Ealing data
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Ealing data
Observatory location for planetarium software
Latitude – 40°38’40” N | 40.644° N
Longitude - 112°18’8” W | 112.3022° W
Altitude – 4252 feet | 1296 meters
Objective diameter – ~16” | 400mm
Obstructed diameter – 152.4 mm 38%
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.
Fully (100%) illuminated circle
Linear diameter _____ mm
TFOV angular diameter _______ arcmin
Diffraction free image size per Sinnott’s equation
36mm or 72% of a 2” barrel
(Sky & Telescope May, 1991:528-531 at 531. W = 0.0007 * F^3 )
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
Meridian 08 00 LST
02 00 RA14 00 RA
Looking south
Zenith
A typical three hour observing session covers two these 30° diameter circles
Meridian 08 00 LST
West 02 00 RAEast 14 00 RA
Looking south
Zenith
West-most star in good seeing zone observed at start of session.
Eastern 30° zone and its stars drift into zenithal good seeing position later in the evening.
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)
Meridian
08 00 LST
02 00 RA
03 30 RA
14 00 RA
10 00 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
Looking south
Zenith
13 00 RA
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.
M37
Estimate declination slew at right angles to declination lines and not along angled right ascension lines.
Aldebaran
5h6h
30°
10°
Do use the RA rough
slew route
Do not use the declination rough slew
route
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.
RA rough slewing grab points | RA and Dec clutches
Meridian looking south
Grab points for right
ascension slewing
Right ascension
clutch
Declination clutch
Declination rough slewing grab points
Meridian looking south
Slewing arm
The declination clutch housing can be used as a pointer during the initial rough slew
Meridian looking south
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°.
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.
Either route is okay for
fine slewing
Eyepiece TFOV
Medium slew distance
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.
Slewing arm
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.
Meridian looking south
Position of the main finders
mounted on the telescope.
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
Use slew controller for slow travel
Wide buttons – Declination
Narrow buttons – Right ascension
Either route is okay for
fine slewing
Eyepiece TFOV
Final fine slew distance
Park position
Meridianlookingsouth
But tube remains above horizontal on the east side of the bay.
Only time when weight rises above horizontal
Meridian looking
north
RA park position marker
Dec park position marker
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
S
WE
SE SW
NWNE
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 >>.