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What minimum degree of binary star separation can I expect from a quality mid size APO

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#26 Jon Isaacs

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Posted 16 October 2020 - 09:50 AM

I have had big Newts.  I have a 12 inch now.  Their performance is lacking on the close, unequal doubles I like most to view and challenge myself with.  It's probably a combination of central obstruction, fast focal ratio, and spider vanes.  A slow, unobstructed reflector design might work, but it would be as long, and might be nearly as costly as the equivalent apo, if the optics are custom made by an expert mirror maker.

A big Newt has worked ok for me on the unequal ones that have wider spacing, like Xi Peg, or the very tight equal doubles.  They fail on double stars like 90 Herculis, at least in my experience.

 

I haven't tried 90 Herculis but it looks very doable to me. When I'm back in San Diego along the coast where the seeing can be very good, I'll give it a try.  

 

I think the biggest issue with a Newtonian is thermal. To split the tough unequal doubles, besides the good seeing, it takes real time to reach rock solid thermal stability even with aggressive ventilation. 

 

Jon


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#27 jjack's

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Posted 17 October 2020 - 03:04 AM

You can find orbital changes and graphs on this website, very usefull : http://dibonsmith.com/orbits.htm

A gold mine of information there, but in french language : orbital graphs from  dibon smith : http://www.astrosurf...ard/observ.html



#28 jjack's

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Posted 17 October 2020 - 03:20 AM

Eta corona borealis is a very interesting binary moving quickly in its orbit.

i could split them the last 2015 with my C8 (touching) but now they are too close together. 

We must wait to 2025 to see them again (around 0.6").

I like to see binary stars in my 4" refractor too because airy patterns are very beautifull to look at.


Edited by jjack's, 17 October 2020 - 03:23 AM.


#29 ASTERON

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Posted 17 October 2020 - 04:33 AM

$10 bucks shipped hundreds of double stars accessible in a 4 inch telescope.  And many many deep sky objects also accessible in small apertures.  And all of them, or almost all, very attractive in larger scopes.

 

https://www.willbell...TLAS/atlas1.htm

 

 Mind you,  Just $10  + $64.95 shipping, will get me the same shipped to Israel.bawling.gif

 

For ages I have been begging Willman Bell  to ship me books by regular airmail ( I was willing to take a chance with the books not reaching me.....  They still insist on using the most expensive shipping method in existence !

I think their stubbornness they lost my business worth literally $Ks  by refusing to ship by regular air-mail bangbang.gif  


Edited by ASTERON, 17 October 2020 - 05:43 AM.

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#30 fred1871

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Posted 17 October 2020 - 05:31 AM

There's always a "different" measure can be found for many double stars. 52 Orionis, referred to by Jon Isaacs recently (including typo mis-naming), is a very long period binary where the separation is presently decreasing, and will continue decreasing for many years to come if the orbit diagram (as Stelle Doppie shows it) is anywhere near correct. The measures list for recent decades show it is.

 

The Ephemeris suggests 1.0" rather than 1.1" at present; the measures agree with this. Examples, speckle by the Scardia group in 2009 had 1.03"; most recent I've seen in WDS is 0.968" in 2019, the source I haven't traced yet, but 3 decimal places is normally a speckle result.  Closing is not quick, that's measures 10 years apart. So this year the separation is pretty certainly a whisker under 1.0".


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#31 rigelsys

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Posted 17 October 2020 - 12:18 PM

If you'd like to test yourself,  here's a project you can try

 

http://rigelsys.com/...Resolution.html



#32 rigelsys

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Posted 17 October 2020 - 12:21 PM

And if any other newbies are interested, here's some more projects :-)

 

http://rigelsys.com/projects.html


Edited by rigelsys, 17 October 2020 - 12:21 PM.


#33 daquad

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Posted 17 October 2020 - 02:48 PM

There's always a "different" measure can be found for many double stars. 52 Orionis, referred to by Jon Isaacs recently (including typo mis-naming), is a very long period binary where the separation is presently decreasing, and will continue decreasing for many years to come if the orbit diagram (as Stelle Doppie shows it) is anywhere near correct. The measures list for recent decades show it is.

 

The Ephemeris suggests 1.0" rather than 1.1" at present; the measures agree with this. Examples, speckle by the Scardia group in 2009 had 1.03"; most recent I've seen in WDS is 0.968" in 2019, the source I haven't traced yet, but 3 decimal places is normally a speckle result.  Closing is not quick, that's measures 10 years apart. So this year the separation is pretty certainly a whisker under 1.0".

That's good to know, since I was able to split it a few nights (mornings) ago with my 4" f/15.5 45-year-old Jaegers refractor.  Of course, the two visible discs were slightly merged, but the dual nature was obvious at 225X.

 

Thanks for that info.

 

Dom Q.



#34 John Huntley

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Posted 17 October 2020 - 07:15 PM

I think David Knisely's definitions are helpful:

 

post-3169-14074143332622_thumb.jpg


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#35 Stozhary

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Posted 17 October 2020 - 11:16 PM

Do you observing visual or use camera. Both have "+" and "-". Digitally you can reduce exposure time and this way you have more choices of objects. I think seeing condition is main limit. Try to see zeta Aquarius 4.5-4.6 mag with 3 arcsec separation. Star atlas or planetarium software could give you idea what to look.

Clear skies!

Stozhary

Just return from my back yard. Tested my 132FLT F/7 scope. 925 mm focal distance 4.7 mm Explore Scientific eye piece. Magnification 925/4/7=197x. I tried to add Televue 2x barlow but stars look too dark for my eye. So, targets:

Mesartim γ Aries 4.8-4.8 magnitude double 8"separation. Very easy to see big separation in eye piece;

Then 65 Pisces 4"separation equal magnitude stars, Also distinctive separation between stars. It looks like possible to resolved 2-3" binary star but I wasn't able to find appropriate target tonight. So, I think it's very likely to split through 132 mm aperture scope 2 arcsec binary system.

Thanks

Stozhary



#36 fred1871

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Posted 18 October 2020 - 01:43 AM

The Dawes Limit (practical observing) and the Rayleigh Criterion (diffraction) are useful starting points. The Dawes Limit is based on work by WR Dawes in the 19th century experimenting on near equally bright pairs of stars around 6th magnitude, establishing 4.56"/A where A is the aperture in inches - in Metric, it's 11.58"/A in cm. He used a variety of apertures of modest size in establishing this, using refractors up to a bit over 8 inches diameter. The appearance of the pair at the DL approximates to discs in contact: depending on the night and optical quality, this can appear yo the observer as somewhere from  a hairline separation to a slight overlap.

 

Rayleigh Criterion is 5.43"/A in inches, or Metric 13.8"/A in cm. Appearance will usually be marginal separation. With unequally bright stars, different by perhaps 2 or 3 magnitudes, this is the likely limit for resolved or split pairs.

 

There will be some small variation caused by a central obstruction (CO), how much difference depends on its diameter relative to the aperture. It changes the diffraction pattern (reflectors in general) compared to refractors (the commonest unobstructed form). CO puts more light into the diffraction rings of the star image, compared to unobstructed; how much depends on relative size. Unequal pairs are generally easier in refractors than reflectors, equal telescope size assumed.

 

Seeing conditions (air steadiness) are the usual limiting factor as apertures get larger. Optical quality and telescope tube thermals have their effects. Observer eyesight and experience matter as well.

 

Overall, the issues for the double star observer are pretty similar to those that affect the planetary observer. Sharpness (resolution) is more critical than light gathering.

 

That's a brief starting summary. grin.gif  You can work out the numbers for any particular telescope size.


Edited by fred1871, 18 October 2020 - 01:53 AM.

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#37 Cpk133

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Posted 18 October 2020 - 11:00 AM

I haven't tried 90 Herculis but it looks very doable to me. When I'm back in San Diego along the coast where the seeing can be very good, I'll give it a try.  

 

I think the biggest issue with a Newtonian is thermal. To split the tough unequal doubles, besides the good seeing, it takes real time to reach rock solid thermal stability even with aggressive ventilation. 

 

Jon

 

90 herc is child's play at 1.6" mag 8.8, 5.2  



#38 John Fitzgerald

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Posted 18 October 2020 - 11:09 AM

90 herc is child's play at 1.6" mag 8.8, 5.2  

Not in my seeing.


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#39 daquad

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Posted 19 October 2020 - 06:53 PM

90 herc is child's play at 1.6" mag 8.8, 5.2  

I haven't tried that one, but I think I should be able to split it with my 4" Jaegers refractor.  This past Sunday morning in 5-6/10 seeing I split:

 

Zeta Orionis (1.9/3.7, 2.6").  Image was unsteady and I could not see the companion at 126X.  At 175X the companion was seen as a bulge on the diffraction ring of the primary.  At 225X the companion showed a nice disc interrupting the diffraction ring of the Primary.  Reminded me of Delta Cygni.

 

32 Orionis (4.4/5.8, 1.2") .  At 225X the image was unsteady, but the companion was clearly separated from the primary.  My notes have the discs just touching.  (The separation was for 2004;  must have opened up since then.)

 

33 Orionis (5.7/6.7, 1.9").  Clean split with black sky between the components at 175X and 225X,  The companion was easily seen at 126X. 

 

Dom Q.


Edited by daquad, 19 October 2020 - 06:57 PM.


#40 Jon Isaacs

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Posted 19 October 2020 - 07:30 PM

32 Orionis (4.4/5.8, 1.2") .  At 225X the image was unsteady, but the companion was clearly separated from the primary.  My notes have the discs just touching.  (The separation was for 2004;  must have opened up since then.)

 

Stelle Doppie lists the separation at 1.40", Sky Safari at 1.4".

 

Its also only 1.3 magnitudes difference. 

 

https://www.stelledo...icerca= Search

 

Goodtostargaze is saying the seeing should be 0.6" but it's looking like the clouds will get me.

 

 

Jon



#41 John Fitzgerald

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Posted 19 October 2020 - 07:33 PM

Most nights I cannot even split Delta Cygni, in any aperture up to 12 inches.  Seeing rules.


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#42 Nippon

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Posted 19 October 2020 - 08:54 PM

Rather than splitting doubles right at the limit of the instrument in use I find the color contrasts of many doubles to be the fun part. Unequal relatively close pairs with contrasting colors are my favorite.


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#43 dhkaiser

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Posted 19 October 2020 - 09:41 PM

Rather than splitting doubles right at the limit of the instrument in use I find the color contrasts of many doubles to be the fun part. Unequal relatively close pairs with contrasting colors are my favorite.

Examples?



#44 Jon Isaacs

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Posted 20 October 2020 - 06:14 AM

Rather than splitting doubles right at the limit of the instrument in use I find the color contrasts of many doubles to be the fun part. Unequal relatively close pairs with contrasting colors are my favorite.

 

For me, it's not this or that, it's this and that.  There are so many doubles of all types and descriptions, that's what makes them so exciting.  

 

Last night was supposed to have excellent seeing but be cloudy.  Instead, it was clear with so-so seeing.  Delta Cygni was an easy split but the primary was not sharp.  

 

90 Herculis and Zeta Herculis were not split.

 

Jon


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#45 daquad

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Posted 20 October 2020 - 09:11 AM

Stelle Doppie lists the separation at 1.40", Sky Safari at 1.4".

 

Its also only 1.3 magnitudes difference. 

 

https://www.stelledo...icerca= Search

 

Goodtostargaze is saying the seeing should be 0.6" but it's looking like the clouds will get me.

 

 

Jon

Yeah, I thought the 1.2" from 2004 was too close.  Thanks for the update.

 

Dom Q.


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#46 Nippon

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Posted 20 October 2020 - 09:20 AM

Examples?

Sigma Cassiopeiae is a really nice one and of course Albireo. Oh and Izar in Bootis 


Edited by Nippon, 20 October 2020 - 09:25 AM.

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#47 dhkaiser

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Posted 20 October 2020 - 10:18 AM

Sigma Cassiopeiae is a really nice one and of course Albireo. Oh and Izar in Bootis 

Thanks, I have done Izar and Albireo, next opportunity I will look at Sig Cas.



#48 daquad

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Posted 20 October 2020 - 12:55 PM

Thanks, I have done Izar and Albireo, next opportunity I will look at Sig Cas.

Beta Monocerotis is a very nice triple.  This has morphed to the doubles forum. blush.gif

 

Dom Q.




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