Orion AstroView 55028 User manual

IN 673 05/22
Orion®AstroView™ 102mm
Equatorial Refractor Telescope
#55028
INSTRUCTION MANUAL
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may be reproduced, copied, modied or adapted, without the prior written consent of Orion Telescopes & Binoculars.
AN EMPLOYEE-OWNED COMPANY

2
I. Parts
Unpack all of the parts and lay them out on the oor. Make sure
all the parts listed below and shown in Figure 1 are present.
Save the shipping box and packaging material. In the unlikely
event that you need to return the mount, you must use the origi-
nal packaging.
Part Qty
A – Tripod 1
B – Equatorial mount 1
C – Accessory tray 1
D – Latitude adjustment T-bolt 1
E – Slow-motion cables 2
F – Counterweight shaft 1
G – Counterweight 1
H – Optical tube 1
I – EZ Finder II reex sight 1
J – Star diagonal 1
K – 25mm Plossl eyepiece, 1.25" 1
L – 10mm Plossl eyepiece, 1.25" 1
M – Dust cover 1
N – MoonMap 260 1
O – Allen wrench 1
Congratulations on your purchase of an Orion telescope. . Your new AstroView 102mm Equatorial Refractor Tele-
scope is a terric instrument designed to provide outstanding views of celestial wonders. These instructions will help you set up,
properly use, and care for your telescope. Please read them over thoroughly before getting started.
Figure 1. Components of the AstroView 102mm EQ Refractor
Table of Contents
I. Parts 2
II. Assembly 3
III. Preparing the Telescope for Operation 3
IV. Understanding and Using the
Equatorial Mount 5
V. Astronomical Observing 10
VI. Telescope Care and Maintenance 12
VII. Useful Optional Accessories 12
VIII. Specications 13
A
B
C
O
M
F
G
N
I
D
JKL
E
H
update

3
WARNING: Never look directly at the Sun
through your telescope or its nder scope—even
for an instant—without a professionally made
solar lter that completely covers the front of
the instrument, or permanent eye damage could
result. Young children should use this telescope
only with adult supervision.
II. Assembly
1. Spread the tripod (A) legs apart and stand the tripod on
the ground. You can extend the legs to the desired height
later using the leg lock knobs. For now just keep them fully
retracted.
2. Attach the accessory tray (C) by registering its center cutout
over the center of the tripod leg brace assembly (Figure
2A). Press the tray down and twist it until the tray tabs click
in place under the three retaining clips on the brace (2B).
3. Now you will attach the equatorial mount (B) to the tripod.
Place the base of the mount onto the tripod’s mounting plat-
form, then turn the mount attachment knob clockwise until
it’s tight (Figure 3).This secures the equatorial mount to the
tripod.
4. Next, thread the second latitude adjustment T-bolt (D) into
the hole in the mount base. (One T-bolt comes pre-installed;
the other one you must install yourself.) Figure 3 shows the
two installed latitude adjustment T-bolts.
5. Install the counterweight shaft (F) by threading it into the
counterweight shaft collar (Figure 4A).
6. Now remove the safety stop at the end of the shaft and slide
the counterweight (G) onto the shaft (Figure 4B). You may
have to loosen the counterweight lock knob to allow the
weight to slide onto the shaft. Once the counterweight is on
the shaft, replace the safety stop.
7. Attach the two slow-motion cables (E) to the right ascen-
sion (RA) and declination (Dec) gear shafts by threading the
collar on the gear shaft onto the cable until tight (Figure 5).
You can see where they attach in Figure 6.
Before installing the optical tube on the mount, ensure that the
RA and Dec lock knobs (Figure 6) are tightened so that the
mount won’t swivel accidentally when you’re attaching the opti-
cal tube.And of course make sure the counterweight is installed
on the counterweight shaft.
8. Make sure the two saddle clamp knobs are backed out suffi-
ciently to allow the dovetail bar to seat properly.Then lift the
optical tube (H) and set the dovetail mounting bar into the
mount’s saddle (Figure 7).When the dovetail bar is seated
in the saddle, tighten the two saddle clamp knobs until tight.
9. Next, you will install the EZ Finder II Reex sight (I). Slide
the foot of the EZ Finder II into the dovetail mounting shoe
as shown in Figure 8. Make sure the tab at the bottom of the
bracket inserts snugly into the corresponding notch in the
dovetail shoe. Then tighten the thumbscrew on the shoe.
The EZ Finder II should be oriented so that the sight tube is
facing the front of the telescope, as in Figure 8.
A star diagonal is used to divert the light at a right angle from the
light path of the telescope. This allows you to observe in posi-
tions that are more comfortable than if you were to look straight
through the telescope.
10. To attach the star diagonal (J), remove the protective dust
cap from the 1.25" accessory adapter. Loosen the two
thumbscrews on the adapter and slide the chrome portion
of the star diagonal into it (Figure 9). Then retighten the
thumbscrews to hold the star diagonal in place.
An eyepiece is the optical element that magnies the image
focused by the telescope.The eyepieces t directly into the star
diagonal.
11. To install one of the included eyepieces (K or L), loosen the
thumbscrew on the star diagonal, then slide the chrome
barrel of the eyepiece into it (refer to Figure 10).Then tighten
the thumbscrew to hold the eyepiece in place.
CONGRATS! The telescope is now fully assembled. Before it
can be effectively used, however, there are a couple of things
to do to prepare the telescope for operation.
III. Preparing the Telescope
for Operation
The 2" rack-and-pinion focuser of the AstroView 102mm EQ
Refractor comes with a removable 1.25” step-down adapter
installed (see Figure 10).This adapter allows use of the included
1.25" star diagonal and 1.25” eyepieces. Alternatively, one can
also use an optional 2” diagonal and 2” eyepieces if so desired,
simply by removing the 1.25” adapter (Figure 11). Doing so
exposes the 2" accessory collar into which the optional 2" diago-
nal’s barrel would be inserted. Some 2" eyepieces can have a
wider apparent eld of view than corresponding 1.25" eyepieces,
and can have a larger eye lens. But 2" eyepieces are typically
more expensive.
Aligning and Using the EZ Finder II Reflex Sight
The EZ Finder II (Figure 12) works by projecting a tiny red dot
(it’s not a laser beam) onto a tinted lens mounted in the front of
the unit.When you look through the EZ Finder II, the red dot will
appear to oat in space, helping you locate your target object.
The red dot is produced by a light-emitting diode (LED) near the
rear of the sight. One 3-volt lithium battery provides the power
for the diode.
In order to power the EZ Finder II for the rst time, you must rst
remove the tab sticking out from the battery compartment. Just
pull the tab out with your ngers, then discard it.
Now turn the power knob (see Figure 12) clockwise until you
hear the “click” indicating that power has been turned on. Look
through the back of the reex 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 dim. The intensity of the dot is adjusted by turn-
ing the power knob. For best results when stargazing, use the

4
dimmest possible setting that allows you to see the dot without
difficulty.Typically a dimmer setting is used under dark skies and
a bright setting is used under light-polluted skies or daylight.
At the end of your observing session, be sure to turn the power
knob counterclockwise until it clicks off. When the white dots
on the EZ Finder II’s body and power knob are lined up, the EZ
Finder II is turned off.
Aligning the EZ Finder II
When the EZ Finder II is properly aligned with the telescope,
an object that is centered on the EZ Finder II’s red dot should
also appear in the center of the eld of view of the telescope’s
eyepiece. Alignment of the EZ Finder II is easiest to do during
daylight, before observing at night.
Aim the telescope at a distant object such as a telephone pole
or roof chimney and center it in the telescope’s eyepiece. The
object should be at least 1/4 mile away. Now, with the EZ Finder
II turned on, look though the EZ Finder II. The object should
appear somewhere in the eld of view.Without moving the main
telescope, use the EZ Finder II’s azimuth (left/right) and altitude
(up/down) adjust-ment knobs (see Figure 12) 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’s eld of view. If it is not, recenter 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.
Once aligned, EZ Finder II will usually hold its alignment even
after being removed and then re-installed in the dovetail base.
Otherwise, only minimal realignment will be needed.
Balancing the telescope
To insure smooth movement of the telescope on both axes of
the equatorial mount, it is imperative that the optical tube be
properly balanced. First we’ll balance the telescope with respect
to the R.A. axis, then the Dec. axis.
1. While keeping one hand on the telescope optical tube (sold
separately), loosen the R.A. lock knob (see Figure 13A).
Make sure the Dec. lock knob is locked, for now. The tele-
scope should now be able to rotate freely about the R.A.
axis. Rotate it until the counterweight shaft is parallel to the
ground (i.e., horizontal), as in Figure 13A.
2. Now loosen the counterweight lock knob and slide the weight
along the shaft until it exactly counterbalances the telescope.
That’s the point at which the shaft remains horizontal even
when you let go of the telescope with both hands.
3. Retighten the counterweight lock knob.The telescope is now
balanced on the R.A. axis.
4. To balance the telescope on the Dec. axis, rst tighten the
R.A. lock knob, with the counterweight shaft still in the hori-
zontal position.
5.With one hand on the telescope optical tube, loosen the Dec.
lock knob (see Figure 13B). The telescope should now be
able to rotate freely about the Dec. axis. If the front of the
telescope swings downward, that means you need to move
it back in the mount’s saddle. If the front of the telescope
swings upward, then you need to shift the telescope forward
in the saddle. To move the telescope in the saddle, loosen
the saddle lock knobs just a little – so the dovetail bar doesn’t
accidentally pop out of the saddle. Position the telescope
so it remains horizontal when you carefully let go with both
hands.This is the balance point.
6. Retighten the saddle clamp knobs.
The telescope is now balanced on both axes. Now when you
loosen the lock knob on one or both axes and manually point
the telescope, it should move without resistance and should not
drift from where you point it.
Figure 2. A) Place center of accessory tray over the center of the
leg brace assembly. B) Press down and twist tray until the tabs click
under retaining clips.
Tray tab
Retaining
clip
A. B.
Figure 3. Secure the EQ mount to the tripod with the mount
attachment knob.
Latitude
adjustment
T-bolt
Mount
attachment
knob
Latitude
adjustment
T-bolt
(need to
install)
(pre-
installed)

5
IV. Understanding and
Using the Equatorial Mount
When you look at the night sky, you no doubt have noticed the
stars appear to move slowly from east to west over time. That
apparent motion is caused by the Earth’s rotation (from west to
east). An equatorial mount is designed to compensate for that
motion, allowing you to easily “track” the movement of astro-
nomical objects, thereby keeping them from drifting out of the
telescope’s eld of view while you’re observing.
This is accomplished by slowly rotating the telescope on its right
ascension (R.A.) axis, using only the R.A. slow-motion cable.
But rst the R.A. axis of the mount must be aligned with the
Earth’s rotational (polar) axis—a process called polar alignment.
Polar Alignment
For Northern Hemisphere observers, approximate polar align-
ment is achieved by pointing the mount’s right ascension axis
at the North Star, also known as Polaris (see Figures 6 and
14). It lies within 1° of the north celestial pole (NCP), which is
an extension of the Earth’s rotational axis out into space. Stars
in the Northern Hemisphere appear to revolve around the NCP.
To nd Polaris in the sky, look north and locate the pattern of the
Big Dipper (Figure 14).The two stars at the end of the “bowl” of
the Big Dipper point approximately to Polaris.
Observers in the Southern Hemisphere aren’t so fortunate to
have a bright star so near the south celestial pole (SCP). The
star Sigma Octantis lies about 1° from the SCP, but it is barely
visible with the naked eye (magnitude 5.5).
To polar align the equatorial mount:
1. Roughly level the mount by adjusting the length of the three
tripod legs as needed.
2. Loosen the latitude lock knob a half turn or so (Figure 15).
3. Using the two latitude adjustment T-bolts, set the latitude so
that the pointer on the latitude scale indicates the latitude
of your observing location. (Loosen one latitude adjustment
T-bolt before tightening the other.) If you don’t know your
location’s latitude, you can look it up on the internet. For
example, if your latitude is 35° North, set the pointer to 35.
Then retighten the latitude lock knob. The latitude setting
Figure 4. A) Thread the counterweight shaft onto the mount.
B) After removing the safety stop, slide the counterweight onto the
shaft.
A. B.
Safety stop
Figure 5. Attach the two slow-motion cables to the mount.
Slow motion
cable
Figure 6. The assembled EQ-13 mount looks like this.
Dec. slow-motion
cable
R.A. slow-motion
cable
Saddle
clamp
knobs
Dec. lock knob
R.A. lock knob
Dovetail
saddle
R. A. (Polar) axis
Dec. axis
To Polaris

6
Figure 7. Install the optical tube on the mount by placing the
dovetail bar into the saddle, then secure it by tightening the two
saddle clamp knobs.
Figure 8. Attach the EZ Finder II by sliding the bracket it into the
dovetail shoe as shown, then secure it with the thumbscrew on the
shoe.
Figure 9. Insert the chrome barrel of the star diagonal into
the 1.25" adapter’s accessory collar, then secure it with the two
thumbscrews.
Dovetail
Mounting bar
Saddle
Sight tube
1.25"
accessory
collar
Saddle
clamp
knobs
should not have to be adjusted again unless you move to a
different viewing location some distance away.
4. Next, loosen the mount attachment knob (see Figure 15)
just enough to allow you to rotate the mount in azimuth.Then
rotate the mount by hand so the R.A. axis points roughly at
Polaris (see Figure 6). If you cannot see Polaris directly from
your observing site, consult a compass and rotate the mount
so the telescope points North. Then retighten the mount
attachment knob.
The equatorial mount is now (roughly) polar aligned. From
this point on in your observing session, you should not
make any further adjustments to the azimuth or the latitude
of the mount, nor should you move the tripod. Doing so will
ruin the polar alignment.The telescope should henceforth
be moved only about its R.A. and Dec. axes.
Using the R.A. and Dec. Slow-Motion ControlCables
The R.A. and Dec. slow-motion control cables (see Figure 6)
allow ne adjustment of the mount’s position to center objects
within the telescope’s eld of view. Before using the cables,
manually “slew” the mount to point the telescope in the vicin-
ity of the desired target. Do this by loosening the R.A. and Dec.
lock knobs and moving the telescope about the mount’s R.A.
and Dec. axes. Once the telescope is pointed somewhere close
to the object to be viewed, retighten the mount’s R.A. and Dec.
lock knobs.
The object should now be visible somewhere in the eld of view
of the telescope’s nder scope of reex sight. If it isn’t, use the
slow-motion controls to scan the surrounding area of sky. Note:
when using the slow motion cables, the R.A. and Dec lock
knobs should be tightened, not loose. When the object is
visible in the EZ Finder II, use the slow-motion controls to center
it. Now, look in the telescope’s eyepiece and use the slow-motion
controls to center it in the eyepiece.
The R.A. slow motion cable can turn the mount’s R.A. axis a full
360 degrees. However, the Dec. slow-motion cable has a limited
range of about 25 degrees. If you reach the end of the range

7
Figure 10. Insert the eyepiece into the star diagonal and secure
it with the thumbscrew.
Figure 11. The 1.25" adapter can be removed from the 2"
focuser, allowing use of an optional 2" diagonal and 2" eyepieces if
desired.
2"
accessory
collar
2" accessory
collar
1.25"
adapter
1.25"
adapter
Star
diagonal
Eyepiece
Drawtube
tension
thumbscrew
1.25" collar
Focus
wheel
of motion – and you cannot turn the knob further – you should
reverse direction by 10 degrees or so, then release the Dec. lock
knob and move the telescope by hand back to about where it
was pointed before the slow-motion cable stopped turning. Now
you should be able to use the slow motion cable again for ne
pointing in either direction.
Tracking Celestial Objects
When you observe a celestial object through the telescope,
you’ll see it drift slowly across the eld of view. To keep it in the
eld, assuming the equatorial mount is polar aligned, just turn
the R.A. slow-motion control cable counterclockwise to track.
The Dec. slow-motion control cable is not needed for tracking.
Objects will appear to move faster at higher magnications,
because the eld of view is narrower.
Optional Electronic Drive for Automatic Tracking
An optional DC electronic drive is available for the AstroView
102 EQ Refractor’s equatorial mount. This battery-operated
drive provides automated, hands-free tracking. Objects will then
remain stationary in the eld of view without any manual adjust-
ment of the R.A. slow-motion control cable.
Understanding the Setting Circles
The two setting circles on an equatorial mount enable you to
locate celestial objects by their “celestial coordinates”. Every
object resides in a specic location on the “celestial sphere”.That
location is denoted by two numbers: its right ascension (R.A.)
and declination (Dec.). In the same way, every location on Earth
can be described by its longitude and latitude. R.A. is similar to
longitude on Earth, and Dec. is similar to latitude.The R.A. and
Dec. values for celestial objects can be found in any star atlas
or online planetarium app.
On the AstroView 102 EQ Refractor’s equatorial mount, the R.A.
setting circle is scaled in hours, from 1 through 24, with small
marks in between representing 10-minute increments (Figure
16).The numbers at the base of the setting circle scale apply to
the Northern Hemisphere while the numbers above them apply
to viewing in the Southern Hemisphere.
The Dec. setting circle is denoted in degrees, with each main
mark representing 10° increments (Figure 16). Values of Dec.
coordinates range from +90° to -90°. The 0° mark indicates
the celestial equator. For this mount, the number scale goes to
90 on either side of 0 – there are no (+) or (-) signs. When the
telescope is pointed north of the equator, actual values of Dec.
are negative.
For example, the coordinates for the Orion Nebula (M42) are:
R.A. 5h 35.4m Dec. -5° 27'
Power switch
Red LED
Battery cover
Ta b
Altitude
adjustment
knob
Azimuth
adjustment
knob
Figure 12. Features of the EZ Finder II.

8
That’s 5 hours and 35.4 minutes in right ascension, and -5
degrees and 27 arc-minutes in declination (there are 60 arc-
minutes in 1 degree of declination).
Before you can use the setting circles to locate objects, the
mount must be polar aligned, and the setting circles must be
calibrated. The easiest way to calibrate the setting circles is to
point the telescope at an identiable bright star, center it in the
eyepiece, then set the setting circles to the star’s published
coordinates, which you can nd in a star atlas or astronomical
software program, or perhaps on the internet.
Calibrating the Right Ascension Setting Circle
1. Identify a bright star near the celestial equator (Dec. = 0°)
and look up its coordinates in a star atlas.
2. Loosen the R.A. and Dec. lock knobs on the equatorial
mount, so the telescope optical tube can move freely.
3. Point the telescope at the bright star near the celestial equa-
tor whose coordinates you know. Lock the R.A. and Dec. lock
knobs. Center the star in the telescope’s eld of view with the
slow-motion control cables.
4. Loosen the thumb screw located just above the R.A. setting
circle pointer; this will allow the setting circle to rotate freely.
Rotate the setting circle until the pointer indicates the R.A.
coordinate listed in the star atlas for the object. Retighten the
thumb screw.
Calibrating the Setting Circles
Using a star atlas or astronomy planetarium program, identify
a bright star visible in your sky. Some smartphone astronomy
apps allow you to hold your phone up to the sky and the app
will identify the stars and constellations visible in the direction
you’re pointing to. Note the right ascension and declination coor-
dinates of the star.
Let’s take as an example Altair, in the constellation Aquila. Its
coordinates are:
R.A. 19 hr 51 min, Dec 8° 52'
1. Loosen the R.A. and Dec. lock knobs on the equatorial
mount, so the telescope optical tube can move freely.
2. Point the telescope at Altair. Lock the R.A. and Dec. lock
knobs. Center the star in the eyepiece with the slow-motion
control cables.
3. Rotate the R.A. setting circle until the metal pointer indicates
19 hr 51 min.
4. Then rotate the Dec. setting circle until the metal pointer
indicates +8° 52'
Figure 13. A) Balance a telescope in right ascension by sliding the counterweight along the shaft until it counterbalances the telescope.
B) Balance the telescope on the declination axis by sliding the dovetail mounting bar forward or back in the mount’s saddle.
A. B.
R.A. lock knob
Saddle
clamp
knobs
Counterweight lock
knob
Counterweight
shaft
Dec. lock knob

9
Note that the setting circles may be a little hard to rotate.
But just grab it rmly around the edge and twist it and it
will rotate.
Finding Objects with the Setting Circles
Now that both setting circles are calibrated, look up the coordi-
nates of an object you wish to view.
1. Loosen the R.A. lock knob and rotate the telescope until
the R.A. value from the star atlas matches the reading on
the R.A. setting circle. Remember to use the lower set of
numbers on the R.A. setting circle if you’re in the Northern
hemisphere. Retighten the lock knob.
2. Loosen the Dec. lock knob and rotate the telescope until the
Dec. value from the star atlas matches the reading on the
Dec. setting circle. Remember that values of the Dec. setting
circle are positive when the telescope is pointing north of the
celestial equator (Dec. = 0°), and negative when the tele-
scope is pointing south of the celestial equator. Retighten
the lock knob.
Most setting circles are not accurate enough to put an object
dead-center in the telescope’s eyepiece, but they should place
the object somewhere within or near the eld of view of the
nder scope, assuming the equatorial mount is accurately polar
aligned. Use the slow-motion controls to center the object in the
nder scope, and it should appear in the telescope’s eld of view.
The R.A. setting circle must be re-calibrated every time you wish
to locate a new object. Do so by calibrating the setting circle for
the centered object before moving on to the next one.
Choosing an Observing Site
When selecting a location for observing, get as far away as
possible from direct articial light such as streetlights, porch
lights, and automobile headlights. The glare from these lights
will greatly impair your dark-adapted night vision. Set up on a
grass or dirt surface, not asphalt, because asphalt radiates
Figure 14. To nd Polaris in the night sky, look north and nd the
Big Dipper. Extend an imaginary line from the two "Pointer Stars" in
the bowl of the Big Dipper. Go about ve times the distance between
those stars and you'll reach Polaris, which lies within 1° of the north
celestial pole (NCP).
Big Dipper
(in Ursa Major)
Little Dipper
(in Ursa Minor)
Cassiopeia
N.C.P.
Pointer
Stars
Polaris
Figure 15. Loosen the latitude lock knob, then use the two
latitude adjustment T-bolts to set the latitude scale pointer to your
location’s latitude.
Figure 16. The R.A. and Dec. setting circles allow you to locate
objects by their R.A. and Dec. coordinates.
Latitude scale
Pointer
RA setting
circle
Pointer
Dec. setting
circle
Mount attachment knob
Latitude lock
knob
Latitude
adjustment
T-bolts

10
more heat. Heat disturbs the surrounding air and degrades the
images seen through the telescope. Avoid viewing over roof-
tops and chimneys, as they often have warm air currents rising
from them. Similarly, avoid observing from indoors through an
open (or closed) window, because the temperature difference
between the indoor and outdoor air will cause image blurring
and distortion.
If at all possible, escape the light-polluted city sky and head for
darker country skies.You’ll be amazed at how many more stars
and deep-sky objects are visible in a dark sky!
Confused About Pointing the Telescope?
Beginners occasionally experience some confusion about how
to point the telescope overhead or in other directions. One thing
you DO NOT do is make any adjustment to the mount’s latitude
setting or to its azimuth position. That will throw off the mount’s
polar alignment. Once the mount is polar aligned, the telescope
should be moved only about the R.A. and Dec. axes.This is done
by loosening one or both of the R.A. and Dec. lock knobs and
moving the telescope by hand, or keeping the knobs tightened
and moving the telescope using the slow-motion cables.
V. Astronomical Observing
For many, this will be your rst foray into the exciting world of
amateur astronomy. The following information and observing
tips will help get you started.
Choosing an Observing Site
When selecting a location for observing, get as far away as
possible from direct articial light such as street lights, porch
lights, and automobile headlights. The glare from these lights
will greatly impair your dark-adapted night vision. Set up on a
grass or dirt surface, not asphalt, because asphalt radiates
more heat. Heat disturbs the surrounding air and degrades the
images seen through the telescope. Avoid viewing over roof-
tops and chimneys, as they often have warm air currents rising
from them. Similarly, avoid observing from indoors through an
open (or closed) window, because the temperature difference
between the indoor and outdoor air will cause image blurring
and distortion.
If at all possible, escape the light-polluted city sky and head for
darker country skies.You’ll be amazed at how many more stars
and deep-sky objects are visible in a dark sky!
“Seeing” and Transparency
Atmospheric conditions vary signicantly from night to night.
“Seeing” refers to the steadiness of the Earth’s atmosphere at
a given time. In conditions of poor seeing, atmospheric turbu-
lence causes objects viewed through the telescope to “boil.” If
you look up at the sky and stars are twinkling noticeably, the
seeing is poor and you will be limited to viewing at lower magni-
cations.At higher magnications, images will not focus clearly.
Fine details on the planets and Moon will likely not be visible.
In conditions of good seeing, star twinkling is minimal and
images appear steady in the eyepiece. Seeing is best over-
head, worst at the horizon. Also, seeing generally gets better
after midnight, when much of the heat absorbed by the Earth
during the day has radiated off into space.
Especially important for observing faint objects is good “trans-
parency”—air free of moisture, smoke, and dust.All tend to scat-
ter light, which reduces an object’s brightness.Transparency is
judged by the magnitude of the faintest stars you can see with
the unaided eye (5th or 6th magnitude is desirable).
Cooling the Telescope
All optical instruments need time to reach “thermal equilib-
rium.” The bigger the instrument and the larger the temperature
change, the more time is needed. Allow at least 30 minutes for
your telescope to acclimate to the temperature outdoors before
you start observing with it.
Let Your Eyes Dark-Adapt
Don’t expect to go from a lighted house into the darkness of the
outdoors at night and immediately see faint nebulas, galaxies,
and star clusters—or even very many stars, for that matter.Your
eyes take about 30 minutes to reach perhaps 80% of their full
dark-adapted sensitivity. As your eyes become dark-adapted,
more stars will glimmer into view and you’ll be able to see fainter
details in objects you view in your telescope.
To see what you’re doing in the darkness, use a red-ltered
ashlight rather than a white light. Red light does not spoil your
eyes’ dark adaptation like white light does.A ashlight with a red
LED light is ideal. Beware, too, that nearby porch, streetlights,
and car headlights will ruin your night vision.
Figure 17. To change the battery, A) Pry the battery cover off
by inserting a small at-head screwdriver into the slot. B) Insert
a CR3023 battery under the retaining clip, with positive “+” side
facing the retaining clip. Then re-attach the battery cover.
Slot
Retaining
clip
"+" side
of battery
A
B