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J -
Jovian Planets
K -
Kuiper Belt
L -
(LY)
Light-Year
M -
Magnitude
Meridian
Messier
N -
Nebula
North Celestial Pole
Nova
O -
Open Cluster
P -
Parallax
Parfocal
Parsec
Point Source
R -
Reflector
Resolution
Right Ascension: (RA)
S -
Schmidt Telescope
Any of the four gas giant planets that are at a greater distance form the sun than the terrestrial
planets.
A region beyond the orbit of Neptune extending to about 1000 AU which is a source of many short
period comets.
A light-year is the distance light traverses in a vacuum in one year at the speed of 299,792 km/ sec.
With 31,557,600 seconds in a year, the light-year equals a distance of 9.46 X 1 trillion km (5.87 X
1 trillion mi).
Magnitude is a measure of the brightness of a celestial body. The brightest stars are assigned
magnitude 1 and those increasingly fainter from 2 down to magnitude 5. The faintest star that can
be seen without a telescope is about magnitude 6. Each magnitude step corresponds to a ratio of
2.5 in brightness. Thus a star of magnitude 1 is 2.5 times brighter than a star of magnitude 2, and
100 times brighter than a magnitude 5 star. The brightest star, Sirius, has an apparent magnitude of
-1.6, the full moon is -12.7, and the Sun's brightness, expressed on a magnitude scale, is -26.78.
The zero point of the apparent magnitude scale is arbitrary.
A reference line in the sky that starts at the North celestial pole and ends at the South celestial pole
and passes through the zenith. If you are facing South, the meridian starts from your Southern
horizon and passes directly overhead to the North celestial pole.
A French astronomer in the late 1700's who was primarily looking for comets. Comets are hazy
diffuse objects and so Messier cataloged objects that were not comets to help his search. This
catalog became the Messier Catalog, M1 through M110.
Interstellar cloud of gas and dust. Also refers to any celestial object that has a cloudy appearance.
The point in the Northern hemisphere around which all the stars appear to rotate. This is caused by
the fact that the Earth is rotating on an axis that passes through the North and South celestial poles.
The star Polaris lies less than a degree from this point and is therefore referred to as the "Pole
Star".
Although Latin for "new" it denotes a star that suddenly becomes explosively bright at the end of
its life cycle.
One of the groupings of stars that are concentrated along the plane of the Milky Way. Most have
an asymmetrical appearance and are loosely assembled. They contain from a dozen to many
hundreds of stars.
Parallax is the difference in the apparent position of an object against a background when viewed
by an observer from two different locations. These positions and the actual position of the object
form a triangle from which the apex angle (the parallax) and the distance of the object can be
determined if the length of the baseline between the observing positions is known and the angular
direction of the object from each position at the ends of the baseline has been measured. The
traditional method in astronomy of determining the distance to a celestial object is to measure its
parallax.
Refers to a group of eyepieces that all require the same distance from the focal plane of the
telescope to be in focus. This means when you focus one parfocal eyepiece all the other parfocal
eyepieces, in a particular line of eyepieces, will be in focus.
The distance at which a star would show parallax of one second of arc. It is equal to 3.26 light-
years, 206,265 astronomical units, or 30,8000,000,000,000 km. (Apart from the Sun, no star lies
within one parsec of us.)
An object which cannot be resolved into an image because it to too far away or too small is
considered a point source. A planet is far away but it can be resolved as a disk. Most stars cannot
be resolved as disks, they are too far away.
A telescope in which the light is collected by means of a mirror.
The minimum detectable angle an optical system can detect. Because of diffraction, there is a limit
to the minimum angle, resolution. The larger the aperture, the better the resolution.
The angular distance of a celestial object measured in hours, minutes, and seconds along the
Celestial Equator eastward from the Vernal Equinox.
Rated the most important advance in optics in 200 years, the Schmidt telescope combines the best
features of the refractor and reflector for photographic purposes. It was invented in 1930 by
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