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 >>.