[bigjoe (JOSEPH)]

Hello fellow IISers..

No its not Tennis.

Eugene(Bombardon) and myself(bigjoe) have come up with the idea of a Monthly Constellation Doubles observing report.

We'll tommorrow post the Doubles selected in the Constellation to be observed for that month...giving you plenty of time to observe and report due to weather.

We though we'd choose 6 of the many doubles in ORION to kick it off.

Suggestions for these Monthly Constellation doubles reports, selections etc are also welcome ..esp from Tinderboxsky(Steve) Mekon(John) , Steffen etc.

Though nothing too technical, such as stating position angles as mandatory...as this is for the uninitiated also.....So how to best go about it..PICK some say MAX of 6 Doubles per Constellation..and not always the obvious ones .

This will be for anyone interested in Starsplitting as part of their observing regime...Novice or Veteran.

Even if your not an avid doubles observer, we would like to hear of your observation .....even if you only get time to observe just one of those selected in your humble 60mm Tasco, let us know!

Resolution limits for your aperture, use either...

The DAWES LIMIT for YOUR scope ..116/Diameter in mm..barely will you see a hairline split.

RAYLEIGHS LIMIT 138/D mm a clear dark line will separate them in comparison.

These LIMITS ALL are based on components of equal magnitude; in practise most doubles are NOT Equal, and tougher.


Tell us about how HARD or EASY it was in your scope, at its RESOLUTION LIMIT e.g. Say 1.1 " in a 4 inch, in as good as seeing as you can..don't worry too much about transperancy..its really the seeing thats important... WHAT WHERE THE ...

Stars selected and observed..state their mags and separations when reporting.


Scope and Eyepiece(s) used .

Magnification(s) used.

Colour Contrasts seen .

SEEING ,Transperancy at the time.

LOCATION, Time, Altitude above horizon(can estimate).

Separation will be given, but is it as stated?.. this for the experienced ones.

PA... Is PA stated accurate..though this is NOT necessary, only for the expert .

Type of doubles observations....you'll need very good seeing at least for the first three.

1: Was it a figure eight..unsplit
2: Kissing and unsplit
3: A hairline split = split
4: Or best, a solid split .

Some doubles will be tough, some easy...the point is to have a go at some, and have fun testing your optics at the same time!

And remember no matter how inexpensive your scope, how cheap your Plossls, Kellners are ...we'd like to hear from you...NO Elitism or bagging scopes welcome .

Remember also SMALLER instruments produce LARGER AIRY DISKS at high magnifications, and can actually be BETTER in poorer seeing than LARGER instruments.. this Airy Disk size, or Diffraction Limit for aperture is inversely proportional to the increasing aperture.

Larger scopes...... some with central obstructions, and their resulting SMALLER Airy Disks, bright diffraction rings or spikes can obscure a faint secondary, long cooldowns, thermal currents crossing mirrors, heat plumes off baffles etc... these need more time to cool down.

Try to use 1 eps as a Standard eyepiece IF you want to judge separations..though this is NOT NECESSARY here, VIZ....

Know what say 10" arc looks like in your go to eyepieces for example as in Rigel.

Formula for this..... OCULAR FIELD STOP in mm X 57.3 / FOCAL LENGTH OF SCOPE IN mm.
EG: EP Has field stop* 3 mm, scope 1719 mm focal length

Then thats .. ( 3 x 57.3 )÷ 1719 = 1/10 degree true field of view or 6 mins of arc or 360" IN YOUR EP....So if a Double has a sep of 36" it will be one tenth of the field width of YOUR STANDARD EP, so you'll get an idea of separations and were the secondary will be in your scope!

You really only need a few EPS for this, a locator widefield , Zoom or some higher powers, and optionally a Standard EP for judging separations...all with a Flat Field.

PS: Remember also ...
MOST SCOPES ABOVE 4" ARE SEEING LIMITED AND NOT DIFFRACTION LIMITED most nights of the year...So be patient get a nice comfy chair, and wait for that moment of good seeing ...it will come...you have a month to report!

bigjoe.