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
Inferior Conjunction A conjunction of an inferior planet
that occurs when the planet is lined up directly between the Earth and
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
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.
John Dobson. Inventor of the Dobsonian. See also Dob.
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
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.
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
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
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
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
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
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.