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Kon Dealer
professor emeritus


Reged: 01/05/11

Loc: Cambridge UK
Izar and Porrima
      #5781204 - 04/06/13 07:13 AM

Had two good nights observing these two doubles from my light-polluted back garden.
Get good splits on Izar at around x100 and Porrima at x180 with my 4" refractor.
Izar, in particular, is a beautiful sight- a large yellow/orange star next to a small sky blue one.
What do other people see?


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Rich (RLTYS)Moderator
Postmaster
*****

Reged: 12/18/04

Loc: New York (Long Island)
Re: Izar and Porrima new [Re: Kon Dealer]
      #5781231 - 04/06/13 07:41 AM

With my 10" refl at 74x all three stars of Mizar appear bluish white.

Rich (RLTYS)


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Bonco
Post Laureate
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Reged: 04/17/06

Loc: Florida
Re: Izar and Porrima new [Re: Rich (RLTYS)]
      #5782120 - 04/06/13 04:11 PM

Quote:

With my 10" refl at 74x all three stars of Mizar appear bluish white.

Rich (RLTYS)



I think the OP was about Izar in Bootes. His description is spot on. A beautiful colorful double.
Bill


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CelestronDaddy
scholastic sledgehammer
*****

Reged: 08/22/09

Re: Izar and Porrima new [Re: Kon Dealer]
      #5782129 - 04/06/13 04:17 PM

Good report and description... Tony

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Rich (RLTYS)Moderator
Postmaster
*****

Reged: 12/18/04

Loc: New York (Long Island)
Re: Izar and Porrima new [Re: CelestronDaddy]
      #5783239 - 04/07/13 07:54 AM

Your right, my mistake. With my 10" refl I've observed Izar (STF 1877) as Pale yellow and pale blue.

Rich (RLTYS)


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Rutilus
Carpal Tunnel


Reged: 12/17/10

Re: Izar and Porrima new [Re: Rich (RLTYS)]
      #5783264 - 04/07/13 08:12 AM Attachment (59 downloads)

I love Izar, one of my time favourite doubles.
In my refractors I see orange primary with a blue secondary.


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ziridava
super member


Reged: 08/17/12

Loc: Arad,Romania,Eastern Europe
Re: Izar and Porrima new [Re: Rutilus]
      #5783293 - 04/07/13 08:29 AM

I don't remember where but I remember reading that one of our great ancestors,Reverend Webb maybe,was able to split Izar in a 1.5 inch aperture telescope.
I'm very positive about splitting Porrima in my very small reflectors of 72mm F/11 and 76mm F/9.
But about Izar,I had a couple of times the impression I split it in the 76mm F/9 reflector but still not sure.

What is your experience about smallest telescope to split Izar and Porrima,please?

ziridava


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brianb11213
Postmaster
*****

Reged: 02/25/09

Loc: 55.215N 6.554W
Re: Izar and Porrima new [Re: ziridava]
      #5783365 - 04/07/13 09:11 AM

Quote:


What is your experience about smallest telescope to split Izar and Porrima,please?




Izar: Failed with 60mm, not too hard with 80mm.

Burnham's Celestial Handbook says

"generally a difficult object for a 3 inch glass and not exactly easy for beginners even with a 6 inch. T W Webb, however, observed the images clearly seperated with a 2.25 inch achromat, and also states that Buffham resolved the pair with a 9 inch mirror stopped down to 1.875 inches."

Ancient observations are still relevant as there has been no definite change in seperation since discovery though the position angle has increased from 321 deg in 1829 to 338 deg in 1962.

Porrima: the seperation has been increasing rapidly since 2005/6 when the seperation was only about 0.3 arc sec. Last year I found it pretty easy with 110 mm, this year it should be easier still.


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ziridava
super member


Reged: 08/17/12

Loc: Arad,Romania,Eastern Europe
Re: Izar and Porrima new [Re: brianb11213]
      #5783457 - 04/07/13 10:09 AM

Thank you Brian,I believe this is the information I remember.

I agree,Izar was not easy pray neither in my 125mm F/7 Newtonian.The main mirror in that telescope it is small but it has a lambda/24 accuracy according to the Millie-Lacroix test made by my friend Gavril Beches who made it and who was a very skilled mirror grinder.
Until I had a prism acting as a secondary mirror ,I was able to split Izar very rarely.Since I changed to a Chinese mirror secondary,I'm able to split Izar on any clear night when Bootis is above horizon.
I believe Izar will be one of the fire-test objects for my refractor under construction using a Carton 60x1000mm lens.


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Kon Dealer
professor emeritus


Reged: 01/05/11

Loc: Cambridge UK
Re: Izar and Porrima new [Re: ziridava]
      #5783805 - 04/07/13 01:32 PM

What's the current separation of Porrima?

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Rutilus
Carpal Tunnel


Reged: 12/17/10

Re: Izar and Porrima new [Re: ziridava]
      #5783808 - 04/07/13 01:34 PM Attachment (60 downloads)

With my 3 inch refractor the companion sits in the diffraction ring, with your 60mm I suspect the
companion will be visible in the inter space between the Airy disk and diffraction.
Carton lenses are great, I've built a scope based on the 100mm lens and it is a superb double star scope.
I will try my scope with a 60mm aperture mask. Here is a photo of my Carton build.


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brianb11213
Postmaster
*****

Reged: 02/25/09

Loc: 55.215N 6.554W
Re: Izar and Porrima new [Re: Kon Dealer]
      #5783938 - 04/07/13 02:33 PM

Quote:

What's the current separation of Porrima?



The 2013 British Astronomical Association Handbook "Ephemerides of Double Stars", which is kept pretty well up to date with modern measures, has the seperation increasing from 1.95 arc sec at the beginning of 2013 to 2.11 arc sec at the beginning of 2014, with the position angle slowly decreasing from 11.1 deg to 8.4 deg.


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Bonco
Post Laureate
*****

Reged: 04/17/06

Loc: Florida
Re: Izar and Porrima new [Re: ziridava]
      #5784450 - 04/07/13 06:12 PM

Quote:

I don't remember where but I remember reading that one of our great ancestors,Reverend Webb maybe,was able to split Izar in a 1.5 inch aperture telescope.
I'm very positive about splitting Porrima in my very small reflectors of 72mm F/11 and 76mm F/9.
But about Izar,I had a couple of times the impression I split it in the 76mm F/9 reflector but still not sure.

What is your experience about smallest telescope to split Izar and Porrima,please?

ziridava




I've had several 100% positive resolution views of Izar with my 60mm/900. On occasion its been easy, but also sometimes impossible. Same for Delta Cyg which is similar in difficulty.
Bill


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WRAK
Pooh-Bah


Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Izar and Porrima new [Re: Bonco]
      #5786459 - 04/08/13 05:22 PM

I will have to wait for begin of June to see both Izar and Porrima in my field of view. Current separations should according to WDS be 3" resp. 1.7". Both doubles should therefore be resolvable with rather small apertures around 60mm. Ich will check this with the help of an iris diaphragm when times and clear skies come.
Wilfried


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ziridava
super member


Reged: 08/17/12

Loc: Arad,Romania,Eastern Europe
Re: Izar and Porrima new [Re: WRAK]
      #5789544 - 04/10/13 02:50 AM

Monday night I splitted Porrima in the 3 inch Newtonian F/9.2 at 93x/''orange'' Celestron Plossl 7.5 mm.
It was a clean, nice split.
No chance with Izar because of clouds.
Mircea


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cildastun
member


Reged: 08/08/12

Loc: Oxford, UK
Re: Izar and Porrima new [Re: ziridava]
      #5790529 - 04/10/13 03:14 PM

Izar (orange-yellow and blue-green to me) splits nicely in my ED80, but not I've not split Porrima with this easily. Splits nicely in my 5" Mak though.

Chris


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buddyjesus
Carpal Tunnel
*****

Reged: 07/07/10

Loc: Davison, Michigan
Re: Izar and Porrima new [Re: cildastun]
      #5791364 - 04/10/13 09:48 PM

I have issues with the jet stream and low altitude making it where I haven't been able to split Porrima since moving from Colorado. Maybe someday one or the other situation will improve.

Izar a beauty for sure


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ziridava
super member


Reged: 08/17/12

Loc: Arad,Romania,Eastern Europe
Re: Izar and Porrima new [Re: buddyjesus]
      #5792700 - 04/11/13 04:13 PM

Last night,after splitting Zeta Cnc at first view in my 125mm F.7 Dobsonian,I made some more experiments with Galilean oculars.Using a 24mm Galilean and 2x Barlow for 72x magnification,I splitted Algieba,Castor was seen in an eight shape and the companion of Izar was visible as a small sphere glued to the main star.No dark space but both diffraction discs clearly visible.
Good result for the oldest ocular known on planet Earth!
Mircea


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Izar and Porrima new [Re: ziridava]
      #5793274 - 04/11/13 09:13 PM

Mircea, your description of seeing Izar (Epsilon Bootis) as "a small sphere glued to the main star" with "both diffraction discs clearly visible" using 24mm aperture at 72x is a puzzle - first, because the Dawes Limit for a double with 24mm aperture is about 4.8", and this pair is, on recent measures, around 2.9" or 3.0". And it's uneven as well, by 2.2 magnitudes.

Izar is usually seen as needing much more than 24mm - the observation mentioned earlier in this thread, of Buffham resolving (whatever that term indicated) the pair with 1.875-inches (47.6mm, near enough twice your 24mm) is meant as a best case achievement. The separation has changed little if at all over time.

I note that Sissy Haas in her book records her own observation of Epsilon Boo as follows:
60mm, 120x: A brilliant amber-yellow star with a deep blue spur on its edge...

That's what we might expect of the pair with that size telescope at that magnification in good seeing. At 40% of the aperture and 60% of the magnification it's hard to believe it's possible to get a similar view.



Edited by fred1871 (04/12/13 02:24 AM)


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Bonco
Post Laureate
*****

Reged: 04/17/06

Loc: Florida
Re: Izar and Porrima new [Re: fred1871]
      #5793337 - 04/11/13 09:39 PM

Fred, Not a puzzle to me. If I read his email correctly he's using a 125mm f7 telescope with a 24mm eyepiece and a 2X barlow = 72X. I've had perfectly resolved views of Izar with my 60mm/900mm scope and find his observation credible.
Bill


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