F
F
-
o mirror) and the point at which the image of an object at infinity is
gth divided by the aperture of the mirror or lens is termed the focal
Jovian Planets
K -
ar (ly)
5.87 X 1
Magnitude ude is a measure of the brightness of a celestial body. The brightest stars are assigned
down to magnitude 5. The faintest star that can be
ds to a ratio of 2.5 in
itude 2, and 100 times
irius, has an apparent magnitude of -1.6, the
ness, expressed on a magnitude scale, is -26.78. The zero
Meridian pole and ends at the South celestial pole
directly overhead to the North celestial pole.
jects that were not comets to help his search. This
N -
Nebula
h Celestial Pole Northern hemisphere around which all the stars appear to rotate. This is caused by
.
Nova
O -
Open Cluster
by
a
if
lar direction of the
easured. The traditional method in
astronomy of determining the distance to a celestial object is to measure its parallax.
focus.
,
as a disk. Most stars cannot
be resolved as disks, they are too far away.
-
eflector A telescope in which the light is collected by means of a mirror.
cal length The distance between a lens (or
brought to focus. The focal len
ratio.
J -
Any of the four gas giant planets that are at a greater distance form the sun than the terrestrial
planets.
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-Ye
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 (
trillion mi).
M -
Magnit
magnitude 1 and those increasingly fainter from 2
seen without a telescope is about magnitude 6. Each magnitude step correspon
ghter than a star of magn
brightness. Thus a star of magnitude 1 is 2.5 times bri
brighter than a magnitude 5 star. The brightest star, S
full moon is -12.7, and the Sun's bright
point of the apparent magnitude scale is arbitrary.
A reference line in the sky that starts at the North celestial
and passes through the zenith. If you are facing South, the meridian starts from your Southern
horizon and passes
Messier A French astronomer in the late 1700’s who was primarily looking for comets. Comets are hazy
diffuse objects and so Messier cataloged ob
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
Nort
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.
P -
Parallax Parallax is the difference in the apparent position of an object against a background when viewed
an observer from two different locations. These positions and the actual position of the object form
triangle from which the apex angle (the parallax) and the distance of the object can be determined
the length of the baseline between the observing positions is known and the angu
object from each position at the ends of the baseline has been m
Parfocal 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
Parsec 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
Point Source
R
R
43
