merchandise in original condition within 15 days for a Full Refund, less shipping and handling charges!