Ealing data
 Observatory location for planetarium software
 Fully (100%) illuminated circle
 Latitude – 40°38’40” N | 40.644° N
 Linear diameter _____ mm
 Longitude - 112°18’8” W | 112.3022° W
 TFOV angular diameter _______ arcmin
 Altitude – 4252 feet | 1296 meters
 Diffraction free image size per Sinnott’s equation
 Objective diameter – ~16” | 400mm
 36mm or 72% of a 2” barrel
 Obstructed diameter – 152.4 mm 38%
 (Sky & Telescope May, 1991:528-531 at 531.
W = 0.0007 * F^3 )
 Contrast effective aperature ( D_eff = D_obj –
d_obstructed) - 248 mm
 Light grasp effective aperatrue ( D_lg = sqrt (
D_obj^2 – d_obstructed^2 ) ) - 313 mm
 Focal length – 200” | 5080mm
 F ratio – 12.7
 Prime focus distance
Back of focuser tube housing to prime focus ~
34cm, including 2” right angle (2/27/2005)
Back of focuser tube housing to back of right
angle 26cm (2/27/2005)
 TFOV 1/3° (1200”) 168x with standard eyepiece –
odd # of reflections.
 Maksutov 5” finder - FOV 1° with 40mm lens – even
# reflections
 70mm refractor finder - FOV 3.3° - odd #
reflections - similar to a binocular view in scale
 Telrad finder - three circles - ½↑, 2° and 4°.
 Digital setting circles– Orion Skywizard
Obtain manual at
http://www.telescope.com/text/content/pdf
/inst_07803.pdf
Best seeing is the 30° diameter circle surrounding the zenith
Zenith
Meridian
08 00 LST
02 00 RA
14 00 RA
Looking south
A typical three hour observing session covers two these 30° diameter circles
Eastern 30° zone and its stars
drift into zenithal good seeing
position later in the evening.
West-most star in good
seeing zone observed at
start of session.
Zenith
Meridian
08 00 LST
West 02 00 RA
East 14 00 RA
Looking south
Observation planning can help minimize meridian swaps
• Working west to east within a night’s drift zone minimizes scope travel and meridian swaps.
Relationship of meridian swap, local sidereal time and target right ascension (RA)
• Local sidereal time measures the position of the meridian on your star charts.
• On the observing night, keep an extra watch set to local sidereal time (LST). Obtain LST from << http://tycho.usno.navy.mil/sidereal.html >>
• A meridian swap will be needed if:
• RA current target > Local sidereal time > RA Desired target - or
• RA current target < Local sidereal time < RA Desired target
• A meridian swap is not needed if:
• RA current target & RA Desired target > Local sidereal time - or
• RA current target & RA Desired target < Local sidereal time
Zenith
Meridian
10 00 RA
08 00 LST
03 30 RA
13 00 RA
14 00 RA
02 00 RA
Looking south
Right angle slewing – Initial rough RA slew to target vicinity
 Minimize meridian swaps and potential off turning tube to
lower than horizontal by only using the RA rough slew
 Slew in right ascension to bright star on same RA as
target.
 Slew in declination to vicinity of target.
Do not use the
declination rough
slew route
5h
6h
M37
30°
Aldebaran
10°
 Avoid using the Declination rough slew
route. Declination rough slew route can
turn tube to lower than horizontal where
subsequent RA slew crosses the
meridian.
Do use the
RA rough
slew route
Estimate declination
slew at right angles
to declination lines
and not along angled
right ascension lines.
RA rough slewing grab points | RA and Dec
clutches
Right ascension
clutch
Grab points for
right ascension
slewing
Declination
clutch
Meridian looking south
Declination rough slewing grab points
Slewing arm
Meridian looking south
The declination clutch housing can be used as a pointer during the initial
rough slew
When slewing in right ascension, use declination
clutch housing as pointer sight to rough align
target in right ascension.
Then use the Telrad mounted on the housing to
navigate the scope to your waypoint bright star. A
Telrad finder has three circles - ½↑, 2° and 4°.
Meridian looking south
Right angle slewing – Medium slews to target
 Medium slews are 2°-8° in either RA or declination. On chart,
measure travel to target in eyepiece True Field of Views (TFOVs)
 The slew controller speed is too slow to use for medium
slewing.
Eyepiece
TFOV
Medium slew
distance
Either route
is okay for
fine slewing
Slewing arm
 Medium slewing is best done by ignoring the reversed
eyepiece view for a moment. Look over the top of the scope
frame with the naked eye, and holding the slew arm, practice
which motion in RA or declination will take you to the target.
 Then look in the eyepiece and ignoring the direction of travel
of the TFOV, move your arm in the proper direction, counting off
the eyepiece TFOVs. Visualize the direct view movement of the
scope as you get closer to the target.
Right angle slewing – Finding during the medium slew
 Two finders suitable for medium
slewing are the –
Maksutov 5” FOV 1° with 40mm
lens – even # reflections – similar to
a small refractor view,

 70mm refractor FOV 3.3° - odd #
reflections – similar to a binocular
view.
 Don’t discount the 70mm finder. It is
similar to a binocular view. Familiarizing
yourself with the asterisms in the 2-3°
star field leading to your target with
binoculars prior to your Ealing session
can translate into a quick find during the
session using the 3° 70mm finder.
Position of the
main finders
mounted on the
telescope.
Meridian looking south
Right angle slewing – Fine tune slews to target
 Reserve final fine tune slew for last 1°. The slew controller
speed is too slow to use for medium slewing 2°-4°.
 Fine slew using either the RA route or declination route
Final fine slew
distance
Eyepiece
TFOV
 Use slew controller for slow travel
Wide buttons – Declination
Narrow buttons – Right ascension
Either route
is okay for
fine slewing
Park position
But tube remains above
horizontal on the east
side of the bay.
Dec park
position
marker
Only time when
weight rises
above horizontal
RA park
position
marker
Meridian
looking
south
Meridian
looking
north
Park position – check the declination park markings from a distance
When moving to declination
park and looking up at the
marks from below, the
perspective effect can make the
parking marks appear to be
aligned, when if fact they are
not.
Step back two or three feet
from the scope and recheck
that the declination parking
marks are aligned.
Other use notes
 When exiting building, set combination lock to “555.”
 Safe position of the rolling ladder during telescope slewing is by the north east
corner of the room, short-ladder side next to the north east door.
 Rolling ladder is unlocked with a foot pedal/bar below the first step. Standing on
the first step triggers the anti-roll lock.
 Red wall lights should be kept at ½ power to prevent the lights from overheating
the red glass covers. If overheated, the glass covers will fracture.
 An astrophotography camera holder is available. The square weights can be
removed to keep the telescope balanced. Square weights equal to the camera’s
weight are removed, otherwise the scope will be unbalanced and will fall when the
declination clutch is loosened.

An aperature mask is stored behind the drive power console.

Aligning finders
 The Maksutov finder can be aligned to scope by “strong-arming” it into
position. This finder is mounted on friction disks.
 The other finder scopes have three screw rings for finder aligning.
Other use notes -2
 Open rolling roof after Sun is low enough that direct rays do not strike the scope or
observatory.
 Chock for rolling roof is stored behind roller.
 Tie-down for rolling roof is stored by leaving it dangle vertically in the corner.
 The tie-down is released by pushing the tab button in the center of tie-down lock
mechanism.
 The Skywizard moves between modes with the up and down arrow keys.
A naked-eye limited magnitude chart for the SPOC site
 Due to light pollution in the eastern sky of the site, an light pollution reduction (LPR) broadband
filter is recommended for east and south deep sky object viewing.
 A limiting magnitude chart for the SPOC site made ______________:
N
NE
NW
W
E
SE
SW
S
NELM values determined using some of the 26 IMO limiting magnitude fields for the northern sky.
See << http://obs.nineplanets.org/lm/rjm.html >> and <<
http://www.imo.net/visual/major01.html#table2 >>.