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Izar very difficult to split

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#1 Buqibu

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Posted 29 April 2021 - 12:48 PM

Hi all! This question may have been asked many times, sorry if thats the case. Anyway, I was looking at Izar yesterday and honestly couldn't make out that it was a double. I found it odd, because everywhere online it says it is a very brilliant visual binary. So I look to see if the scope was the limiting factor here, I have a 4 inch, 660mm achro. However I saw some comments of people saying they could split it even with 70mm scopes. I tried 33x, 66x and 132x. The only time I can say I saw something resembeling a second companion was in the 66x. But I think that was just my imagination working with the chromatic aberration, because the "companion" I saw wasn't where it's supposed to be. Seeing was also good as far as I could tell, I could easily split Mizar for example. Wondering if its the achro, the light pollution (I live in bortle 6ish maybe 7 skies) or the potential poor seing (although this last one seems unlikely). Thanks in advance! If I simply can't split it with my current setup, could you recommend some nice, easy doubles I can see? I've already seen Almach, Mizar, Achird, Cor Caroli etc... I've heard Albiero is very nice, any others? Thanks in advance and sorry for the long post.

#2 Astrojensen

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Posted 29 April 2021 - 12:57 PM

As Izar can be split in broad daylight, it's not the light pollution... It can thus be either of three things, or all three combined:

 

1) The optical quality of the scope

 

2) The seeing (how turbulent the air is)

 

3) The observer's experience

 

 

If you're unsure of the optical quality of your scope and the seeing, try aiming it at Polaris or another 2nd magnitude star at high magnification. 132x should be okay. The star should be a small, round disk, sharply defined, surrounded by a single, faint, thin ring. If it's a blurry spot, your scope may have poor optics or the seeing is very poor. This will prevent you from seeing tight doubles. 

 

Here's a picture of Izar, taken with my phone through the 6mm ortho (140x) eyepiece of my 63mm Zeiss, a few minutes after sunset, May 19th, 2020. 

 

gallery_55742_4772_472463.jpg

 

 

 

Clear skies!

Thomas, Denmark


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#3 Buqibu

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Posted 29 April 2021 - 01:03 PM

As Izar can be split in broad daylight, it's not the light pollution... It can thus be either of three things, or all three combined:

1) The optical quality of the scope

2) The seeing (how turbulent the air is)

3) The observer's experience


If you're unsure of the optical quality of your scope and the seeing, try aiming it at Polaris or another 2nd magnitude star at high magnification. 132x should be okay. The star should be a small, round disk, sharply defined, surrounded by a single, faint, thin ring. If it's a blurry spot, your scope may have poor optics or the seeing is very poor. This will prevent you from seeing tight doubles.

Here's a picture of Izar, taken with my phone through the 6mm ortho (140x) eyepiece of my 63mm Zeiss, a few minutes after sunset, May 19th, 2020.

Posted Image



Clear skies!
Thomas, Denmark



Thanks, I will try that. Why should there be a faint ring around it?
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#4 cookjaiii

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Posted 29 April 2021 - 01:08 PM

I think that should be an easy split for a 4".  It can be split it with a ST-80 (80mm f/5), but I don't remember at what magnification.  Have you looked at the pattern you get when you slightly defocus a bright star in the center of your field of view at high magnification?  If the optics are decent and properly aligned, it should look like a bull-eye target of concentric rings.  



#5 jrschmidt2

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Posted 29 April 2021 - 01:27 PM

Thanks, I will try that. Why should there be a faint ring around it?

The faint ring at high power will be the Airy disk, which is related to the fact that  there is a limit to how tight you can focus light (due to the diffraction limit).  Exactly how big this diffraction pattern will be depends on the aperture of your scope (which in turn determines the diffraction limit). Basically at high power you will be seeing the diffraction pattern of the single star, rather than a single pin **** (as would be the case in a hypothetical scope of infinite aperture).



#6 aa6ww

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Posted 29 April 2021 - 01:27 PM

I use Izar when its up to tell me how good the seeing conditions are. I also use the double double in Lyra also.

A few weeks ago, my friends Edge 9.25 couldn't split Izar because seeing was barely 3/5. 

For me, its all about the seeing conditions for what I like to observe in my backyard.

 

...Ralph


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#7 Rutilus

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Posted 29 April 2021 - 02:04 PM

With a 4 inch scope, the companion will be visible almost touching the outer edge of the first diffraction ring.

With my 70mm f/17 achromat refractor (drawing made  back in 2010), the companion sits in the middle of the

diffraction ring.

 

Attached Thumbnails

  • Izar-cn.jpg

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#8 StarAlert

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Posted 29 April 2021 - 02:10 PM

I also pick out a close bright double to test the seeing. Right now, I use Algieba. It's close to the zenith. How cleanly it can be split and how much power I can use, gives me a good indication of how steady the sky is.  


Edited by StarAlert, 30 April 2021 - 08:03 AM.

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#9 chrysalis

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Posted 29 April 2021 - 02:28 PM

The Izar (Epsilon Boötis) primary is quite bright at magnitude 2.37, while the secondary is magnitude 5.12. These two pinpoint light sources are separated by only 2.9"  (arcseconds). The magnitude difference and close proximity can make it difficult to see the separate components especially at lower magnifiations.

 

At 132x, 2.9" will appear to your eyes as a separation of a little over 6' (arcminutes), or 1/10th of a degree. This is about 1/5 the width of the full moon; or roughly HALF the separation naked eye of Mizar and Alcor (magnitudes 2 and 4), the middle stars in the handle of the Big Dipper.

 

If you can up the magnification on a good night, you will be able to split this lovely double. Note that at 132x, you are at 33x/inch of aperture, which will only be useful in very steady/transparent/good seeing nights. Traditionally, 50x per inch of aperture has been quoted as highest useful magnification; however, this is often exceeded ESPECIALLY when in relation to double star observing.

 

Best of luck!! Let us know when you succeed!


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#10 Tony Flanders

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Posted 29 April 2021 - 02:40 PM

Izar can be challenging due to the fact that the primary is almost ten times brighter than the secondary, combined with the fact that the stars are fairly close to each other. I generally need well over 100X to split it, and it may be impossible if the seeing is bad enough. But when you do get a clean split, it's truly spectacular due to the contrasting colors.

 

At this time of year Algieba (Gamma Leonis) is very easy to locate, easy to split, and quite lovely. In the summer -- or later at night at this time of year -- it's hard to beat Albireo (Beta Cygni) and the Double Double (Epsilon Lyrae).


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#11 Buqibu

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Posted 29 April 2021 - 02:50 PM

Thanks for all the replies! I will try on the next clear night

#12 CBM1970

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Posted 29 April 2021 - 06:57 PM

I've tried to split Izar a couple of times. I "kinda" got it on my second attempt.  I saw the companion star below the primary (correct for a reflector view, I believe). It was distinctly greenish, but there was no dark lane between the two. Seeing was pretty mediocre, and I was close to 200x.

 

Keep trying and good luck! (I think I'm saying this for the both of us.)



#13 Rutilus

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Posted 30 April 2021 - 07:39 AM

Looking through some old files this morning, I found this drawing made 12 years ago.

4 inch telescope at 270x magnification. My notes tell me that I was able to make out the

companion at 81x.

Attached Thumbnails

  • Izar-102-cn.jpg

Edited by Rutilus, 30 April 2021 - 07:39 AM.

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#14 dhkaiser

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Posted 30 April 2021 - 09:50 AM

Might be best to ask in the double star forum.  

 

I'm relatively new to DS observing and did split Izar with my 4" f/7 scope.  Took a high power as I recall, something like 255x.


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#15 cuzimthedad

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Posted 30 April 2021 - 10:42 AM

Moving to the Double Star Observing


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#16 Tyson M

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Posted 30 April 2021 - 11:07 AM

Izar can be a challenging split if the conditions are not good. I have split it with I believe an 80mm apo refractor before.

 

For sure a 4" as well.


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#17 rugby

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Posted 30 April 2021 - 03:32 PM

In the past I have mistaken the field of Izar with the field of Rho and Sigma.
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#18 Bonco2

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Posted 30 April 2021 - 03:40 PM

Izar is one of my favorites with my 60mm f15 Unitron @ 130X

Your short 660mm fl 4 inch scope may not be up to the task. While it is capable of useful double star observations it certainly is not the ideal setup for tight doubles. In any case don't give up, try, try, and try again.

Good luck, Bill  


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#19 StarAlert

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Posted 30 April 2021 - 04:37 PM

Buqibu,

You didn’t mention what time you tried this. At 9pm it’s only at 38o alt. If you can take a look after 11pm, it’ll be above 60o. At 1am it’s near zenith. The higher, the better.  


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#20 sunrag

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Posted 02 May 2021 - 11:13 AM

I live in Bortle 6, and i have no problem splitting Izar using a home made 4” /F9 achro. The separation is well within resolving power of aperture greater than 80mm. However, due to unequal brightness of the two stars, the fainter one is hard to see.

Try the Double-Double in Lyra constellation (epsilon Lyrae). The angular separation is about the same as Izar binary, but the with the magnitudes being about equal, they are easier to see.
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#21 John Fitzgerald

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Posted 03 May 2021 - 09:50 PM

Epsilon Bootis (Izar): The split is very seeing dependent, no matter the size of telescope.  In very poor seeing, no telescope can separate the pair.


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#22 Bigal1817

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Posted 05 May 2021 - 02:28 PM

I posted this in another forum but it appears to fit here as well, so I will repost.  I own an 8" GSO Dobsonian as my workhorse to split stars. After a recent rainstorm passed, the seeing was above average and I split Izar at 150x. With my 4" achromat at the same 150x, I could not split Izar. Both of these telescopes are not fancy but they're a start and I enjoy using them.

2 scopes

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#23 Bonco2

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Posted 05 May 2021 - 03:51 PM

Short focal length refractors must have very good optics to be sharp at high magnifications. However they are great for wide field views.  Small achro refractors from 60mm to 100mm at f/12 and above are more forgiving. I find the sweet spot for double stars with achro's is 60mm at f/15, 75mm at f/16, 100mm at f/12 to 15.  A 100mm longer than f/12 requires a substantial mount. My personal favorite is 75mm at f/16.

For small reflectors in the 150mm to 200mm range I prefer f/6 thru f/8 for high power double star use. Longer would be better except for the inconvenience.  This is not to say that shorter f ratios for either refractors or reflectors aren't capable for rewarding double star use it's just they are not ideal for high power observations of difficult doubles.

Bill  


Edited by Bonco2, 05 May 2021 - 03:53 PM.

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#24 StarAlert

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Posted 05 May 2021 - 04:06 PM

I pointed my new (to me) MK91 (228mm, f/13.5) at Izar a couple nights ago. The beautiful blue secondary was screaming in my face. 


Edited by StarAlert, 06 May 2021 - 08:50 AM.

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#25 flt158

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Posted 06 May 2021 - 08:29 AM

I pointed my new MK91 (228mm, f/13.5) at Izar a couple nights ago. The beautiful blue secondary was screaming in my face. 

Do you know what magnification you used, Star Alert?

 

Clear skies from Aubrey. 




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