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Izar and Porrima

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#1 Kon Dealer

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Posted 06 April 2013 - 06:13 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?

#2 Rich (RLTYS)

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Posted 06 April 2013 - 06:41 AM

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

Rich (RLTYS)

#3 Bonco

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Posted 06 April 2013 - 03:11 PM

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

#4 CelestronDaddy

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Posted 06 April 2013 - 03:17 PM

Good report and description... Tony

#5 Rich (RLTYS)

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Posted 07 April 2013 - 06:54 AM

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

Rich (RLTYS)

#6 Rutilus

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Posted 07 April 2013 - 07:12 AM

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

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#7 ziridava

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Posted 07 April 2013 - 07:29 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

#8 brianb11213

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Posted 07 April 2013 - 08:11 AM

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.

#9 ziridava

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Posted 07 April 2013 - 09:09 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.

#10 Kon Dealer

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Posted 07 April 2013 - 12:32 PM

What's the current separation of Porrima?

#11 Rutilus

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Posted 07 April 2013 - 12:34 PM

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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#12 brianb11213

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Posted 07 April 2013 - 01:33 PM

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.

#13 Bonco

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Posted 07 April 2013 - 05:12 PM

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

#14 WRAK

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Posted 08 April 2013 - 04:22 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

#15 ziridava

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Posted 10 April 2013 - 01:50 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

#16 cildastun

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Posted 10 April 2013 - 02:14 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

#17 buddyjesus

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Posted 10 April 2013 - 08:48 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

#18 ziridava

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Posted 11 April 2013 - 03:13 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

#19 fred1871

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Posted 11 April 2013 - 08:13 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.



#20 Bonco

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Posted 11 April 2013 - 08:39 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

#21 azure1961p

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Posted 11 April 2013 - 10:45 PM

Agreed. However if indeed the scope had been a 24mm aperture, Fred's points would stand well of course.

Pete

#22 fred1871

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Posted 12 April 2013 - 01:19 AM

I thought it was a reference to a galileo scope, such as I've seen some folk experimenting with - rather than a single-lens eyepiece. William Herschel used such single-element eyepieces at times, though that's rare in post-Huyghens observing. Ok, so it's an eyepiece. I shall simply express myself puzzled about combining a later type of telescope with a primitive eyepiece. Which I think is why I misread the note.

Question suggested by my earlier ramble - what's the smallest aperture that anyone's seen Izar split with? We know that 60mm does it, and Buffham with ~48mm. The latter (1.875" aperture, unobstructed) has a Dawes Limit of ~2.4", which suggests it might be near the best possible. Of course, "resolved" as we've often discussed here can mean anything from separated by a black space to vaguely elongated. Any offers of splits need to spell that out. :grin:

#23 ziridava

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Posted 12 April 2013 - 04:15 PM

Please accept my apologies I was unclear and I created confusion.
I was just using a Galilean ocular of 24mm focus at full aperture of my 125mm Newtonian.
I cannot reach focus with Galilean eyepieces without using a Barlow lens.For now I have and sometime use three Galilean oculars of 27mm ,24mm and 18 mm focus.
I like to use them in a sort of reenactment.
Galilean eyepieces were used until the end of XIX Century.
The last famous person to use them was Thomas Grubb.
Apart of historical flavor,they are optically very good.
A good Galilean ocular is able to compete with an orthoscopic.

Off-topic:I start thinking on this forum there are mind-reading people :)
Once it was unveiled,I have to recognise:it is true,I'm on my way building a Galilean refractor ,this week I made some progress on it.This was supposed to be for a while a ''secret project'' ,meant to be a tribute to the memory of Giovanni Hodierna,a reenactment of his observations.

Mircea

#24 Bonco

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Posted 12 April 2013 - 06:16 PM

I thought it was a reference to a galileo scope, such as I've seen some folk experimenting with - rather than a single-lens eyepiece. William Herschel used such single-element eyepieces at times, though that's rare in post-Huyghens observing. Ok, so it's an eyepiece. I shall simply express myself puzzled about combining a later type of telescope with a primitive eyepiece. Which I think is why I misread the note.

Question suggested by my earlier ramble - what's the smallest aperture that anyone's seen Izar split with? We know that 60mm does it, and Buffham with ~48mm. The latter (1.875" aperture, unobstructed) has a Dawes Limit of ~2.4", which suggests it might be near the best possible. Of course, "resolved" as we've often discussed here can mean anything from separated by a black space to vaguely elongated. Any offers of splits need to spell that out. :grin:

Fred,
60mm/900mm telescope with 7mm .965 eyepiece = 128X. Izar perfectly resolved with dark space between the stars. 6mm resolved it too but better viewed with the 7mm.
Bill

#25 ziridava

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Posted 21 April 2013 - 10:48 AM

Soon I will be able to compare directly my 9mm Vixen orthoscopic to a brand new Galilean eyepiece of 9mm focus.

Coming back to double star observation,last night myself,with my 125mm F7 Dobsonian/ and my friend Emil with his 114mm F8.8 Bird-Jones Newtonian, were in front of the City Hall for a public star party as part of ISAN 6.

It was a nice surprise to be able to split Porrima and especially Izar at 140x/Faworski 10mm Plossl+1,8x Barlow in my 125mm Dobsonian,from that litle corner of Hell.
The complete list of stars on the double/multiple star menu of our ISAN 6 Star-Party were Alcor-Mizar,Castor,Porrima and Izar.
The light polution there is huge:only the Moon,Jupiter,Saturn were visible.I had to guess where to look for Porrima, Izar or Mizar.
After a while,by blind guessing ,I found also M44.
About 120-150 people had their first telescopic view of some heavenly bodies,including some very fine double stars.

Mircea






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