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Alpha UMa ( Dubhe) observation satellite +1.79 + 4.95, sep 0.7 "using a telescope of 170 mm

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#1 Konstantin 1980

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Posted 17 April 2016 - 02:11 PM

Alpha UMa observation satellite using a telescope of 170 mm. Brightness  Components AB: .. 1,79 + 4,95, 0,7" division "Zoom 300 x (+ Binoviewer deepsky)  . Satellite saw excellent weather conditions - seeing 9. Many times I tried to see it in the winter, but the atmosphere did not allow two days ago I made it easy, I did not suspect that the satellite can be seen in 170 ns telescope (254 mm reduced to 170 mm)  

two stars are seen separately, but the satellite is sometimes merges with the ring being dissolved in it. However, sometimes it is seen as a clear bead on the ring.

 

ps ( a telescope with a diameter of 254 mm , 400х +  Binoviewer deepsky -  Both stars are seen just fine, clearly and separately) 


Edited by Konstantin 1980, 17 April 2016 - 02:29 PM.


#2 fred1871

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Posted 17 April 2016 - 09:48 PM

Odd, really, that the companion in the presumably best seeing moments is "a clear bead on the ring",  as the Rayleigh Criterion for 170mm is 0.8", and the ephemeris (6th Orbit Catalogue) for this 44.5-year binary gives ~0.75" at present, so the companion should near-enough be in the gap between disc and first diffraction ring. With 3+ magnitudes difference it will be a much more difficult object than an equal pair at that separation.

 

Did you stop down the 254mm telescope because the first diffraction ring would be centred at about 0.72" - which would have placed the companion more directly on the diffraction ring?


Edited by fred1871, 17 April 2016 - 10:16 PM.


#3 Konstantin 1980

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Posted 17 April 2016 - 11:50 PM

Odd, really, that the companion in the presumably best seeing moments is "a clear bead on the ring",  as the Rayleigh Criterion for 170mm is 0.8", and the ephemeris (6th Orbit Catalogue) for this 44.5-year binary gives ~0.75" at present, so the companion should near-enough be in the gap between disc and first diffraction ring. With 3+ magnitudes difference it will be a much more difficult object than an equal pair at that separation.

 

Did you stop down the 254mm telescope because the first diffraction ring would be centred at about 0.72" - which would have placed the companion more directly on the diffraction ring?

I reduced to 170 just to learn how to be seen. In 254, it was obvious just fine. So I decided to reduce this figure to see or not. It turned out that it is possible to see well enough. Perhaps it would be seen in the 150, but I have not tested. and I think it will be seen, the detection limit in my opinion, about 130 mm

the atmosphere was not very quiet, but the satellite signs were clearly visible, today I will try to be reduced to 130 mm on to see how it will be seen

254 mm was clearly visible separately as a circular disk. With a great atmosphere, it was seen  clearly and confidently, I even forgot about the complexity of this star.


Edited by Konstantin 1980, 18 April 2016 - 12:07 AM.

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#4 Cotts

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Posted 18 April 2016 - 10:00 AM

Konstantin, I will try this with my 12.5" (317.5mm) Lockwood/Teeter Dob at the Texas Star Party....  If you found it 'obvious' in  your 254mm I should be able to have success if the seeing cooperates...

 

Fred, what is the arithmetic for the first two or three rings in terms of aperture in mm?  I know the Dawes (0.365") and  Rayleigh (0.436") numbers for my scope...

My secondary obstruction is 17.6% which does affect the location of the rings a bit if I recall correctly.......

 

thanks,

 

Dave



#5 Konstantin 1980

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Posted 18 April 2016 - 10:10 AM

Konstantin, I will try this with my 12.5" (317.5mm) Lockwood/Teeter Dob at the Texas Star Party....  If you found it 'obvious' in  your 254mm I should be able to have success if the seeing cooperates...

 

Fred, what is the arithmetic for the first two or three rings in terms of aperture in mm?  I know the Dawes (0.365") and  Rayleigh (0.436") numbers for my scope...

My secondary obstruction is 17.6% which does affect the location of the rings a bit if I recall correctly.......

 

thanks,

 

Dave

254 mm Newton and relaxed atmosphere satellite was seen perfectly. However, increasing the diameter of the telescope entails and atmospherics, since the increase, too, must change. I advise you to reduce your 317.5 to my 254 mm , if you can not see with a telescope 317.5mm 

success will be in good atmosphere, definitely.


Edited by Konstantin 1980, 18 April 2016 - 10:13 AM.


#6 Organic Astrochemist

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Posted 24 April 2016 - 03:06 PM

I have never been able to split difficult Dubhe.

I failed again last night, seeing 4/5, 200X, 250X, 300X, 500X and 1000X.

Even at highest magnification, elongation in Zeta Bootis was obvious and the color contrast in Izar was striking.

For Dubhe, the first and second diffraction rings often fused together to form a single band, but no evidence of elongation or multiplicity. At the ridiculous power of 1000X the airy disk was big and round.

 

The OP didn't mention the color of the pair. Based on Izar, I would be curious.



#7 Redbetter

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Posted 24 April 2016 - 08:02 PM

Haven't had the seeing for such a close, 3+ delta magnitude pair in the 20" or 10".  Getting hints and can see color contrast, but without a semi-stable inner diffraction pattern and airy disks there is not much more I can do with this type of pair.

 

If you run Konstantin's case through Aberrator for 254 mm aperture, 25% obstruction and assuming the 0.75" separation the second component is showing up roughly centered on the first diffraction ring.  It moves in somewhat, but is still on the ring with 170mm aperture (working out to about 37% obstructed.)  While I'm not sure I trust Aberrator's representations of wider delta M pairs, this one is within a range that it should be able to display, although I would expect the diffraction rings to typically be fuller than what the program shows.  The shape of the second component is odd looking as a result of the calculated intensity patterns.  I doubt our eyes would interpret it the same way.



#8 Redbetter

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Posted 24 April 2016 - 08:24 PM

 

Fred, what is the arithmetic for the first two or three rings in terms of aperture in mm?  I know the Dawes (0.365") and  Rayleigh (0.436") numbers for my scope...

My secondary obstruction is 17.6% which does affect the location of the rings a bit if I recall correctly.......

 

 

 

From the optics-net site it looks like the maxima are nearly unchanged for the disk, 1st, 2nd, and 3rd rings when going from 10 to 20% obstruction.  The minima however do shift several percent.  Interpolating for your scope and assuming 550 nm wavelength I get:

Minimum of the Airy disk:  0.42"

Maximum of 1st ring:  0.58"
Minimum after 1st ring: 0.83"
Maximum of 2nd ring: 0.96"
Minimum after 2nd ring: 1.12"
Maximum of 3rd ring: 1.32"
Minimum after 3rd ring: 1.55"

 

Interpolating may not be the best way to do it, and the assumed wavelength could be adjusted, but these should be close if the table I pulled the original values from was accurate.



#9 fred1871

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Posted 24 April 2016 - 10:17 PM

I'd overlooked getting back to this discussion. :(

Redbetter's numbers above look much the same as I'd calculate for a 12.5-inch scope and a small obstruction ratio.

 

A point to notice is that the second diffraction ring is often so dim as not to be easily seen, and the 3rd ring likewise. However their intensity relative to each other changes with CO ratio.

 

Using Chris Lord's table, from his Brayebrook Observatory site, we can see that compared to an unobstructed aperture, where the rings are fainter as one goes outwards, with 0.2 CO the third ring becomes brighter and the second less bright; that remains true for 0.33 CO; but at 0.4 CO the second ring is brighter again and the 3rd very dim. With each increase in CO the first ring becomes brighter. The shift of light from the disc to the rings has to show up somewhere :)

 

A curious factor is that some telescopes seem to throw up brighter rings than might be expected for the 2nd and 3rd ring. It doesn't always match up to other scopes of the same aperture and similar CO, which might suggest internal reflections enhancing the rings. There can also be effects from spherical aberration, whether from optical imperfection or induced by falling temperatures.

 

And seeing variability can of course make the location of a secondary star relative to a ring somewhat changeable in appearance, especially with flickery seeing. 



#10 Redbetter

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Posted 25 April 2016 - 12:08 AM

I didn't post the following before because they are interpolations that are subject to even greater compounding of errors, but here are the intensities of the maxima of the rings for Dave's scope, normalized to 1 for the airy disk center:

Airy disk:  1  

1st ring:  0.0263
2nd ring: 0.0022
3rd ring: 0.0032
 

Keep in mind that unlike the relatively small shifts in ring locations, the intensities change a great deal between 10 and 20% obstructed, so these values are more approximate.  Still they give an idea of the relative magnitudes of the intensity peaks.  In this case the ratios for Airy disk/1st/2nd/3rd ring peaks are:  455 : 12 : 1 : 1.5    This illustrates what Fred was saying about the later diffraction rings. 

 

Notice that for this scope the peak intensity of the 1st ring is almost exactly 4 magnitudes less than the peak of the airy disk.  So as the delta M starts to approach 4 it will be getting far more difficult to distinguish the companion in this zone--peaking at 0.58" but probably extending out some fraction of the distance to the next minimum at 0.83".  Seeing, thermals, collimation, focus adjustment, and the quality of the optics all need to be good.  Or at least that is how I interpret it. 



#11 cildastun

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Posted 27 April 2016 - 03:19 AM

Interesting discussion. From theory, I would not have expected to see this one at all with my SW 180 Mak, but I gave it a try last night when the clouds parted enough. Seeing was about 4/5 near the zenith, much poorer further down.

 

There was a clear bright spot seen on the inside of the diffraction ring at x340 (which was also visible at x225 but more difficult to estimate the position). There were no other bright spots around the ring or any other visible artefacts. I estimated PA to be about 350 degrees from drift direction, which seems about right. (I also swung across to Zeta Bootis afterwards, which was elongated to a clear peanut).

 

Chris



#12 Organic Astrochemist

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Posted 28 April 2016 - 11:25 AM

I had excellent seeing last night -- I could see at least 3 diffraction rings perfectly. (I could also see off-axis coma and out-of-focus aberrations)

Given my central obstruction, my first diffraction ring is both bright and broad (I believe it has a max near 0.94"), which is very unfortunate when try to observe a separation at 0.8" and a large delta mag.

At 500X I though I saw glimpses of a brightening of the ring in approximately the right location.

At 1000X everything is dimmer including that first diffraction ring. Towards the center of the field of view, the image of the companion superimposed on top of the ring became clearer. It was never a great image, but as Chris said, there were no other bright spots around the ring.

This is probably an example (of many) where an optical design other than a newtonian might be better to resolve the pair.



#13 cildastun

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Posted 02 May 2016 - 06:08 AM

]It would be interesting to know what the calculated figures for a SW 180 Mak Pro would be for first ring , dark space etc.

 

In practice, this is what I get on a well-defined pair (Algieba) on a night of average seeing:-

 

[attachment=691126:compositealgieba.jpg

 

4 still images stacked in PS, using  an ASI224 MC camera

 

Apparent Airy disk diameters, 0.77 and 0.85 arcsec

1st Ring (Algieba B), 0.9 arcsec

Dark space, 0.3 to 0.7 arcsec

 

This implies that secondaries would be seen much closer than the normal formula. Can't be right?

 

Chris



#14 cildastun

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Posted 02 May 2016 - 06:12 AM

It would be interesting to know what the calculated figures for a SW 180 Mak Pro would be for first ring , dark space etc.

 

In practice, this is what I get on a well-defined pair (Algieba) on a night of average seeing:-

 

4 still images stacked in PS, using  an ASI224 MC camera

Apparent Airy disk diameters, 0.77 and 0.85 arcsec
1st Ring (Algieba B), 0.9 arcsec
Dark space, 0.3 to 0.7 arcsec

 

This implies that secondaries would be seen much closer than the normal formula and would explain the secondary of Alpha UMa being seen as a spot just inside the first ring. Can this be right?

 

Chris

 

compositealgieba.jpg


Edited by cildastun, 02 May 2016 - 06:20 PM.


#15 Redbetter

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Posted 04 May 2016 - 02:19 AM

Chris, 

 

I roughed out a table for your scope assuming a 41 mm obstruction (got that from a website somewhere) yielding 22.8% CO.  The first ring maximum radius is at 1.02" per my table.  That is 2.04" diameter.  When I measure the smaller star from roughly the center of brightness of the ring on either side and in the same PA as the pair, I come up with a scale that I can then apply to the total separation.  In this case 2.04" = 10 mm on my screen.  I measured the center difference of the pair as 22.5 mm on the same axis.  This works out to a separation = 22.5 * 2.04/10 = 4.59".  WDS gave the last reading in 2014 as 4.6" and Sue French in her recent article had it at 4.7" per the orbit.  (The calculated value I got above is in closer agreement than I would have expected.  Checking again I think I see the ring as being closer to 9.5mm across at the centers...which would give 4.83".)

 

My take on the difficulty of using the airy disk itself as a measure of scale is that it is more variable in apparent diameter because it has to be measured at the minimum.  Where this minimum is placed can depend on how bright the star itself is, seeing, magnification, etc.  Aiming for the brightest/central portion on either side of the first ring has two advantages in determining scale:  it is less impacted by brightness of the airy disk, it is also wider yielding greater precision for the same measurement area.   That second effect improves the precision by ~30% even if the magnitude of the error in determining the diameter is the same for both the ring and disk. 

 

I calculate your airy disk radius (interpolated minimum from the table) at 0.72".  So if I am right the processed values you got are reading a little high, but that probably isn't a surprise considering the relative brightness of the Algieba pair.



#16 cildastun

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Posted 04 May 2016 - 04:47 AM

Chris, 

 

I roughed out a table for your scope assuming a 41 mm obstruction (got that from a website somewhere) yielding 22.8% CO.  The first ring maximum radius is at 1.02" per my table.  That is 2.04" diameter.  When I measure the smaller star from roughly the center of brightness of the ring on either side and in the same PA as the pair, I come up with a scale that I can then apply to the total separation.  In this case 2.04" = 10 mm on my screen.  I measured the center difference of the pair as 22.5 mm on the same axis.  This works out to a separation = 22.5 * 2.04/10 = 4.59".  WDS gave the last reading in 2014 as 4.6" and Sue French in her recent article had it at 4.7" per the orbit.  (The calculated value I got above is in closer agreement than I would have expected.  Checking again I think I see the ring as being closer to 9.5mm across at the centers...which would give 4.83".)

 

My take on the difficulty of using the airy disk itself as a measure of scale is that it is more variable in apparent diameter because it has to be measured at the minimum.  Where this minimum is placed can depend on how bright the star itself is, seeing, magnification, etc.  Aiming for the brightest/central portion on either side of the first ring has two advantages in determining scale:  it is less impacted by brightness of the airy disk, it is also wider yielding greater precision for the same measurement area.   That second effect improves the precision by ~30% even if the magnitude of the error in determining the diameter is the same for both the ring and disk. 

 

I calculate your airy disk radius (interpolated minimum from the table) at 0.72".  So if I am right the processed values you got are reading a little high, but that probably isn't a surprise considering the relative brightness of the Algieba pair.

Thanks for this; I took it the other way round, ie assumed that the 4.6 arcsec separation was fixed and used that as the scale to estimate ring radius etc.

 

My worry was that the dark space radius would imply that I could see secondary stars at a much closer separation than theory would allow, ie 0.3 to 0.7 arcsec,rather than the theoretical 0.7 arcsec.

 

Chris



#17 Redbetter

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Posted 05 May 2016 - 03:21 AM

 

Thanks for this; I took it the other way round, ie assumed that the 4.6 arcsec separation was fixed and used that as the scale to estimate ring radius etc.

of the Algieba pair.

 

My worry was that the dark space radius would imply that I could see secondary stars at a much closer separation than theory would allow, ie 0.3 to 0.7 arcsec,rather than the theoretical 0.7 arcsec.

 

Chris

 

 

For near equal doubles I would expect to be able to see apparent separation slightly below the Rayleigh criteria, particularly if the components are not overly bright.  I've gotten some impression of this in 70 and 80 mm apertures with cheap fast doublet refractors.  But what would be more interesting is if the same can be detected with dimmer components in larger apertures.  I've not had the seeing lately to really test this on tight pairs of 7th or 8th magnitude.  This would rely on being able to apply enough magnification that the area in between the disk centers would tend more toward the threshold of visibility when staring at the two less intense disks.  I've read some that this really doesn't happen, because the eye tends to adapt to the dimmer targets keeping the airy disk closer to nominal size as long as the pairs are not mismatched, but it still interests me.  At the extremes (even dimmer) I would expect it to be more apparent. 

 

Here is what I worked up for your scope based on 22.8% central obstruction (and it might be a little higher than that depending on what the 41mm number was referring to.)

Radius (arc sec)
Airy disk min. 0.72"
1st ring max. 1.02"
1st ring min. 1.50"
2nd ring max. 1.71"
2nd ring min. 1.95"
3rd ring max. 2.31"
3rd ring min. 2.71"



#18 Redbetter

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Posted 18 May 2016 - 12:53 AM

I tried a different approach tonight with the 20" but didn't start early enough before the seeing changed.  I put an 80A blue filter on at 500x to mute some of the prominent wavelengths of the primary, make the light less chromatic, and perhaps beat the seeing.  I hoped this wavelength would slightly boost the secondary vs. the primary.   Initial inspection of the images looked like it would work, so I slipped on my new home made PA scale and set it via a few drifts.  Then the seeing started falling apart.  Oh well.   I got some hints of a companion again at a PA of roughly 330.  I did not remember what the orbit looked like when I tried this so I was suitably blind to PA.

 

It was still too bright for the dancing seeing, so I switched to a 25 red filter which I knew would knock the total light output down tremendously, but cost about 15% or more of the theoretical resolution.  This was still too bright for the seeing so I put on the 8" off axis mask along with the filter.  This helped a lot by dimming things and making a larger, somewhat more stable airy disk, but it did not make the inner ring stable.  The disk was not appearing fully round.  Instead it was noticeably egg shaped in a PA of about 345.  (This was measured after adjusting for drift again since the field continued to rotate.)  I neglected to do a comparison on a bright non-binary star, so I can't rule out some other effect related to the section of the aperture used.  At any rate this is a very low confidence result because the disk was moving too much to examine meaningfully, even though its egg shaped nature was visible.  It makes for an odd case when run through Aberrator using only the red light element, not as egg shaped but an uneven peanut with one end on the first diffraction ring.

 

The PA measurement is very rough and based on a wheel I made with 15 degree gradations.  I did blind PA's on three doubles the night before with none worse than 15 degrees off the projected orbit when I checked later, so it works despite being crude.

 

When I get some good seeing again I am going to swing the scope this way.  I had some the other night, but forgot about Dubhe until too late.  Filters might be the answer, perhaps even some sort of neutral density filter in combination with a color filter?


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#19 drollere

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Posted 06 June 2016 - 12:06 PM

Interesting discussion. From theory, I would not have expected to see this one at all with my SW 180 Mak, but I gave it a try last night when the clouds parted enough. Seeing was about 4/5 near the zenith, much poorer further down.

 

There was a clear bright spot seen on the inside of the diffraction ring at x340 (which was also visible at x225 but more difficult to estimate the position). There were no other bright spots around the ring or any other visible artefacts. I estimated PA to be about 350 degrees from drift direction, which seems about right. (I also swung across to Zeta Bootis afterwards, which was elongated to a clear peanut).

 

once again, what you see is not reliably predicted from theory and catalog data, especially the four significant digits type of calculation ... a point i've made many times in this forum.

 

sidgwick's caution about "theory" is frequently forgotten:

 

"At normally encountered ƒ/ratios (say, ƒ/5 to ƒ/20) no intensity gradient across the disc is perceptible, the border between the disc and the first minimum appears nearly sharp, and the rings are brighter than theory would indicate, the first ring being not much fainter than the disc itself. ... The visible extent of the disc, like the number of rings visible, varies for a given instrument with the brightness of the source, although the discs are in fact the same size, irrespective of brightness."

 

or vasco ronchi:

 

Vasco Ronchi (1961) noted the important difference between the ethereal image or unseen physical characteristics of the actual star, the calculated image or theoretical representation of this image in an optical instrument, and the detected image that actually appears to the astronomer's eye. Remarkably, optical theory in the form of the calculated image, a "mere mathematical construction," does not describe the detailed visual appearance of a stellar detected image.

 

i think it was konstantin who reported rodlike appearance in matched binaries below the resolution threshold, which some people ruled "impossible" or "unbelievable" based on optical calculations. yet van den bos made the very acute judgment, based on unimpeachable experience, that visual perception is not simply an optical task:

 

The born double star observer is probably, like the artist, the type with the highly developed nervous system, with the lightning-like reaction; to speak in present day terms [this is in 1944]: the born fighter pilot. It is not enough that the eye forms a faithful image of very fine structure on the retina; the optical nerve and the brain must be able to follow instantly the perceptual changes of the star image and to interpret them correctly. It seems that to a person of slower nervous reaction, no matter how keen his eye may be, the telescopic image of a difficult double star becomes just a patch of light, in no way differing from that of a single star. Even among the born double star observers there appear to be significant differences however. For instance, having dealt with a great mass of observational material, I am left with the impression that, while Burnham was on the one hand not quite so good as Aitken or Hussey in discovering pairs far below the separating power of the instrument, but with components of nearly the same brightness, he was unrivaled when it came to making out a faint companion close to a bright primary — undoubtedly the most difficult type of double star to deal with.

 

note that he clearly equates a significant part of the observational task as dependent on "brain stuff" beyond the retina, and the fact that "the separating power" doesn't limit detection or discovery.

 

optical performance is optical, and visual perceptions are visual. you can't equate one with the other. i'm continually surprised that people cheerfully take optics as the rule of law for perception, then get out their pocket calculators and dictate visual appearance to the milliarcsecond of separation and the ten thousandth part of brightness.

 

some posts above describe clever methods to troubleshoot and overcome observing difficulties. a great part of double star observing at the limit involves persistence, patience, good conditions, and trial and error methods to eliminate obstacles or find the "just so" magnification necessary for the challenge.


Edited by drollere, 06 June 2016 - 12:14 PM.

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