Magellanic Clouds Two small, irregular galaxies found
just outside, and orbiting, our own Milky Way galaxy. The Magellanic Clouds
are visible in the skies of the southern hemisphere.
Magnetic Field A condition found in the region around
a magnet or an electric current, characterized by the existence of a detectable
magnetic force at every point in the region and by the existence of magnetic
Magnetic Pole Either of two limited regions in a magnet
at which the magnet's field is most directional.
Magnification A measurable increase in the apparent
size of an object. Magnification = (focal length of a telescope) / (focal
length of the eyepiece).
Magnitude The degree of brightness of a star or other
object in the sky according to a scale on which the brightest star has
a magnitude -1.4 and the faintest visible star has magnitude 6. Sometimes
referred to as apparent magnitude. In this scale, each number is 2.5 times
the brightness of the previous number. Thus a star with a magnitude of
1 is 100 times brighter than on with a visual magnitude of 6. This scale
is a modern derivation of the ancient astronomer Ptolemy, who divided
the stars in the sky into 6 magnitudes, the brightest being "First", and
the dimmest "Sixth". The smaller this number is, the brighter is the object
Main Belt The area between Mars and Jupiter where most
of the asteroids in our solar system are found.
Major Planet A name used to describe any planet that
is considerably larger and more massive than the Earth, and contains large
quantities of hydrogen and helium. Jupiter and Saturn are examples of
Mak - Maksutov-Cassegrain Telescope
Maksutov-Cassegrain - A catadioptric telescope design
characterized by a thick deeply curved Corrector Plate , all-spherical
mirrors, and usually an f15 focal ratio.
Maksutov-Newtonian: a telescope comprising a meniscus
corrector, concave primary, and flat secondary, assembled into a Newtonian
configuration. Exhibits coma, though not as much as a Schmidt-Newtonian.
Marechal's Criterion In optical systems, the final wave
front aberration tolerance of 0.25-wave peak-to-valley and 0.07-wave(1/14)
root-mean-square. Similar to the Rayleigh Limit, but also specifies a
smooth wave front.
Mass A measure of the total amount of material in a
body, defined either by the inertial properties of the body or by its
gravitational influence on other bodies.
Matter A word used to describe anything that contains
Meridian An imaginary circle drawn through the North
and South poles of the celestial sphere.
Mesopic - a condition of the eye where the ambient light
is starting to turn the cones in the eye¡¯s retina on and we have partial
color vision. Most people have this when looking at the night sky after
becoming completely dark-adapted..
Messier Object - A non-stellar celestial object listed
in the Messier Catalog, compiled in the 18th Century.
Meteor A small particle of rock or dust that burns away
in the Earth's atmosphere. Meteors are also referred to as shooting stars.
Meteor Shower An event where a large number of meteors
enter the Earth's atmosphere from the same direction in space at nearly
the same time. Most meteor showers take place when the Earth passes through
the debris left behind by a comet.
Meteorite An object, usually a chunk or metal or rock,
which survives entry through the atmosphere to reach the Earth's surface.
Meteors become meteorites if they reach the ground.
Milky Way - Our home galaxy. We see it at night as a
circle of faint light that goes 360 degrees around the sky. It is only
visible in a dark sky.
Minor Planet - Another name used to describe a large
Minus Violet Filter - a filter that removes the color
of light most poorly focused by a two-element achromatic refractor lens
Mirror Coatings - Aluminum or dielectric coatings deposited
on first-surface mirrors to greatly enhance reflectivity.
MN - Maksutov-Newtonian Telescope
Monocentric: a term referring to a lens set which has
their radii of curvatures at the same location, or at nearly the same
location. Also refers to an early type of eyepiece.
Monochromatic Aberrations: spherical aberration, coma,
astigmatism, curvature of field, and distortion are the monochromatic
aberrations. They were analyzed by Seidel in the 1850's.
Monochromatic Light - Light of a single wavelength.
Moondogs - reflections of the Moon, these are bright
spots in the upper atmosphere (caused by ice crystals) that precede and
follow the Moon in the sky.
MOT - Mirror On Top. ATM term for mirror grinding, where
the mirror is on top of the grinding tool. See also TOT.
Mount - a mechanical device that supports the optical
tube assembly of a telescope. There are many configurations, but only
2 basic types: alt/az and equatorial.
Multi-coated: the air to glass surfaces of lenses that
are antireflection coated with more than one layer of coatings. In the
past, this term was distinguished from "fully multi-coated," where "fully"
meant every air-glass surface was so coated, while multi-coated could
mean that some surfaces were left uncoated. This difference is no longer
maintained; e.g., some manufacturers use "multi- coated" to refer to "fully
multi-coated". Additionally, for some applications singly-coated optics
are preferred. In general, a meaningless term, somewhat perpetuated by
out of date information, occasional marketing hype, and sometimes misplaced
brand loyalty. Today, nearly ALL high-quality eyepieces are multi-coated.
Mylar - an aluminized acetate film that is quite flexible.
It is often used as a solar filter material for telescopes.
Myopia - near-sightedness. You can see near objects
well, but not far ones.
Nadir - the opposite of zenith - the bottom-most point
of the celestial sphere around you.
Nagler, Albert: foremost telescope ocular designer of
the latter half of the 20th century, and beginning of the 21st century.
He is best known for designs which offer large fields of view with good
correction of off-axis astigmatism and chromatic aberration, in some cases
out to 82 degrees of apparent field. Nagler's designs do not use any aspheric
surfaces, which reduces manufacturing costs. While many opticians have
designed multitudes of such oculars, most of them remain inventions on
paper only; Al Nagler's company, TeleVue, manufactures many of Nagler's
designs. He deserves fame, as his Ultrawidefield designs were the first
commercially successful of the UWA designs.
Nagler Eyepiece - A highly-corrected, ultrawidefield
eyepiece manufactured by TeleVue Optics.
Naked Eye - the eye used without optical aid (glasses
Narrowfield - an apparent field of view of 50 degrees
or less. Most inexpensive eyepieces are narrowfields.
NEAF - Northeast Astronomy Forum & Telescope Show.
Nebula A cloud of dust and gas in space, usually illuminated
by one or more stars. Nebulae represent the raw material the stars are
Nebular Filters - These are restricted bandwidth filters
that target specific frequencies of light, used to enhance views of dim
targets such as nebulae.
Negative focal length: a lens or mirror which diverges
light is said to have a negative focal length. If a collimated beam of
light is passed through such an optic, it will diverge; if the angle of
divergence is traced back through the optic to that angle's intersection,
the negative of the distance between that point and the optic is its focal
length. Common optical systems which have negative focal lengths include
the Barlow lens and the secondary mirror on Cassegrain systems.
Negative Lens A lens that cannot form an image when
used alone, but can be used together with positive lenses to correct their
aberrations, to amplify an optical system, or to relocate an image.
Negative Lens Projection Photography - The photographic
technique of using a telenegative amplifying lens to enlarge the image
formed by a telescope and to project the image directly into the camera.
NELM - Naked Eye Limiting Magnitude. This refers to
the magnitude of the faintest star that can be seen by the naked eye in
a dark, moonless, sky.
Neutral Density Filters - Gray Filters used to reduce
light from bright targets like the moon without introducing false color.
Neutron Star A compressed core of an exploded star made
up almost entirely of neutrons. Neutron stars have a strong gravitational
field and some emit pulses of energy along their axis. These are known
Newt - Newtonian Reflector
Newtonian Reflector - A telescope employing a paraboloidal
primary and a smaller, flat diagonal mirror to form images: the first
practical reflecting optical telescope, invented by Isaac Newton, consisting
of a concave primary mirror and a flat secondary mirror that diverts light
out the side of the tube. For best correction on-axis, the Newtonian is
made with a paraboloidal primary mirror. Small Newtonians of around f/14
or longer can give acceptable performance with a spherical mirror. Spherical
Newtonians with an aperture stop at the radius of curvature can be made
coma-free. See also coma.
NGC New General Catalog of Non-Stellar Astronomical
Objects. A catalog of all visible deep-sky objects known at the time (late
19th Century) it was complied. You can find a corrected list free for
download at http://www.ngcic.org/
Noctilucent Clouds - high clouds composed of ice crystals;
visible long after sunset and seemingly illuminated by the Sun.
Nova A star that flares up to several times its original
brightness for some time before returning to its original state. Often
a convulsive explosion of the atmosphere of a very old star.