ORION TELESCOPES & BINOCULARS StarBlast AutoTracker 8983 User manual

OrionTelescopes.com
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Providing Exceptional Consumer Optical Products Since 1975
Orion®StarBlast™80mm
AutoTracker™
#8983
IN 488 Rev. A 05/13
INSTRUCTION MANUAL

2
Introduction
Congratulations on your purchase of the Orion StarBlast tele-
scope!
Take time to read through this manual before embarking on
your journey through the heavens.
Please read the separate AutoTracker Mount Manual (IN 489)
for all information relating to the mount and its accessories.
Your StarBlast telescope is designed to give you years of fun
and exciting astronomical observations. However, there are
a few things to consider before using your telescope that will
ensure your safety and protect your equipment.
Parts List
Optical Tube Assembly
EZ Finder II Reflex Sight (with bracket)
Super 25mm Eyepiece
Super 10mm Eyepiece
90 degree Star Diagonal
Telescope Dust Cap
Attaching the Diagonal
Attach the 90˚ star diagonal to the optical tube. First remove
the caps from the diagonal and unthread the cover on the rear
of the telescope . The knurled ring on the diagonal connects
to the threads on the rear of the telescope. Tighten this ring
firmly. If you wish to change the orientation of the diagonal
for a more comfortable viewing angle, you must first loosen
the knurled ring on the diagonal. Rotate the diagonal to the
desired viewing angle, and retighten the knurled ring to lock
the diagonal into place (Figure 2).
The Eyepieces
The eyepiece, or ocular, is the optical element that magnifies
the image focused by the telescope. The eyepiece fits directly
into the diagonal. The 1.25" designation refers to the barrel
diameter of the eyepieces.
To install one of the included eyepieces:
1. Loosen the two thumbscrews on the diagonal.
2. Slide the barrel of the eyepiece into the diagonal.
3. Tighten the thumbscrews to hold the eyepiece in place.
To remove the eyepiece, loosen the thumbscrews on the diag-
onal and slide the eyepiece out.
Eyepieces are commonly referred to by their focal length and
barrel diameter. The focal length of each eyepiece is typically
printed on the eyepiece body. For example this telescope ships
with two 1.25" diameter eyepieces; a 25mm and a 10mm. The
longer the focal length (i.e., the larger the number), the lower
the eyepiece power or magnification; and the shorter the focal
length (i.e., the smaller the number), the higher the magnifi-
cation. Generally, you will use low-to-moderate power when
viewing. For more information on how to determine power, see
the section “Calculating Magnification.”
WARNING:
• NeverlookdirectlyattheSunwiththenaked
eyeorwithatelescope–unlessyouhaveaproper
solarfilterinstalledoverthefrontofthetelescope!
Otherwise,permanent,irreversibleeyedamage
mayresult.
• Neveruseyourtelescopetoprojectanimageof
theSunontoanysurface.Internalheatbuild-up
candamagethetelescopeandanyaccessories
attachedtoit.
• NeveruseaneyepiecesolarfilteroraHerschel
wedge.Internalheatbuild-upinsidethetelescope
cancausethesedevicestocrackorbreak,
allowingunfilteredsunlighttopassthroughto
theeye.
• Neverleavethetelescopeunsupervised,either
whenchildrenarepresentoradultswhomaynot
befamiliarwiththecorrectoperatingprocedures
ofyourtelescope.
Figure 1. In the box: Parts of the StarBlast 80mm.
Figure 2. The knurled ring of the diagonal connects to the
threads on the rear of the optical tube. To change the viewing
angle, loosen the knurled ring, rotate the diagonal, and then
retighten the ring.
Knurled ring

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Focusing
Using the lower power eyepiece (25mm) inserted and secured
with the thumbscrews, aim the optical tube so the front end
is pointing in the general direction of an object at least 1/4-
mile away. With your fingers, slowly rotate the focus knob until
the object comes into sharp focus. A good method to ensure
you’ve hit the exact focus point is go a little bit beyond sharp
focus until the image starts to blur again, then reverse the
rotation of the knob and stop when sharp focus has been
achieved again.
Installing the EZ Finder II
Slide the base of the EZ Finder II bracket into the dovetail
holder that is pre-installed on the optical tube. The EZ Finder
II should be oriented so that the sight tube is facing the front
of the telescope (Figure 3). Tighten the thumbscrew on the
dovetail holder to secure the EZ Finder II in place.
The EZ Finder II works by projecting a tiny red dot (it is not
a laser beam) onto a lens mounted in the front of the unit
(Figure 4). When you look through the EZ Finder II, the red dot
will appear to float in space, helping you to pinpoint your target
object. The red dot is produced by a light-emitting diode (LED)
near the rear of the sight. A 3-volt lithium battery provides the
power for the diode.
NOTE: If it is present, remove the thin plastic battery shield
tab (not shown) from the battery compartment prior to use
and discard it.
Turn the power knob (Figure 5) clockwise until you hear the
“click” indicating that power has been turned on. Look through
the back of the reflex sight with both eyes open to see the
red dot. Position your eye at a comfortable distance from the
back of the sight. In daylight you may need to cover the front
of the sight with your hand to be able to see the dot, which
is purposefully quite dim. The intensity of the dot is adjusted
by turning the power knob. For best results when stargazing,
use the dimmest possible setting that allows you to see the
dot without difficulty. Typically a dimmer setting is used under
dark skies and a brighter setting is needed under light-polluted
skies or in daylight.
Aligning the EZ Finder II
For the EZ Finder II to work properly, it has to be aligned with
the telescope. When the two are aligned, a celestial object that
is centered on the EZ Finder II’s red dot should also appear
in the center of the telescope’s eyepiece. Alignment of the
EZ Finder II is easiest during daylight, before observing at
night. Aim the telescope at a distant object such as a tele-
phone pole or roof chimney and center it in the telescope’s
eyepiece. The object should be at least 1/4 mile away. Now
turn on the EZ Finder II and look through it. Without moving
the main telescope, use the EZ Finder II’s azimuth (left/right)
and altitude (up/down) adjustment knobs (Figure 5) to position
the red dot on the object in the eyepiece. When the red dot is
centered on the distant object, check to make sure that the
object is still centered in the telescope eyepiece. If it isn’t, re-
center it and adjust the EZ Finder II’s alignment again. When
the object is centered in the eyepiece and on the EZ Finder’s
red dot, the EZ Finder II is properly aligned with the telescope.
Figure 4. The EZ Finder II superimposes a tiny red dot on
the sky, showing right where the telescope is aimed.
Figure 3. Insert the EZ Finder II in its dovetail base in the
orientation shown and secure it with the thumbscrew.
Front
(open) end
of optical
tube
Dovetail
base
Thumbscrew
Figure 5. The EZ Finder II’s On/Off and adjustment knobs.
Power knob
Azimuth
adjustment
knob
Battery
casing
Mounting bracket
Altitude
adjustment
knob
Slot for
battery
removal

4
Once aligned, EZ Finder II will usually hold its alignment even
after being removed and remounted. Otherwise, only minimal
realignment will be needed. At the end of your observing ses-
sion, be sure to turn off the power knob on the EZ Finder II.
Replacing the EZ Finder II Battery
Should the battery ever die, replacement 3-volt lithium batter-
ies are available from many retail outlets. Remove the old bat-
tery by inserting a small flat-head screwdriver into the slot on
the battery casing (Figure 5) and gently prying open the case.
Then carefully pull back on the retaining clip and remove the
old battery. Do not over bend the retaining clip. Then slide the
new battery under the battery lead with the positive (+) end
facing down and replace the battery casing.
Telescope Basics
A telescope is an instrument that collects and focuses light.
The nature of the optical design determines how the light is
focused. Some telescopes, known as refractors, use lenses.
Other telescopes, known as reflectors, use mirrors.
The StarBlast 80mm is a refracting telescope.
Focusing
Once you have found an object in the telescope, turn the
focusing knob until the image is sharp. To achieve a truly sharp
focus, never look through glass windows or across objects that
produce heat waves, such as asphalt parking lots.
For astronomical viewing, out of focus star images are very dif-
fuse, making them difficult to see. If you turn the focus knob
too quickly, you can go right through focus without seeing the
image. To avoid this problem, your first astronomical target
should be a bright object (like the Moon or a planet) so that the
image is visible even when out of focus. It can even be helpful
to practice during the day on an object at least a mile away, i.e.,
at “infinity.”
Image Orientation
The image orientation of any telescope changes depending
on its optical design and how the eyepiece is inserted into the
telescope. A refractor used with a star diagonal, for astronomi-
cal viewing, will show an image that is right side up, but left-
right reversed. When observing through a reflector such as
the StarBlast 114mm, the image will appear upside down and
backwards. For this reason reflectors are not recommended
for daytime terrestrial observing. But since there is no “right
side up” in space, a reflector is fine for astronomical viewing.
Calculating Magnification
You can change the power of your telescope just by changing
the eyepiece (ocular). To determine the magnification of your
telescope, simply divide the focal length of the telescope by
the focal length of the eyepiece used.
Magnification is calculated as follows:
Telescope Focal Length = Magnification
Eyepiece Focal Length
For example, the StarBlast 80mm has a focal length of 350mm,
which when used with the supplied 25mm eyepiece yields:
350mm = 14x
25mm
The magnification provided by the 10mm eyepiece is:
350mm = 35x
10mm
Although the power is variable, each instrument under aver-
age skies has a limit to the highest useful magnification. The
general rule is 2x per millimeter of aperture. For example, the
StarBlast 80mm is so named for its objective lens, which has a
diameter of 80mm. So 80mm x 2 = 160. Thus, 160x is the high-
est magnification one can normally achieve under ideal seeing
conditions. Although this is the maximum useful magnification,
most observing will yield best results at lower powers.
Determining Field of View
Determining the field of view is important if you want to get
an idea of the angular size of the object you are observing. To
calculate the actual field of view, divide the apparent field of
the eyepiece (supplied by the eyepiece manufacturer) by the
magnification. In equation format, the formula looks like this:
Apparent Field of Eyepiece = True Field
Magnification
As you can see, before determining the field of view, you must
calculate the magnification. Using the example in the previous
section, we can determine the field of view using the same
25mm eyepiece.
The 25mm eyepiece has an apparent field of view of 49°.
Divide 49° by the magnification, which is 14 power. This yields
an actual field of view of 3.5°.
49 = 3.5° True Field of view
14
The 10mm eyepiece has an apparent field of view of 52°.
Divide 52° by the magnification, which is 35 power. This yields
an actual field of view of 1.49°.
52 = 1.49° True Field of view
35
To convert degrees to feet at 1,000 yards, which is more useful
for terrestrial observing, simply multiply by 52.5.
The 25mm eyepiece produces a linear field width of 183.75
feet at a distance of one thousand yards (3.5° X 52.5).
The 10mm eyepiece produces a linear field width of 78.23 feet
at a distance of one thousand yards (1.49° X 52.5).
General Observing Hints
When working with any optical instrument, there are a few
things to remember to ensure you get the best possible image:
• Never look through window glass. Glass found in household
windows is optically imperfect, and as a result, may vary
in thickness from one part of a window to the next. This
inconsistency can and will affect the ability to focus your
telescope. In most cases you will not be able to achieve a
truly sharp image, while in some cases; you may actually
see a double image.

5
• Never look across or over objects that are radiating heat
waves. This includes asphalt parking lots on hot summer
days or building rooftops.
• Hazy skies, fog, and mist can also make it difficult to
focus. The amount of detail seen under these conditions is
greatly reduced.
• If you wear corrective lenses (specifically, glasses),
you may want to remove them when observing with
an eyepiece attached to the telescope. When using a
camera, however, you should always wear corrective
lenses to ensure the sharpest possible focus. If you have
astigmatism, corrective lenses must be worn at all times.
Celestial Observing
With your telescope set up, you are ready to use it for observ-
ing. This section covers visual observing hints for both solar
system and deep-sky objects as well as general observing
conditions that will affect your ability to observe.
Observing the Moon
Often, it is tempting to look at the Moon when it is full. At this
time, the face we see is fully illuminated and its light can be
overpowering. In addition, little or no contrast can be seen dur-
ing this phase.
One of the best times to observe the Moon is during its partial
phases (at crescent phases and around the time of first or third
quarter). Long shadows reveal a great amount of detail on the
lunar surface. At low power you will be able to see most of the
lunar disk at one time. Change to higher power (magnification)
to focus in on a smaller area.
Lunar Observing Hints
• To increase contrast and bring out detail on the lunar
surface, use eyepiece filters. A yellow filter works well at
improving contrast while a neutral density or polarizing filter
will reduce overall surface brightness and glare.
Observing the Planets
Other fascinating targets include the five naked eye planets.
You can see Venus go through its lunar-like phases. Mars can
reveal a host of surface detail and one, if not both, of its polar
caps. You will be able to see the cloud belts of Jupiter and the
great Red Spot (if it is visible at the time you are observing).
In addition, you will also be able to see the moons of Jupiter
as they orbit the giant planet. Saturn, with its beautiful rings, is
easily visible at moderate power.
Planetary Observing Hints
• Remember that atmospheric conditions are usually the
limiting factor on how much planetary detail will be visible.
So, avoid observing the planets when they are low on the
horizon or when they are directly over a source of radiating
heat, such as a rooftop or chimney. See the “Seeing”
section later in this section.
• To increase contrast and bring out detail on the planetary
surface, try using color eyepiece filters.
Observing the Sun
Although overlooked by many amateur astronomers, solar
observation is both rewarding and fun. However, because
the Sun is so bright, special precautions must be taken when
observing our star so as not to damage your eyes or your tele-
scope.
Never project an image of the Sun through the telescope.
Tremendous heat build-up may result inside the optical tube.
This can damage the telescope and/or any accessories
attached to the telescope.
For safe solar viewing, use a solar filter that reduces the inten-
sity of the Sun’s light, making it safe to view. With a filter you
can see sunspots as they move across the solar disk and facu-
lae, which are bright patches seen near the Sun’s edge.
Solar Observing Hints
• The best time to observe the Sun is in the early morning or
late afternoon when the air is cooler.
• To center the Sun without looking into the eyepiece, watch
the shadow of the telescope tube until it forms a circular
shadow. There are also special “solar viewing” finder
devices available that are designed for aligning a telescope
with the Sun.
Observing Deep-Sky Objects
Deep-sky objects are simply those objects outside the bound-
aries of our solar system. They include star clusters, planetary
nebulae, diffuse nebulae, double stars and other galaxies out-
side our Milky Way galaxy. Most deep-sky objects have a large
angular size. Therefore, low-to-moderate power is all you need
to see them. Visually, they are too faint to reveal any of the
color seen in long exposure photographs. Instead, they appear
grayish. And, because of their low surface brightness, they
should be observed from a dark sky location whenever possi-
ble. Light pollution around large urban areas washes out most
nebulae making them difficult, if not impossible, to observe.
Light Pollution Reduction filters help reduce the background
sky brightness, thus increasing contrast.
Viewing Conditions
Viewing conditions affect what you can see through your tele-
scope during an observing session. Conditions include trans-
parency, sky illumination, and seeing. Understanding viewing
conditions and the effect they have on observing will help you
get the most out of your telescope.
Transparency
Transparency is the clarity of the atmosphere, which is affected
by clouds, moisture, and other airborne particles. Thick cumu-
lus clouds are completely opaque while cirrus can be thin,
allowing the light from the brightest stars through. Hazy skies
absorb more light than clear skies, making fainter objects hard-
er to see and reducing contrast on brighter objects. Aerosols
ejected into the upper atmosphere from volcanic eruptions
also affect transparency. Ideal conditions are when the night
sky is inky black.

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Sky Illumination
General sky brightening caused by the Moon, aurorae, natural
airglow, and light pollution greatly affects transparency. While
not a problem for the brighter stars and planets, bright skies
reduce the contrast of extended nebulae making them dif-
ficult, if not impossible, to see. To maximize your observing,
limit deep-sky viewing to moonless nights far from the light
polluted skies found around major urban areas. LPR filters
enhance deep-sky viewing from light polluted areas by block-
ing unwanted light while transmitting light from certain deep-
sky objects. You can, on the other hand, observe planets and
stars from light polluted areas or when the Moon is out, due to
their strong brightness.
Seeing
Seeing conditions refer to the stability of the atmosphere.
“Seeing” directly affects the amount of fine detail seen in
extended objects.The air in our atmosphere acts as a lens that
bends and distorts incoming light rays. The amount of bend-
ing depends on air density. Varying temperature layers have
different densities and, therefore, bend light differently. Light
rays from the same object arrive slightly displaced creating an
imperfect or smeared image. These atmospheric disturbanc-
es vary from time-to-time and place-to-place. The size of the
air parcels compared to your aperture determines the “see-
ing” quality. Under good seeing conditions, fine detail is visible
on the brighter planets like Jupiter and Mars, and stars are
pinpoint images. Under poor seeing conditions, images are
blurred and stars appear as blobs.
The conditions described here apply to both visual and photo-
graphic observations.
Telescope Maintenance
While your StarBlast telescope requires little maintenance,
there are a few things to remember that will ensure your tele-
scope performs at its best.
Care and Cleaning of the Optics
Any quality optical lens cleaning tissue and optical lens clean-
ing fluid specifically designed for multi-coated optics can be
used to clean the exposed lenses of your eyepieces. Never use
regular glass cleaner or cleaning fluid designed for eyeglass-
es. Before cleaning with fluid and tissue, blow any loose par-
ticles off the lens with a blower bulb or compressed air. Then
apply some cleaning fluid to a tissue, never directly on the
optics. Wipe the lens gently in a circular motion, then remove
any excess fluid with a fresh lens tissue. Oily fingerprints and
smudges may be removed using this method. Use caution;
rubbing too hard may scratch the lens. On larger lenses,
clean only a small area at a time, using a fresh lens tissue on
each area. Never reuse tissues.
To minimize the need to clean your telescope, replace all lens
covers once you have finished using it. This will prevent con-
taminants from entering the optical tube.
Specifications
Optical Diameter: 80mm diameter
Focal Length: 350mm
Focal Ratio: f/4.3
Eyepieces: Super 25mm, Super 10mm
Magnification with
supplied eyepieces: 14x, 35x
Glossary of Terms
A-
Absolute magnitude: The apparent magnitude that a star
would have if it were observed from a standard distance
of 10 parsecs, or 32.6 light-years. The absolute magnitude
of the Sun is 4.8. at a distance of 10 parsecs, it would just
be visible on Earth on a clear moonless night away from
surface light.
Airy disk: The apparent size of a star’s disk produced even
by a perfect optical system. Since the star can never be
focused perfectly, 84 per cent of the light will concentrate
into a single disk, and 16 per cent into a system of sur-
rounding rings.
Alt-Azimuth Mounting: A telescope mounting using two inde-
pendent rotation axes allowing movement of the instru-
ment in Altitude and Azimuth.
Altitude: In astronomy, the altitude of a celestial object is its
Angular Distance above or below the celestial horizon.
Aperture: The diameter of a telescope’s primary lens or mir-
ror; the larger the aperture, the greater the telescope’s
light-gathering power.
Apparent Magnitude: A measure of the relative brightness of
a star or other celestial object as perceived by an observer
on Earth.
Arc minute: A unit of angular size equal to 1/60 of a degree.
Arc second: A unit of angular size equal to 1/3,600 of a
degree (or 1/60 of an arc minute).
Asterism: A small unofficial grouping of stars in the night sky.
Asteroid: A small, rocky body that orbits a star.
Astrology: The pseudoscientific belief that the positions of
stars and planets exert an influence on human affairs;
astrology has nothing in common with astronomy.
Astronomical unit (AU): The distance between the Earth and
the Sun. It is equal to 149,597,900 km., usually rounded
off to 150,000,000 km.
Aurora: The emission of light when charged particles from the
solar wind slams into and excites atoms and molecules in
a planet’s upper atmosphere.
Azimuth: The angular distance of an object eastwards along
the horizon, measured from due north, between the astro-
nomical meridian (the vertical line passing through the
center of the sky and the north and south points on the

7
horizon) and the vertical line containing the celestial body
whose position is to be measured. .
B -
Binary Stars: Binary (Double) stars are pairs of stars that,
because of their mutual gravitational attraction, orbit
around a common center of mass. If a group of three or
more stars revolve around one another, it is called a mul-
tiple system. It is believed that approximately 50 percent
of all stars belong to binary or 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 Equator: The projection of the Earth’s 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 Sphere: An imaginary sphere surrounding the
Earth, concentric with the Earth’s center.
Collimation: The act of putting a telescope’s optics into per-
fect alignment.
D -
Declination (DEC): The angular distance of a celestial body
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 celes-
tial sphere. It may also be defined as “the apparent yearly
path of the Sun against the stars”.
Equatorial mount: A telescope mounting in which the instru-
ment is set upon an axis which is parallel to the axis of the
Earth; the angle of the axis must be equal to the observ-
er’s latitude.
F -
Focal length: The distance between a lens (or mirror) 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.
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 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).
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 pri-
marily 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 Cata-
log, M1 through M110.
N -
Nebula: Interstellar cloud of gas and dust. Also refers to any
celestial object that has a cloudy appearance.
North Celestial Pole: 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 pass-
es through the North and South celestial poles. The star
Polaris lies less than a degree from this point and is there-
fore 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 con-
centrated 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 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.
continued on back page

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copy of the original receipt) is required. This warranty is only valid in the country of purchase.
This warranty does not apply if, in Orion’s judgment, the instrument has been abused, mishandled, or
modified, nor does it apply to normal wear and tear. This warranty gives you specific legal rights. It is not
intended to remove or restrict your other legal rights under applicable local consumer law; your state or
national statutory consumer rights governing the sale of consumer goods remain fully applicable.
For further warranty information, please visit www.OrionTelescopes.com/warranty.
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 eye-
piece all the other parfocal eyepieces, in a particular line
of eyepieces, will be in focus.
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.)
Point Source: 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.
R -
Reflector: A telescope in which the light is collected by means
of a mirror.
Resolution: 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.
Right Ascension (RA): The angular distance of a celestial
object measured in hours, minutes, and seconds along
the Celestial Equator eastward from the Vernal Equinox.
S -
Sidereal Rate: This is the angular speed at which the Earth
is rotating. Telescope tracking motors drive the telescope
at this rate. The rate is 15 arc seconds per second or 15
degrees per hour.
T -
Terminator: The boundary line between the light and dark
portion of the moon or a planet.
U -
Universe: The totality of astronomical things, events, relations
and energies capable of being described objectively.
V -
Variable Star: A star whose brightness varies over time due to
either inherent properties of the star or something eclips-
ing or obscuring the brightness of the star.
W -
Waning Moon: The period of the moon’s cycle between full
and new, when its illuminated portion is decreasing.
Waxing Moon: The period of the moon’s cycle between new
and full, when its illuminated portion is increasing.
Z -
Zenith: The point on the Celestial Sphere directly above the
observer.
Zodiac: The zodiac is the portion of the Celestial Sphere that
lies within 8 degrees on either side of the Ecliptic. The
apparent paths of the Sun, the Moon, and the planets,
with the exception of some portions of the path of Pluto,
lie within this band. Twelve divisions, or signs, each 30
degrees in width, comprise the zodiac. These signs coin-
cided with the zodiacal constellations about 2,000 years
ago. Because of the Precession of the Earth’s axis, the
Vernal Equinox has moved westward by about 30 degrees
since that time; the signs have moved with it and thus no
longer coincide with the constellations.