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multiple systems. Systems with individual
components that can be seen separately by
a telescope are called visual binaries or visual
multiples. The nearest “star” to our solar
system, Alpha Centauri, is actually our nearest
example of a multiple star system, it consists
of three stars, two very similar to our Sun and
one dim, small, red star orbiting around one
another.
C –
Celestial The projection of the Earth’s equator
Equator on to the celestial sphere. It divides the sky
into two equal hemispheres.
Celestial pole The imaginary projection of Earth’s rotational
axis north or south pole onto the
celestial sphere.
Celestial An imaginary sphere surrounding the Earth,
Sphere concentric with the Earth’s center.
Collimation The act of putting a telescope’s optics into
perfect alignment.
D –
Declination The angular distance of a celestial body
(DEC) north or south of the celestial equator. It may
be said to correspond to latitude on the
surface of the Earth.
E –
Ecliptic The projection of the Earth’s orbit on to the
celestial sphere. It may also be defined as
“the apparent yearly path of the Sun against
the stars.”
Equatorial A telescope mounting in which the instrument
mount is set upon an axis which is parallel to the
axisoftheEarth;theangleoftheaxismustbe
equal to the observer’s latitude.
F –
Focal length Thedistancebetweenalens(ormirror)and
the point at which the image of an object at
infinity is brought to focus. The focal length
divided by the aperture of the mirror or lens is
termed the focal ratio.
G –
GoTo Term used to refer to a computerized
telescopeortotheactofslewing(moving)a
computerized telescope.
J –
Jovian Planets Any of the four gas giant planets that are
at a greater distance form the sun than the
terrestrial planets.
K –
Kuiper Belt A region beyond the orbit of Neptune
extending to about 1000 AU which is a source
of many short period comets.
L –
Light–Year (ly) A light–year is the distance light traverses in a
vacuum in one year at the speed of 186,000
mi/sec.(299,792km/sec.)With31,557,600
seconds in a year, the light–year equals a
distanceof5.88trillionmiles(9.46trillionkm).
M –
Magnitude 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.
Meridian 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.
Messier 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.
N –
Nebula Interstellar cloud of gas and dust. Also
refers to any celestial object that has a
cloudy appearance.
North Celestial The point in the Northern hemisphere around
Pole 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”.
Nova Although Latin for “new” it denotes a star that
suddenly becomes explosively bright at the
end of its life cycle.
O –
Open Cluster 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.
P –
Parallax 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
fromwhichtheapexangle(theparallax)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.
